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#3 Ease of Use of Spray Containers for Users with ArthritisA study of ease of use issues and potential design solutions for designers and consumers.

W. Bradley Fain, Ph.D.Liz Weldon, M.S.Carl Blunt, M.S.

February 2011

PrefaceThis monograph documents the methods and results of research conducted in the Accessibility Evaluation Facility (AEF) of the Georgia Tech Research Institute. The AEF has performed a series of ease of use evaluations for the Arthritis Foundation, the Arthritis Society of Canada, and industry customers. Although information about the outcome of specific evaluations has been withheld, the data and recommendations presented in this monograph are based upon general outcomes and lessons learned from research and product evaluations conducted at the Georgia Tech Research Institute.

For additional information about this monograph, please contact:

Dr. Brad FainGeorgia Tech Research Institute

ELSYS / HSID / HSEB Mail Code 0837Atlanta, GA 30332-0837

Voice: (404) 407-7261Fax: (404) 407-9261

[email protected]

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mailto:[email protected]

Table of ContentsPreface..................................................................................................................................iTable of Contents...............................................................................................................iiiList of Tables.......................................................................................................................vList of Figures.....................................................................................................................viIntroduction..........................................................................................................................1

Impact of Container Design on People with Arthritis.....................................................2Tasks Associated with Spray Container Usage...............................................................2Spray Container Components and Variations..................................................................5

Outer Packaging...........................................................................................................6Container Body............................................................................................................7Closure.........................................................................................................................7Instructions and Labels................................................................................................7Dispensing System.......................................................................................................8

User Characteristics...........................................................................................................10Types of Arthritis...........................................................................................................11

Osteoarthritis..............................................................................................................11Rheumatoid Arthritis.................................................................................................12

Evaluation Methodologies.................................................................................................14Ease of Use Issues and Potential Solutions.......................................................................17

What are the issues associated with grasping and lifting a spray container?................18The spray container is too large to be gripped comfortably with adequate force......18The spray container is too small to be gripped comfortably with adequate force.....22The spray container may slip in the user’s hand........................................................23

What are the issues associated with instructions and labeling?.....................................25The text and graphics are difficult to see...................................................................25The text is difficult to find.........................................................................................26The expiration date is difficult to find, read, or interpret..........................................28

What are the issues associated with removing the outer packaging?............................30Removal of the outer safety seal requires the use of a tool.......................................30The outer safety seal does not provide a sufficient gripping surface........................33The box in which the product is packaged does not have a flap or tab to aid in opening......................................................................................................................36

What are the issues associated with removing the closure?..........................................38Grasping and removing the closure may require too much force..............................38The diameter and height of the closure prevents a strong grasp................................40

What are the issues associated with removing the sprayer head?.................................41Removing a factory sealed sprayer head may require too much force......................41Removing a continuous thread sprayer head may be difficult after it has been tightened by a user.....................................................................................................43The sprayer head connector may slip in the user’s hand as he or she attempts to twist it.................................................................................................................................44The diameter and height of the sprayer head connector prevents a strong grasp......45The amount of angular rotation required to remove the sprayer head may be too great...........................................................................................................................46

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What are the issues associated with affixing the nozzle extension or adaptor?............47Inserting the nozzle extension straw into the orifice may require too much dexterity and fine motor control...............................................................................................47

What are the issues associated with adjusting the nozzle or actuator?..........................49The nozzle or actuator is too small to be easily grasped...........................................49

What are the issues associated with dispensing the contents?.......................................51The grip required to squeeze the trigger is too wide or too narrow...........................51The sprayer head is not designed for easy gripping..................................................53The actuator must be squeezed or depressed multiple times to dispense the desired volume of contents.....................................................................................................54The actuator is too small............................................................................................56

Design Guidelines..............................................................................................................57References..........................................................................................................................62

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List of TablesTable 1: Tasks associated with spray container usage.........................................................3Table 2: Hand anthropometry of non-disabled individuals (Sources: [9, 13, 23])............10Table 3: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).......................................................................................................................11Table 4: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).......................................................................................................................20Table 5: Relationships between maximum grip diameter and cylinder diameter for maximum grip force..........................................................................................................20Table 6: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).......................................................................................................................51Table 7: Relationships between maximum grip diameter and cylinder diameter for maximum grip force..........................................................................................................52Table 8: Ease of use guidelines for spray container design...............................................57

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List of FiguresFigure 1: An assortment of spray containers.......................................................................1Figure 2: Spray container components................................................................................6Figure 3: An assortment of closures for spray containers...................................................7Figure 4: Dispensing systems include the following: (a) pump, (b) aerosol spray, (c) fingertip, (d) stem, and (e) trigger.......................................................................................9Figure 5: Joints of the hand commonly affected by arthritis.............................................12Figure 6: Rheumatoid arthritis can cause deformation of the joints resulting in stiffness and restricted range of motion...........................................................................................13Figure 7: A user’s grip strength (left) and pinch strength (right) are measured................15Figure 8: The Wong-Baker FACES Pain Rating Scale.....................................................16Figure 9: The top half of the body of this soap pump dispenser is smaller in diameter to facilitate grasping...............................................................................................................19Figure 10: A rectangular container is easier to grip and hold............................................23Figure 11: To attract the user’s attention, signal words are a larger text size and bolded, and information is presented in an outline format.............................................................26Figure 12: The expiration date is not in close proximity to its label.................................28Figure 13: The expiration date is clearly labeled, easy to read, and easy to understand.. .29Figure 14: The spray container on the left does not indicate where the perforated strip is. The spray container on the right clearly points out the location of the perforated strip....31Figure 15: The tab to remove the plastic ring on this aerosol spray can is small and may be difficult to remove for individuals with arthritis...........................................................33Figure 16: The added texture on this spray container closure increases friction...............38Figure 17: The small size of the nozzle extension and orifice may be problematic for users with arthritis..............................................................................................................47Figure 18: The nozzle extension is permanently attached.................................................48Figure 19: The small size of the nozzle and actuator make them more difficult to grasp and rotate...........................................................................................................................49Figure 20: The rear support on this trigger spray bottle eliminates the requirement for tight grasping.....................................................................................................................53Figure 21: A power sprayer minimizes the number of actions a user must perform.........55Figure 22: A cap provides a larger surface area for users to press against when dispensing the product.........................................................................................................................56

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IntroductionAccording to the CDC’s Morbidity and Mortality Weekly Report, over 49 million American adults have been diagnosed with arthritis by a doctor [5]. Of these, 21 million Americans report that arthritis limits their daily activities in some way [5], and nearly 9 million Americans are disabled as a result of arthritis making it the most common cause of disability in the United States [4]. By 2030, it is expected that arthritis will affect an estimated 67 million American adults [5].

Many individuals with arthritis experience significant difficulty completing a variety of everyday tasks such as using spray bottles. The products under consideration in this monograph include trigger sprayers, fingertip sprayers, pump sprayers, and aerosol spray cans, which are collectively referred to as “spray containers” (see Figure 1). These products vary in size, weight, shape, texture, dispensing mechanism, and operating force requirements. Each of these design components affects the user’s experience with the product, especially users experiencing symptoms of arthritis. As a result, users with arthritis may be unable to use certain products or may experience considerable pain and difficulty during use. This monograph discusses aspects of spray container design that affect ease of use for individuals with arthritis.

Figure 1: An assortment of spray containers.

There are two primary reasons why a company may choose to design products that are considered arthritis-friendly. First, a considerable portion of the market share is

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composed of individuals with arthritis, which is the most common cause of functional physical limitations in the United States. For users with arthritis, ease of use can become a key market discriminator in a group of similar, competing products. Second, products that are easy to use for individuals with arthritis will also be easy to use to most of the rest of the population.

Impact of Container Design on People with ArthritisUsers with arthritis may frequently experience difficulty and pain when attempting to perform routine tasks such as operating spray containers. Beyond the difficulty and pain, users may also feel a sense of helplessness and a loss of independence. These negative feelings are likely to be directly associated with the product, and might reduce the chance that the product will be purchased again. Instead, the user may seek a competing product that appears to be easier to use. Furthermore, a tarnished product image might be extended to all products of the same brand, and a user might assume that all products of a given brand are equally difficult to use.

Whereas those products that are difficult to use may generate avoidance, products that are easy to use may generate loyalty to the product and brand. Such products may stand out in the user’s mind as notable exceptions to the daily frustrations of living with arthritis, and may help to restore a sense of independence.

Tasks Associated with Spray Container UsageTo assess ease of use, the interaction between the user and the product should not be thought of as a single operation. Instead, the interaction should be decomposed into distinct operations. In this manner, the ease or difficulty of each operation can be assessed individually, and specific recommendations for improvement can be provided. Tasks are identified in a structured analysis of all the users’ actions associated with product usage. This may be accomplished by observing individuals as they use the product in a naturalistic setting. It is often beneficial to observe more than one user, because some users might skip operations or perform them differently than other users. For example, some users might neglect a container’s instructions for opening. The

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results of the task analysis for spray container usage are shown in Each of the tasks in Each of the tasks in Each of the tasks in Each of the tasks in Error: Reference source not found may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusingon a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusingon a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusingon a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusingon a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance..

Each of the tasks in Each of the tasks in Each of the tasks in Each of the tasks in Each of the tasks in Error: Reference source not found may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider theease of all tasks, rather than focusing on a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusing on a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusing on a single task that may

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seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. maypresent difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusing on a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance. may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusing on a single task that may seem more salient than others. Below are descriptions of each task, and a brief introduction of the associated container characteristics that impact task performance.

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Table 1: Tasks associated with spray container usage.

1. Grasp and lift the spray container2. Review product labeling and instructions3. Remove the outer packaging and outer safety seal4. Remove the closure5. Remove the sprayer head6. Replace the sprayer head7. Adjust the nozzle or actuator to enable dispensing8. Affix nozzle extension or adaptor to nozzle9. Dispense the contents10. Remove nozzle extension or adaptor from nozzle11. Adjust nozzle or actuator to disable dispensing12. Replace the closure

Grasp and lift the spray container. For transport and use, spray containers must be grasped and lifted. In most cases this is a single handed operation, and the other hand is free to open the container, dispense the contents, or execute other related tasks. Grasping and lifting a spray container may be difficult if the container is heavy, large, or does not provide a good gripping surface. Individuals with arthritis may experience difficulty due to limited strength, dexterity, and range of motion. They may also experience pain as they attempt to extend inflamed joints beyond comfortable positions. As a result, some individuals with arthritis may be unable to use the product as intended by the manufacturer, or they may risk dropping the container.

Review product labeling and instructions. In order to safely and effectively use many products, users must be able to read safety information, expiration dates, and dosage instructions. This critical information must be noticeable and readable for all users. Older adults, many of whom have age-related arthritis symptoms, typically have decreased visual acuity. Therefore, older adults may have difficulty reading product labeling and instructions that are printed in small font or with poor contrast. Although this difficulty is not directly related to arthritis, it is an important consideration for a product’s overall ease of use. Failure to read instructions and labels might have notable consequences. For example, a user might misread warning information that is printed in small font, and then proceed to use a product in an unsafe manner. This could obviously lead to a tarnished brand image, or worse. Additionally, users may fail to read the instructions for opening and using the product and, as a result, experience unnecessary pain and difficulty.

Remove the outer packaging and outer safety seal. Outer packaging may consist of a box that encloses the spray container or plastic wrap encompassing the entire container or just the closure or sprayer head. Users can open a box by tearing it, peeling it open at a flap, or tearing off a perforated strip. These actions may be difficult for individuals with arthritis if excessive force is required and if the gripping surface is not adequate. The outer plastic wrapping on a container can sometimes be removed by tearing or by

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twisting the closure or sprayer head to break the seal. Again, the forces required for these actions influence ease of use. If the outer seal consists of a non-perforated plastic sheet, most individuals with arthritis can be expected to experience difficulty. Although these tasks are only performed once for each product, they can represent significant barriers to overall ease of use. They also might establish a poor first impression of the product. A user might be unlikely to purchase the product in the future if the experience is difficult or painful, or if he or she must resort to using a tool (e.g., scissors). Some spray containers feature a dispensing safety mechanism that must be removed prior to use. For example, some nasal aspirators have a plastic ring that prohibits the plunging action of the dispenser, and some aerosol cans have a plastic pull tab that tears a strip of plastic free from the base of the dispenser cap, allowing its removal. The act of peeling or prying may be difficult for individuals with arthritis if the tab or ring does not feature a sufficient gripping surface, or if the safety mechanism is bound too tightly to the container.

Remove and replace the closure. The closure prevents inadvertent dispensing of contents by providing a physical barrier to the nozzle or actuator. Typically, friction fit or snap on closures are used for spray containers. Removing the closure requires the user to grasp the closure and container and then pull the closure off of the container. Alternatively, some closures, such as for aerosol spray paint containers, require the user to insert a lever into an opening in order to pry the closure from the container. Other designs use tabs that provide a means for lifting the closure or a levered mechanism to facilitate removal of the closure. Individuals with arthritis often have difficulty applying the frictional force necessary to grasp a closure and remove it from the container. A poor gripping surface on the closure or spray container can add to the problem by requiring the user to exert excessive gripping force. After using the product, the consumer must press the closure back on to the container. Again, a tight fit between the closure and the container as well as a poor gripping surface may prevent users with arthritis from successfully returning the closure to the container.

Remove and replace the sprayer head. Some spray containers allow the user to fill or empty the container contents via a removable cap or nozzle (as with trigger and fingertip sprayers). Traditional cap design requires the user to tightly grasp the cap while twisting it. Individuals with arthritis often have difficulty performing simultaneous actions like grasping and twisting. This is particularly true if either one of the actions requires substantial strength. Factory sealed caps may require more torque than some individuals with arthritis can exert. A poor gripping surface on the cap or bottle can compound the problem by forcing the user to exert excessive gripping force. Certain containers may simply be impossible to open for some individuals with arthritis. The act of screwing a cap onto a container sometimes requires a bit of dexterity in order to align the cap threading with the bottle threading. Due to dexterity limitations, this action might be difficult for some individuals with arthritis if the cap is short and has a small diameter.

Adjust nozzle to enable and disable dispensing. Most trigger spray containers require the user to twist the nozzle from the OFF position to the SPRAY or STREAM position. For some pump spray containers, the pump may need to be twisted to the open position.

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Individuals with arthritis may find it difficult to twist the nozzle or pump if it does not have a sufficient gripping surface or requires excessive force to twist. The act of twisting the nozzle may also be difficult because the small size of the nozzle requires a degree of dexterity that individuals with arthritis may not possess.

Affix and remove nozzle extension. Some aerosol spray cans, such as lubricants and dusters for electronics have a detachable nozzle extension to allow users to dispense the product in hard to reach areas. Typically, the nozzle is a small plastic tube that is inserted into the orifice of the actuator. Individuals with arthritis may find it difficult to grasp the nozzle extension and insert it into the orifice due to dexterity limitations and poor fine motor control.

Dispense the contents. To dispense the contents of the spray container, users much either squeeze or depress the dispensing mechanism. Squeezing the trigger may be difficult for individuals with arthritis if the grip required is too large or too small. Fingertip sprayers and aerosol spray cans limit the amount of force users can exert on the actuator by preventing users from using more than one finger to depress the actuator. With aerosol spray cans, the contents are continuously dispensed as long as the actuator is depressed. Trigger and pump sprayers, however, often require the user to squeeze or otherwise activate the actuator multiple times to dispense the desired volume of contents.

Spray Container Components and VariationsMost spray containers consist of five principal components: the outer packaging, container body (can or bottle), cap/closure, labeling/instructions, and the dispensing system (see Figure 2). Each of these may impede easy usage by individuals with arthritis. The following sections describe the components and their common design variations.

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Figure 2: Spray container components.

Outer PackagingBroadly defined, the outer packaging may be a box in which the spray container is packaged or a shrink-wrapped seal. The wrap may encircle the cap, nozzle, actuator, or dispensing mechanism to disable operation of the spray container. Some plastic seals have a perforated strip that, when pulled, allows for easy removal of the seal. Others must be cut or torn, possibly requiring the use of a tool such as scissors or a knife.

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Container BodySpray containers differ from each other by virtue of their material composition, shape, surface texture, size, and weight. Aerosol spray cans are typically constructed of steel or aluminum, whereas other types of spray containers are typically made of plastic. Most plastic containers are cheap and durable, but unable to withstand the pressures required for aerosol delivery. Decorative sprayer containers may be constructed of thin metals or glass. Aerosol spray cans and fingertip sprayers are generally cylindrical with the dispensing mechanism located on one end, while many trigger sprayers are commonly produced in both cylindrical and flattened, oblong forms with a “pistol grip” at the top to facilitate handling.

ClosureClosures vary in size, shape, surface texture, material composition, operating force requirements, and opening mechanism (see Figure 3). Closures for spray container containers are almost always composed of plastic. The closure may be friction fit or snap on that can be pulled off without requiring any twisting. Some closures, such as for aerosol spray paints, require the user to insert a lever, such as a screwdriver, into an opening in order to pry the closure from the container. Other designs provide a tab or a levered mechanism to facilitate removal of the closure. In general, trigger spray containers do not have a closure.

Figure 3: An assortment of closures for spray containers.

Instructions and LabelsInstructions and labels may be required for safe and proper usage of a product. Instructions are comprised of both text and graphics and include such things as opening instructions, dosage information, and instructions for usage. Labels include warnings, such as hazard and safety precautions and expiration dates. Common to all instructions and labels, the issues of font size and contrast are important. Small font and poor contrast can make it difficult for users to find and read information.

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Dosage information and instructions for use are particularly important for safe and proper usage of a product. Recommended doses can be displayed in either paragraph or table format. Typically, this information is made more salient by using a prominent title and by separating it from other text on the spray container. Warning labels alert users of the dangers associated with a product. Similar to dosage information, warnings can be set apart using spacing and prominent titles so as to make the information easier to find.

Expiration dates are also important for safe and proper usage of a product. A user who fails to notice an expiration date on an expired product may proceed to use a product that no longer meets the manufacturer’s standards, or that may even be unsafe for consumption. Expiration dates are often placed in obscure locations where users are unlikely to see them, even if actively searching. The date may be printed directly on a spray container. The text is often small, with poor contrast to the background. The format of the date is also important for identification and comprehension. The date may be preceded by the words “use by,” “best before,” or “expiration.”

Dispensing SystemAll dispensing systems for spray containers require the user to either squeeze or depress a control (see Figure 4). Trigger dispensers require users to grasp the container at the neck or head and squeeze the trigger. Only a small amount of the contents are dispensed with each squeeze of the trigger. Pump dispensers require users to press down on the actuator with either the fingers or the palm of the hand. Again, only a small amount of the contents are dispensed each time the actuator is depressed. Some pump dispensers, such as nasal sprays, require users to press down on the top of the container below the orifice while supporting the bottom of the container. Aerosol spray cans require users to either depress the actuator or, in the case of products such as whipped cream, displace the stem. Unlike trigger and pump dispensers, the contents of aerosol spray cans are continuously dispensed as long as the actuator is depressed or the stem is displaced.

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Figure 4: Dispensing systems include the following: (a) pump, (b) aerosol spray, (c) fingertip, (d) stem, and (e) trigger.

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User CharacteristicsThe design of products that are intended for use by individuals with arthritis should be guided by anthropometric data and by an understanding of the functional limitations associated with arthritis. Arthritis is a term used to describe painful inflammation of the joint or joints. The disability has many causes, and there are over 100 types of arthritis. Inflammation causes a reduction in tactile sensation and range of movement with a corresponding loss of dexterity and mobility. Arthritis is the greatest contributor to mobility and dexterity limitations, the largest category of functional limitations. As noted by TIA access (1996) [27], “Individuals have difficulty reaching things and doing complex or compound manipulations such as pushing while turning or pressing several buttons simultaneously. Twisting motions may be especially difficult. For individuals with arthritis, controls that require pinching or rotating are difficult to operate. In addition, individuals who are functionally limited are unable to exert as much force on controls as individuals without functional limitations. Individuals with poor muscle control may find it difficult to make fine motor movements with their fingers and may be restricted to gross movements with their hand(s).”

Anthropometric data might provide useful guidance for the design of containers for users with arthritis. There exists only a limited amount of anthropometric data on individuals with arthritis. However, hand dimensions may not differ significantly between individuals with and without arthritis [14], except for instances in which arthritis causes deformation of the bones and joints (e.g., rheumatoid arthritis). These deformities may prevent a user’s hand from fully encircling a closure or bottle. Table 2 shows anthropometric data for individuals without arthritis. The data were compiled from several sources [9, 13, 23]. These include measurements from British adults aged 19-65 years [13], and from British adults of unspecified age [9, 23].

Table 2: Hand anthropometry of non-disabled individuals (Sources: [9, 13, 23]).Dimension Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Hand lengthMale 173-175 178-189 205-209

Female 159-160 167-174 189-191

Palm lengthMale 98 107 116

Female 89 97 105

Thumb lengthMale 44 51 58

Female 40 47 53

Thumb breadthMale 11-12 23 26-27

Female 10-14 20-21 24

Index finger lengthMale 64 72 79

Female 60 67 74

Hand breadthMale 78 87 95

Female 69 76 83-85

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Table 3 shows maximum grip diameters for individuals with and without dexterity disabilities [9]. Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp with contact between the thumb and middle finger.

Table 3: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Non-disabled Male 45 52 59

Female 43 48 53

Dexterity-disabled Male 34 40 47

Female 34 40 48

Maximum grip diameter is of particular importance for usage of containers. Users with arthritis may experience considerable pain when forcibly grasping an object with a wide grip, in great excess of their maximum grip diameter. Hand breadth should also be taken into consideration when designing the height of a container. If the container spans the entire breadth of the hand (or more), then the user can distribute gripping force across the whole palm and all four fingers.

Types of ArthritisThe term “arthritis” is used to refer to over 100 different diseases that affect the joints of the body and the areas surrounding the joints. The most common types of arthritis are osteoarthritis and rheumatoid arthritis. Osteoarthritis is typically associated with the wear and tear of affected joints and is most prevalent in older adults. Rheumatoid arthritis can affect younger adults and even children, and is associated with inflammation of the lining of the joints. Other types of arthritis include fibromyalgia, gout, ankylosing spondylitis, and scleroderma.

OsteoarthritisOsteoarthritis (OA) is characterized by the deterioration of cartilage in the joints. Healthy cartilage cushions adjacent bones and allows for easy joint movement. Thus, the deterioration of cartilage causes bones to rub against each other, leading to stiffness, swelling, pain, and restricted range of motion. In the final stages of OA, bits of bone may float freely within the joint, and the lining of the joint (synovium) becomes inflamed [1].

Symptoms of osteoarthritis are more common in some joints than others. The base of the thumb and the distal finger joints are most commonly affected [1]. These joints are used in many interactions with spray container containers. Distal finger joints are heavily involved in certain pinch grips, such as that used to pinch and grasp the closure on a small finger spray container. They may also be used when puncturing an inner seal with the tip of the finger, grasping a large container or closure, or squeezing a trigger. The thumb is involved with all grip types, and nearly all manual interactions with spray containers. When gripping large spray containers or closures, users may experience pain in the base of the thumb as they adopt a wide grip. However, pain may also be experienced with smaller grips, such as those used to pinch a safety seal or to remove a small closure.

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Figure 5: Joints of the hand commonly affected by arthritis.

Symptoms are less common in the proximal interphalangeal joints (middle joint; approximately 35% of individuals with OA), and even less common in the metacarpophalangeal joints (base of the fingers; approximately 15% of individuals with OA) [1]. These joints are involved in pinching tabs and gripping containers and closures.

Wrists, which are affected in 20% of men with OA and only 5% of women [1], are involved in lifting and twisting actions. Symptoms are typically symmetric, meaning that symptoms in one hand are often accompanied by symptoms in the other hand [7]. Thus, many users may not be able to avoid pain by simply switching hands. A particularly problematic action for individuals with arthritis in the wrists is the act of twisting open a tightly secured closure. This can be painful for some users, and simply impossible for others.

Rheumatoid ArthritisRheumatoid arthritis (RA) is characterized by inflammation and swelling of the joints accompanied by pain and restricted range of motion [2]. More advanced RA causes deformation of the joints, which can prevent natural movements such as straightening the fingers (see Figure 6). Stiffness and restricted range of motion may cause individuals to adopt different strategies when using a product. For example, restricted wrist movement may force one to use several small movements to twist open a closure rather than one or two large movements. Also, deformation of the finger joints may force users to adopt different grips (e.g., a lateral “key” pinch rather than a finger tip pinch).

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Figure 6: Rheumatoid arthritis can cause deformation of the joints resulting in stiffness and restricted range of motion.

Symptoms of rheumatoid arthritis commonly appear first in the smaller joints of the body [2]. RA often affects the wrist joints and the finger joints closest to the hand (the metacarpophalangeal joints). Pain and swelling in these joints interferes with one’s ability to grip and twist objects, especially those that are large. Like OA, symptoms of RA are often symmetric, affecting the same joints on both sides of the body [2, 19]. Thus, many users may not be able to simply switch hands to avoid pain.

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Evaluation MethodologiesThere are two basic methods of acquiring information about human performance: direct measurement and derived assessment. If the goal is to evaluate the ability of a specific individual to use a product, then he or she is given a series of tasks to complete, and an evaluator observes performance. The tasks that are given to the user should be representative of the tasks associated with use of the product, as intended by the manufacturer, and it should be comprehensive. A list of tasks may be generated by a task analysis, which may involve observing several users as they interact with the product. By observing several users, rather than just one, the observer is more likely to capture all tasks associated with the product.

Direct Measurement. The direct measurement approach allows the collection of detailed data about the ability of a single individual to interact with a given product, although the findings may not generalize to a larger population. More robust direct measurement studies adopt effective population sampling strategies. By testing a diverse and representative group of users, the evaluator can generalize findings to a larger population segment with much better accuracy. Effective sampling for ease of use evaluations for people with arthritis can be very challenging. One must consider the variety of functional abilities and limitations within the population of individuals with arthritis. For example, some users may have limited strength, but normal dexterity. Others may have normal strength, but may experience considerable pain when exerting force. Still others may have limited reaching and grasping capabilities. A user’s level of experience may also have a significant impact on the outcome of the evaluation. For example, experience with difficult inner safety seals may lead one to puncture the seal with a fingernail, rather than attempt to grasp the edge of the seal and peel it off. Therefore, it is necessary to obtain a reasonably large and diverse sample of the population to which the evaluator wishes to generalize.

Derived Assessment. Derived assessment methods, such as functional assessments, checklist evaluations, or expert inspections, do not seek to measure human performance directly. Instead, such techniques are used to determine the extent to which a product meets formal or informal guidelines that have been associated with desired usability objectives. A checklist evaluation, also known as a heuristic evaluation, is employed where a considerable body of knowledge exists about a specific domain of human performance relative to the product of interest [20]. For example, a significant amount of data has been collected on the grip and torque strengths of individuals with arthritis. These data can be used to determine whether a product’s force requirements are likely to exceed the capabilities of the population of interest. However, given the number of factors that affect the usability of a spray container (e.g., size and texture) and the wide variations of each factor, it may not be feasible to assess a product solely by its adherence to guidelines. Therefore, it is advisable to combine direct measurements with derived assessments.

Given the challenges of sampling from a diverse population and our somewhat limited knowledge of designing for people with arthritis, it is necessary to combine data from

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both direct measurement and derived assessment evaluation techniques to obtain the desired degree of confidence in the evaluation results. Gaps in our knowledge in designing for people with arthritis can be addressed by performing user testing. Similarly, the sampling issues associated with human performance testing for accessibility can be addressed by using the derived assessment results to eliminate the need to test some populations and focus the assessment on others.

A variety of evaluation techniques and methodologies are available to the evaluator interested in measuring ease of use for individuals with arthritis. For best results, a combination of objective and subjective measures should be used.

The first stage of the evaluation may be accomplished without user participation. The evaluator first performs a task analysis in order to identify the actions that are involved in using the product. Next, the evaluator measures the force required for each of the physical actions identified in the task analysis. For example, one may measure the torque required to initially open the factory-tightened sprayer head, and the linear force required to squeeze the dispensing trigger. Finally, the evaluator determines whether the product meets a pre-specified set of guidelines that are based on prior research.

The second stage of the evaluation involves user participation. The evaluator should obtain measurements of the relevant functional capabilities of each user, such as grip and pinch strengths (see Figure 7).

Figure 7: A user’s grip strength (left) and pinch strength (right) are measured.

Next, the evaluator may objectively measure the forces that each user is able to generate upon the container. This requires instrumentation of the container by, for example, affixing a torque meter to the base of the container and a connecting rod to the closure. Objective force measurements for each user may be compared against the forces that are required to use the product, as measured during the first stage of the evaluation. If a number of participants are unable to generate the required forces upon the instrumented container, then a significant portion of the population with arthritis may experience difficulty with the product.

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Next, the user is given an unopened, unmodified product, and is asked to perform the set of tasks identified in the task analysis. During each task, the evaluator observes performance and records any difficulty or problems that arise. After each task, the user may provide subjective feedback about the experience in a free response format, and in the form of an ease-of-use rating scale. Additionally, users are asked to report any pain experienced and rate the severity of their pain using the Wong-Baker FACES Pain Rating Scale (see Figure 8).

Figure 8: The Wong-Baker FACES Pain Rating Scale.

The evaluator should record all such data, allowing the users to focus their attention on the product. After all tasks are completed, users may be asked to rate their agreement with a series of statements about the product (e.g., “I can use this product without overexerting myself.”). Finally, the results of the evaluation should be documented in order to affirm or deny the product’s ease of use, and to provide recommendations to the manufacturer.

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Ease of Use Issues and Potential SolutionsSpray containers have a number of ease of use issues related to the following tasks:

Grasping and lifting the container Reviewing the product labeling and instructions Removing the outer packaging or outer seal Removing and replacing the closure Removing and replacing the sprayer head Affixing and removing the nozzle extension Adjusting the nozzle or actuator Dispensing the contents

The following sections contain detailed information about common ease of use issues for each of these tasks. Potential solutions to each issue are proposed, and relevant design guidelines are presented.

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What are the issues associated with grasping and lifting a spray container?The body of a spray container is grasped and lifted during regular use. The following tasks entail grasping and lifting the body of a spray container:

Transporting the product Reading instructions and labels Removing the outer packaging or outer seal Removing and replacing the closure or sprayer head Dispensing the contents

The spray container is too large to be gripped comfortably with adequate force.Detailed Description:Holding a large spray container requires the user to adopt a wide grip. Because individuals with arthritis often experience limited range of motion in affected joints, they may be unable to open their hands wide enough to grasp a large spray container. Furthermore, strength declines as a user’s grip widens beyond moderate flexion. This means that even if a user is able to stretch his or her hand to fit the spray container, he or she may be unable to grasp the spray container tightly enough to perform other operations.

The hand is most powerful when it is flexed moderately [24]. When the hand grips a smaller object, grip force is decreased due to inadequate contact with the object and shortening of the muscles. When the hand grips a larger object, grip force decreases due to a decrease in the finger flexor muscles’ moment arm. Furthermore, a larger grip places the thumb and fingers in opposition to one another rather than in opposition to the palm.

Potential Solutions:Provide grasp points that are narrower than the main body of the spray container. If the body of the spray container is too large to be comfortably grasped with adequate force, an indentation can provide a more narrow grasping point.

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Figure 9: The top half of the body of this soap pump dispenser is smaller in diameter to facilitate grasping.

Reduce the diameter of the spray container. Another solution is to simply decrease the diameter of the spray container. This can be done by increasing the height of the spray container while decreasing the diameter to preserve the volume. Alternatively, a company can manufacture spray containers of several different sizes from which users can choose the most appropriate size for them.

For maximum grip power, what is the optimal spray container diameter? The answer depends in part on the user’s hand size and maximum grip diameter, because wider grips are associated with decreased strength. Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp while maintaining contact between the thumb and middle finger. For non-disabled adults, maximum grip power can be exerted on cylinders with diameters approximately 10 mm (0.4 inches) smaller than the maximum grip diameter. Specifically, the average non-disabled adult can exert maximum grip power on a cylinder with a diameter of 40 mm (1.6 inches) [24], which is approximately 10 mm less than their median maximum grip diameter ([9]; see Table 4). This diameter allows the thumb and middle finger to slightly overlap and directly oppose the palm.

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Table 4: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).

Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Non-disabledMale 45 52 59

Female 43 48 53

Dexterity-disabledMale 34 40 47

Female 34 40 48

Note that the relationship between maximum grip diameter and optimal diameter for grip force is somewhat speculative, because the data on these two parameters were derived from two separate studies [9, 24]. A single, systematic study is needed to confirm this relationship. Assuming that such a relationship exists, however, we can infer the diameter of a spray container that should yield maximum grip power for dexterity-disabled adults, including those with arthritis. The median maximum grip diameter of dexterity-disabled adults is 40 mm (1.6 inches) (see Table 4). Therefore, they might be expected to exert maximum gripping force on 30 mm (1.2 inches) cylinders, in comparison to 40 mm cylinders for non-disabled adults (see Table 5). Although it might not be feasible to design spray containers with diameters of only 30 mm, these data highlight the importance of maintaining a small diameter at the location intended for grasping.

Table 5: Relationships between maximum grip diameter and cylinder diameterfor maximum grip force.

Median Maximum Grip Diameter (male & female)

(mm)

Diameter for Maximum Grip Force (mm)

Non-disabled 50 A 40 B

Dexterity-disabled 40 A 30 C

A: Source [9]; B: Source [24]; C: Inferred.

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Applicable Guidelines: Guideline: Ensure that the product is easy to grip and control. The shape of the

product should be easy to hold so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman & Rosenberg, 1991 [6]; Haigh, 1993 [15]

Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.Source: Steinfeld & Mullick, 1990 [26]

Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld & Mullick, 1990 [26]

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The spray container is too small to be gripped comfortably with adequate force.Detailed Description:Small spray containers can be just as problematic for users as large spray containers. Holding and manipulating a small spray container requires the user to have fine motor coordination and dexterity. Because individuals with arthritis often experience limited dexterity and fine motor coordination, they may find it difficult to securely hold a small spray container in their hands and perform tasks such as removing the closure and dispensing the contents.

Potential Solutions:Increase the diameter of the spray container. Just as decreasing the diameter of a large spray container can make the container more usable, increasing the diameter of a small spray container can also make the container easier to use for individuals with arthritis. This can be done by decreasing the height of the spray container while increasing the diameter to preserve the volume. Alternatively, a company can manufacture spray containers of several different sizes from which users can choose the most appropriate size for them.

Maximize friction between the spray container and the hand. Friction can be increased by adding texture to the surface of the container where users are most likely to grasp it. As a result, users will not have to grip the spray container with as much force.




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The spray container may slip in the user’s hand.Detailed Description:Individuals with arthritis typically have weaker grips than those without arthritis. A weakened grip may allow a spray container to slide in the hand as the user attempts to lift or manipulate the container. As a result, the user may experience difficulty performing such actions as lifting the spray container, removing the closure, adjusting the nozzle, and dispensing the product. Factors influencing the user’s ability to grasp a spray container include container size, container shape, surface texture, and material composition. The nature of the product and the environment in which it is used can magnify the effects of these factors. For example, users may experience more difficulty holding and manipulating a can of shaving cream in the shower due to humidity and moisture.

Potential Solutions:Increase friction between the spray container and the hand. Friction can be increased by adding texture to the surface of the container where users are most likely to grasp it.

Use a non-cylindrical shape for the spray container. Container slippage can be reduced by using a non-cylindrical container shape. The uniform contour of a cylinder allows it to slide easily in a weak grip. In contrast, elliptical and rectangular containers provide leverage points that can help reduce grip strength requirements.

Figure 10: A rectangular container is easier to grip and hold.

Applicable Guidelines:

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Guideline: Ensure that the product is easy to grip and control. The shape of the product should be easy to hold, so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman and Rosenberg, 1991 [6]; Haigh, 1993 [15]

Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.Source: Steinfeld and Mullick, 1990 [26]

Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [26]

Guideline: Provide a high friction grip surface on cylindrical containers. Tight grasping of the container is required to provide a counter-rotational force when removing a twist off cap. Provide a high friction surface on a cylindrical container to facilitate tight grasping.Source: GTRI

Guideline: Provide a non-cylindrical grip feature, such as grip indentions, or use a non-cylindrical container.Source: GTRI

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What are the issues associated with instructions and labeling?Instructions are defined as any textual or graphical information that tells the user how to operate or consume the product. This includes opening instructions, consumption instructions, and dosage information. Labels include warnings, product information, and expiration dates. The ease of use issues associated with instructions and labels are not unique to users with arthritis, but are common to all users. However, older adults, who comprise a large portion of the population with arthritis, often experience a decline in visual acuity. Therefore, the visual design of instructions and labeling are particularly important for many users with arthritis.

The text and graphics are difficult to see.Detailed Description:Some users may have difficulty reading text due to small text size or poor contrast with the background. Textual or graphical instructions for adjusting a nozzle are often printed directly on the nozzle using an inkless embossing process, resulting in very poor visual contrast. Additionally, because of limited space on containers such as nasal sprays for labeling, product designers may elect to use a smaller text size, resulting in reduced readability. Users that are unable to read the product labeling may use the product incorrectly or in an unsafe manner.

Potential Solutions:Enhance the readability of all text by increasing font size and contrast. Ideally, all text and graphics should be printed using high contrast ink and a large font size. Previous studies have indicated that 10-point type is perceived as more readable than smaller font sizes by both younger and older adults [25]. If instructions are printed using an inkless embossing process, the poor contrast should be compensated for by increasing the font size and increasing the depth of the embossment.

Provide full instructions either on the product’s outer packaging or as a product insert. If the size of the container prevents the use of a larger font size, provide only the most important warnings and instructions on the body of the spray container, and provide a supplement for the abbreviated product labeling. For example, if the product is packaged in a box, the complete set of instructions and warnings could be printed directly on the box or on a piece of paper as a package insert.

Applicable Guidelines: Guideline: Enhance readability and comprehension of labels, critical instructions,

and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.Source: GTRI

Guideline: It is essential that a warning be as salient as possible to capture the attention of users. The salience of a visual warning can be enhanced using large, bold print, high contrast, color, borders, and pictorial symbols.Source: Wogalter, Conzola, and Smith-Jackson, 2002 [30]

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The text is difficult to find.Detailed Description:Instructions and warnings may be difficult to find if they are not preceded by a prominent title or if they are placed in an unexpected location. For example, dosage information may be difficult to find if all of the product information runs together in a paragraph format.

Potential Solutions:Provide clearly visible, prominent titles for each section. Providing a title or signal word attracts the user’s attention and aids in visual search (see Figure 11). Titles or signal words are perceived as more readable when the difference in title and text size is two points (e.g., 12-point type for titles and 10-point type for text) [25].

Present product information in an outline format rather than as a continuous paragraph layout. Text that is presented as bullets in an outline format allows for faster visual search and maintains attention for a longer period of time (see Figure 11).

Figure 11: To attract the user’s attention, signal words are a larger text size and bolded, and information is presented in an outline format.

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Applicable Guidelines: Guideline: A warning should contain a signal word to attract the attention of the

user.Source: Wogalter, Conzola, and Smith-Jackson (2002) [30]

Guideline: To increase effectiveness and salience, warnings should be presented as bullets in an outline format.Source: Wogalter, Conzola, and Smith-Jackson (2002) [30]

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The expiration date is difficult to find, read, or interpret.Detailed Description:Expiration dates may be difficult to find if they are placed in an unexpected location or if they are not clearly labeled and cannot be distinguished from the lot number. Once the date is found, it may be difficult to read if it is printed in small lettering or with poor contrast. Often, the expiration date on the product’s box has no contrast at all because the date was printed using an inkless embossing process. Finally, the date may be misinterpreted if its format is ambiguous. For example, “12 07 11” could be interpreted as December 7, 2011 or July 12, 2011.

Figure 12: The expiration date is not in close proximity to its label.

Potential Solution:Print expiration dates using an unambiguous format, large font, and sufficient contrast. The expiration date should also be labeled appropriately so that it can be distinguished from the lot number. To help users in differentiating between the month and the year of an expiration date, the year should be displayed in the four digit format (e.g., 2011 rather than 11). The location of the expiration date should also be in close proximity to its label. Previous studies have indicated that 10-point type is perceived as more readable than smaller font sizes by both younger and older adults [25]. To enhance contrast, the

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expiration date should be printed using high contrast ink on a part of the container that is opaque.

Figure 13: The expiration date is clearly labeled, easy to read, and easy to understand.

Applicable Guideline: Guideline: Enhance readability and comprehension of labels, critical instructions,

and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.Source: GTRI

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What are the issues associated with removing the outer packaging?The outer packaging of a product is intended to protect product integrity and safety while providing evidence of tampering. It must be removed prior to the first usage of the product. Outer packaging typically consists of a box that encloses the spray container or a tamper-evident seal, referred to as the outer safety seal. The tamper-evident seal may be plastic wrapping on the closure of the container or a plastic ring around the closure preventing its removal. Because the outer packaging is intended to protect the product and provide evidence of tampering, it can be difficult to remove. Users with arthritis, in particular, may experience difficulty removing the outer safety seal or when opening the packaging. Although this action is only performed once for each item, it can represent a significant barrier to overall ease of use and may discourage users from future purchases.

Removal of the outer safety seal requires the use of a tool.Detailed Description:Tamper-evident plastic wrapping may not have a perforated strip, making it difficult for users to tear the seal and remove it. Instead, users must initiate a tear in the plastic with a tool such as a knife or scissors. The amount of force required to remove the plastic ring may outside of the functional abilities of users with arthritis prompting them to use a tool to remove the plastic ring. However, the use of tools can be problematic for three reasons. First, a tool may not be readily available, so the user may struggle to accomplish the task by hand before searching for a tool. Second, users with arthritis may experience pain in their fingers, hands, and wrists while using the tool. Pain may be caused by the grip required to hold the tool, or by the amount of force necessary to use the tool. Finally, users may resort to using the tool in an unsafe manner, which can lead to serious injury.

Potential Solution:Provide a clearly visible perforation in the plastic wrapping that will allow users to remove the seal by hand. Perforations in the plastic wrapping allow users to tear the plastic more easily. The perforations should be clearly evident by virtue of their placement and their visual contrast with the underlying material. Note that perforations in clear plastic may be difficult to see, particularly when covering a light-colored spray container. Perforations can be made more visible by using a dark plastic seal or by placing markings on the seal at the perforations (see Figure 14). In addition to being clearly visible, the edge of the seal at the perforation should be easy to grip.

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Figure 14: The spray container on the left does not indicate where the perforated strip is. The spray container on the right clearly points out the location of the perforated strip.


product should be easy to hold, so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman and Rosenberg, 1991 [6]; Haigh, 1993 [15]

Guideline: Provide at least one mode of operation that does not require fine motor control or simultaneous actions, and that is operable with limited reach and strength.Source: Section 508 1194.31(f) [12]

Guideline: Do not require the use of tools.Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).Source: GTRIDiscussion: Preliminary data collected during GTRI assessments of users with arthritis suggested that pinch force requirements should not exceed 3.0 pounds; however, further research is needed to validate this finding.

Guideline: Ensure that the proper method of removing the outer safety seal is clearly evident, either through the design of the safety seal or through instructions printed prominently on the packaging. For example, if the seal is removed by twisting the cap to break the seal, instructions like “Twist cap to break seal”

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should be provided. If the seal is removed by pulling a perforated strip, the strip should be clearly visible.Source: Vanderheiden, 1997 [28]Discussion: The steps required to open some containers may be intuitively obvious to most users and therefore may not require printed instructions.

Guideline: If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.Source: GTRI

Guideline: If the safety seal is removed in an independent action (e.g., by pulling a strip), the force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [12]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

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The outer safety seal does not provide a sufficient gripping surface.Detailed Description:Even if tamper-evident plastic wrapping has a perforated strip, users may experience difficulty grasping the strip and tearing it off. As a result, users may resort to using a tool to remove the outer safety seal, possibly in a dangerous manner. The outer plastic ring may also be difficult to grasp if the tab does not have a sufficient grasping surface or if the tab is too small. Users may be prompted to remove the outer safety seal using a sharp tool such as scissors or a knife. However, the use of tools can be problematic for three reasons. First, a tool may not be readily available, so the user may struggle to accomplish the task by hand before searching for a tool. Second, users with arthritis may experience pain in their fingers, hands, and wrists while using the tool. Pain may be caused by the grip required to hold the tool, or by the amount of force necessary to use the tool. Finally, users may resort to using the tool in an unsafe manner, which can lead to serious injury.

Potential Solution:Provide a large tab on the outer safety seal with a sufficient gripping surface that can be removed with less than 5 pounds of force. If a smooth, non-textured tab is provided, it should be at least 0.47 inches (12 mm) wide by 0.79 inches (20 mm) long so that users can grasp it between the thumb and lateral aspect of the index finger. Smaller tabs may be difficult to grasp and may slide from users’ fingers, especially if the tabs are not textured. The optimal pull tab would be large, located on the edge of the seal, with a textured surface that reduces slippage (e.g., a foil tab with raised bumps). The amount of force required to peel the seal away from the container should not exceed 5 lbs (22.2 N).

Figure 15: The tab to remove the plastic ring on this aerosol spray can is small and may be difficult to remove for individuals with arthritis.



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Guideline: Do not require the use of tools.Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).Source: GTRIDiscussion: Preliminary data collected during GTRI assessments of users with arthritis suggested that pinch force requirements should not exceed 3.0 pounds; however, further research is needed to validate this finding.

Guideline: Ensure that the proper method of removing the outer safety seal is clearly evident, either because of the design of the safety seal or because of instructions printed prominently on the packaging. For example, if the seal is removed by twisting the cap to break the seal, instructions like “Twist cap to break seal” should be provided. If the seal is removed by pulling a perforated strip, the strip should be clearly visible.Source: Vanderheiden, 1997 [28]Discussion: The steps required to open some containers may be intuitively obvious to most users and therefore may not require printed instructions.

Guideline: If the safety seal is removed in an independent action (e.g., by pulling a perforated strip), the force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [12]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

Guideline: Provide texture on the grasp point that facilitates gripping the tab. The grasp point should be textured with a series of bumps or raised strips that are perpendicular to the peel direction.Source: Department of Trade and Industry, UK, 2003 [10]

Guideline: Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For

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example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the finger.Source: Pirkl, 1995 [22]Discussion: By allowing redundant modes of operation, users might have the option to avoid using joints in which swelling and pain are most severe.

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The box in which the product is packaged does not have a flap or tab to aid in opening.Detailed Description:A box can be difficult to open if its opening flap does not have a tab for users to grasp. Flaps without a sufficient grasping surface must be picked at with a tool or a fingernail until there is a large enough area for the user to grasp. This may be difficult for users with arthritis because it requires relatively fine motor control. A user might simply tear the box open by inserting a finger under the flap’s edge, but the force required to do so might cause pain for users with arthritis.

Potential Solutions:Provide a perforated strip that users can easily peel off. A perforated strip can be peeled away easily, provided that the force required is not excessive (less than 5 lbs (22.2 N)). The end of the strip should have a sufficiently large tab for grasping.

Provide a large tab under which the user can insert a finger. If a tab is provided with no perforated strip, the tab should be large enough to accommodate most of the tip of the finger. The force required to pull open the tab should not exceed 5 lbs (22.2 N).

Applicable Guidelines: Guideline: If the safety seal is removed in an independent action (e.g., by pulling

a perforated strip), the force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [12]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

Guideline: If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).Source: GTRIDiscussion: Preliminary data collected during GTRI assessments of users with arthritis suggested that pinch force requirements should not exceed 3.0 pounds (13.3 N); however, further research is needed to validate this finding.

Guideline: Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For

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example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the finger.Source: Pirkl, 1995 [22]Discussion: By allowing redundant modes of operation, users might have the option to avoid using joints in which swelling and pain are most severe.


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What are the issues associated with removing the closure?To remove a friction fit or snap on closure, users must grip the spray container in one hand while tightly gripping and pulling up on the closure with the other hand. Following is a discussion of issues related to the usability of friction fit and snap on closures.

Grasping and removing the closure may require too much force.Detailed Description:Many individuals with arthritis experience pain and difficulty removing the closures on some spray containers. When the closure is tightly secured to the spray container, users’ fingers may slip off of the closure as they attempt to pull the closure off. To prevent slippage, users may be required to exert considerable grip force. Users with arthritis typically have weaker grip strengths, so they are more likely to experience problems with closures slipping in their hands. Factors influencing the user’s ability to grasp a friction fit or snap on closure include the size, shape, surface texture, and material composition of the closure. The nature of the product and the environment in which it is used can magnify the effects of these factors. For example, users may experience more difficulty removing the closure on a can of shaving cream in the shower due to humidity and moisture.

Potential Solution:Increase friction between the closure and the hand. Friction can be increased by adding texture to the surface of the container where users are most likely to grasp it.

Figure 16: The added texture on this spray container closure increases friction.



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Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [26]

Guideline: Provide a high friction grip surface on cylindrical containers. Tight grasping of the container is required to provide a counter-rotational force when removing a twist off cap. Provide a high friction surface on a cylindrical container to facilitate tight grasping.Source: GTRI


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The diameter and height of the closure prevents a strong grasp.Detailed Description:The size of the closure, both in diameter and height, greatly affects how tightly users can grasp it. Very large diameter closures afford weak grips because the fingers are weaker when they are near full extension [24]. Likewise, closures with very small diameters afford weak grips due to muscle shortening. Small diameter closures also require users to have sufficient dexterity and fine motor control in their hands.

In addition to the diameter, the height of a closure affects how tightly users can grasp it. Short closures, such as those less than 0.5 inches, may be difficult to grasp for users with arthritis due to the requirement for dexterity. Additionally, users may find it difficult to adopt the hand position necessary to grasp the closure. A shorter closure limits the variety of possible hand positions users can adopt when grasping and removing closures. Taller closures allow for more flexibility in how the user grasps the closure.

Potential Solutions:Use a moderate closure diameter. Because the hand is most powerful when it is moderately flexed [24], the diameter of closures should be determined by the user’s grip span when the hand is moderately flexed. For non-disabled individuals, maximum force can be generated on closures with diameters between 1 and 3 inches (25-75 mm) [21]. This is a relatively wide range, and users with arthritis may experience pain at the extremes, so more moderate closure diameters are preferable (e.g., between 1.5 and 2 inches).

Increase the height of the closure. Increasing the surface contact between the fingers and the closure by increasing the height of the closure allows users to grasp the closure with more force and greater ease. More laboratory testing is required to determine the optimal height of a closure.

Applicable Guidelines: Guideline: Require a grip span of no more than 2.8 inches (71 mm) for products

that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [26]Discussion: This guideline applies to a standard power grip (like grasping a cylinder) and may not be directly applicable to the key pinch grip commonly used to grasp a closure.


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What are the issues associated with removing the sprayer head?Users may want to remove the sprayer head of a spray container to refill the contents. The sprayer head attaches to the body of the spray container with a continuous thread closure. To remove a continuous thread closure, users must grip the spray container in one hand while tightly gripping and applying rotational force to the closure with the other hand. Grasping the closure while simultaneously rotating it may be especially difficult for some individuals with arthritis. Additionally, because the sprayer head prevents users from approaching the closure from the top, users are limited in the type of grip they can use when grasping the closure. Following is a discussion of issues related to the usability of continuous thread closures.

Removing a factory sealed sprayer head may require too much force.Detailed Description:Many individuals with arthritis experience pain and difficulty exerting the amount of force required to remove the sprayer head on some continuous thread sprayer heads. The factory sealed continuous thread closures that have been tested at the GTRI Accessibility Evaluation Facility have required from 1 pound-inch of torque to over 20 pound-inches of torque to remove. In laboratory tests conducted at GTRI with a variety of closure designs, individuals with arthritis have typically been able to exert approximately 2 to 30 pound-inches of torque on the closures before experiencing pain. This wide range is the result of differences among the functional abilities of the participants and variations in closure design.

When a high amount of torque is required to remove a sprayer head, high grip force is also required. In order to prevent a sprayer head from slipping in the hand, the user must apply sufficient grip force. Thus, users with arthritis may experience pain in the wrist as they apply torque and in the hand and fingers as they apply grip force.

Potential Solution:Limit the amount of torque that is required to remove a factory sealed sprayer head to 10 pound-inches (1.1 N-m) or less. To make a sprayer head easier to remove, the amount of torque required to remove it must be decreased. However, product safety and integrity must also be considered. To accommodate approximately 90% of users with arthritis, torque requirements should not exceed 10 pound-inches (1.1 N-m) for sprayer head connectors that are at least one inch in diameter. Reducing the diameter of the sprayer head connector to less than one inch also reduces the amount of torque that a user can exert, so the maximum torque requirement is lower for smaller sprayer head connectors. Reducing the amount of torque necessary to rotate the sprayer head connector also reduces the amount of grip force that is required to prevent the closure from slipping in the hand.

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Applicable Guidelines: Guideline: Minimize rotational force required to remove the cap from the factory

sealed position.Sources: Berns, 1981 [3]; Langley, Janson, Wearn, and Yoxall, 2005 [18]; Voorbij and Steenbekkers, 2002 [29]


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Removing a continuous thread sprayer head may be difficult after it has been tightened by a user.Detailed Description:After the initial opening, a continuous thread sprayer head can be retightened with a variable amount of torque, and this may affect the ease of future openings. Hence, even if a factory sealed sprayer head is easy to open for a user with arthritis, it may be difficult on subsequent uses. A friend or family member might tighten the sprayer head too much, or an individual with arthritis might tighten it too much on a day when he or she is not experiencing severe symptoms. Symptoms of arthritis can vary dramatically on a daily basis, as can the individual’s functional abilities.

Potential Solution:Use steep threading rather than shallow threading. The tendency for users to over tighten a sprayer head might be reduced by using steep threading (causing the sprayer head connector to rise more rapidly as it is unscrewed). Preliminary testing at GTRI with six different continuous thread closures and containers suggests that closures with steep threading cannot be tightened onto the bottle as tightly as those with shallow threads. After tightening closures with 15 pound-inches (1.7 N-m) of torque, those with steep threading (average incline 4.5°) required approximately 33% less torque to open than those with shallow threading (average incline 1.8°).

Applicable Guideline: Guideline: Provide at least one mode of operation is that does not require fine

motor control or simultaneous actions, and that is operable with limited reach and strength.Source: Section 508 1194.31(f) [12]

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The sprayer head connector may slip in the user’s hand as he or she attempts to twist it.Detailed Description:When a sprayer head is tightly secured to a container, users’ hands may slip around the sprayer head connector as they attempt to twist it. To prevent slippage, users may be required to exert considerable grip force on the sprayer head connector while simultaneously twisting it. Users with arthritis typically have weaker grip strengths, so they are more likely to experience problems with sprayer head connectors slipping in their hands.

Potential Solution:Reduce the required grip force by increasing the friction between the sprayer head connector and the hand. A common method of increasing friction is to incorporate ridges or serrations into the closure’s surface. These should be large (deep and wide) enough to provide friction, but not so wide as to produce discomfort on the skin. Surface friction can also be introduced by using different types of materials other than plastic. For example, an elastomeric surface coating can provide excellent grip.



Guideline: Avoid sharp edges. Knurls on twist-off closures should be rounded.Source: GTRI


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The diameter and height of the sprayer head connector prevents a strong grasp.Detailed Description:The size of the sprayer head connector, both in diameter and height, greatly affects how tightly users can grasp it. Very large diameters afford weak grips because the fingers are weaker when they are near full extension [24]. Likewise, very small diameters afford weak grips due to muscle shortening. Small diameter sprayer head connectors also require users to have sufficient dexterity and fine motor control in their hands.

In addition to the diameter, the height of a closure affects how tightly users can grasp it. Short closures, such as those less than 0.5 inches, may be difficult to grasp for users with arthritis due to the requirement for dexterity. Additionally, users may find it difficult to adopt the hand position necessary to twist the sprayer head connector, especially since the sprayer head prevents users from grasping the connector from the top. A shorter height limits the variety of possible hand positions users can adopt when grasping and twisting the connector whereas a taller height allows for more flexibility.

Potential Solutions:Use a moderate diameter for the sprayer head connector. Because the hand is most powerful when it is moderately flexed [24], the diameter of sprayer head connectors should be determined by the user’s grip span when the hand is moderately flexed. For non-disabled individuals, maximum force can be generated on container closures with diameters between 1 and 3 inches (25-75 mm) [21]. This is a relatively wide range, and users with arthritis may experience pain at the extremes, so more moderate diameters are preferable (e.g., between 1.5 and 2 inches).

Increase the height of the sprayer head connector. Increasing the surface contact between the fingers and the sprayer head connector by increasing the height of the connector allows users to grasp the closure with more force and greater ease. More laboratory testing is required to determine the optimal height of a sprayer head connector.

Applicable Guidelines: Guideline: Require a grip span of no more than 2.8 inches (71 mm) for products

that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [26]Discussion: This guideline applies to a standard power grip (like grasping a cylinder) and may not be directly applicable to the palmar pinch commonly used to grasp the sprayer head connector.


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The amount of angular rotation required to remove the sprayer head may be too great.Detailed Description:Some sprayer head connectors require a large degree of rotation to remove from the container (e.g., 270° of rotation). Because many individuals with arthritis are limited in their range of motion in the hands and wrists, they must make several small movements rather than a few large movements to remove the sprayer head from the container. If rotating the sprayer head connector slightly causes pain or discomfort for users with arthritis, then the product may not be usable if several small rotations are required to remove the sprayer head.

Potential Solution:Use a steep and short threading so that the sprayer head can be removed with a limited amount of rotation. Ideally, removing a sprayer head should require no more than a quarter turn. This can be accomplished by using a steep and short threading design which allows the sprayer head connector to rise rapidly from the container as it is rotated.

Applicable Guidelines: Guideline: Screw top caps should fit in the hand. Their removal should require

no more than ¼ turn for each angular movement, and no more than two angular movements should be required.Source: Haigh, 1993 [15]

Guideline: Minimize user actions.Source: HFDS 2.6.8 [11]

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What are the issues associated with affixing the nozzle extension or adaptor?Some aerosol spray cans have a detachable nozzle extension so that the product can be dispensed in hard to reach areas. The nozzle extension is typically a small plastic tube that is inserted into the orifice of the nozzle. Affixing the nozzle extension to the orifice on the nozzle may require great dexterity and fine motor control, especially if the extension tube and the orifice have a small diameter.

Inserting the nozzle extension straw into the orifice may require too much dexterity and fine motor control.Detailed Description:Nozzle extensions typically have a very small diameter. For example, the nozzle extension for many brands of canned air used for removing dust from computers is only 0.09 inches (2.3 mm) in diameter. Users with arthritis often experience limited dexterity and fine motor control in their hands and may have difficulty grasping the nozzle extension. Even if users are able to pick up the nozzle extension, they may be unable to insert the straw into the orifice due to dexterity and fine motor control limitations.

Figure 17: The small size of the nozzle extension and orifice may be problematic for users with arthritis.

Potential Solutions:Provide a grasping point on the nozzle extension. Adding grasping features, such as increasing the diameter of a small section of the nozzle extension or adding texture to the straw can assist users in picking up the nozzle extension. However, it may still be difficult to insert the nozzle extension into the orifice.

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Affix the nozzle extension to the nozzle permanently. These tasks can be eliminated if the nozzle extension is permanently affixed to the nozzle. For example, the nozzle extension in Figure 18 is permanently attached to the spray can but still allows users to dispense the product as a spray or as a concentrated stream through the nozzle extension straw.

Figure 18: The nozzle extension is permanently attached.





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What are the issues associated with adjusting the nozzle or actuator?Non-aerosol spray containers typically require the user to adjust the nozzle or actuator to enable dispensing of the product. Some spray containers also allow users to adjust the spray in this manner. To adjust the nozzle or actuator, users must first identify the correct setting and then rotate the nozzle or actuator to that setting.

The nozzle or actuator is too small to be easily grasped.Detailed Description:Users with arthritis may experience difficulty grasping the nozzle or actuator if it is too small or if it lacks surface texture. Individuals with arthritis often experience limitations in dexterity and fine motor control making it difficult to manipulate small objects.

Figure 19: The small size of the nozzle and actuator make them more difficult to grasp and rotate.

Potential Solutions:Increase the size of the nozzle or actuator. Increasing the surface contact between the fingers and the nozzle or actuator by increasing its size allows users to grasp the nozzle or actuator with more force and greater ease.

Increase friction between the hand and the nozzle or actuator. Adding texture to the surface of the nozzle or actuator help to reduce the grip force required to rotate it. Texture can be added by incorporating ridges or serrations or by using different types of materials. An elastomeric surface coating provides excellent grip and is also comfortable on the user’s hand.

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What are the issues associated with dispensing the contents?To dispense the contents of a spray container, users must either squeeze or depress an actuator with sufficient force to activate the valve or pump. The amount of force that users are able to exert when dispensing the contents of a spray container can be facilitated or reduced depending on several features of the dispensing system such as the grip required and the size of the area being depressed.

The grip required to squeeze the trigger is too wide or too narrow.Detailed Description:Because individuals with arthritis often experience limited range of motion in affected joints, they may be unable to open their hands wide enough to grasp and squeeze a trigger dispenser. Additionally, because strength declines as a user’s grip widens beyond moderate flexion, individuals with arthritis that are able to open their hands wide enough may not be able to exert enough grip force to successfully squeeze the trigger and dispense the contents. Likewise, when the hand grips a smaller object, grip force is decreased due to inadequate contact with the object and shortening of the muscles.

Potential Solution:Limit the minimum and maximum grip size required to squeeze the trigger. Reducing the grip size necessary to squeeze the trigger allows users with reduced strength and range of motion to successfully operate the spray container. Alternatively, a company can manufacture the product in several different sizes so that users can select the size that best fits them.

For maximum grip power, what is the optimal spray container diameter? The answer depends in part on the user’s hand size and maximum grip diameter, because wider grips are associated with decreased strength. Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp while maintaining contact between the thumb and middle finger. For non-disabled adults, maximum grip power can be exerted on cylinders with diameters approximately 10 mm (0.4 inches) smaller than the maximum grip diameter. Specifically, the average non-disabled adult can exert maximum grip power on a cylinder with a diameter of 40 mm (1.6 inches) [24], which is approximately 10 mm less than their median maximum grip diameter ([9]; see Table 6). This diameter allows the thumb and middle finger to slightly overlap and directly oppose the palm.

Table 6: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [9]).

Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Non-disabledMale 45 52 59

Female 43 48 53

Dexterity-disabledMale 34 40 47

Female 34 40 48

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Note that the relationship between maximum grip diameter and optimal diameter for grip force is somewhat speculative, because the data on these two parameters were derived from two separate studies [9, 24]. A single, systematic study is needed to confirm this relationship. Assuming that such a relationship exists, however, we can infer the diameter of a spray container that should yield maximum grip power for dexterity-disabled adults, including those with arthritis. The median maximum grip diameter of dexterity-disabled adults is 40 mm (1.6 inches) (see Table 6). Therefore, they might be expected to exert maximum gripping force on 30 mm (1.2 inches) cylinders, in comparison to 40 mm cylinders for non-disabled adults (see Table 7). Although it might not be feasible to design spray containers with diameters of only 30 mm, these data highlight the importance of maintaining a small diameter at the location intended for grasping.

Table 7: Relationships between maximum grip diameter and cylinder diameterfor maximum grip force.

Median Maximum Grip Diameter (male & female)

(mm)

Diameter for Maximum Grip Force (mm)

Non-disabled 50 A 40 B

Dexterity-disabled 40 A 30 C

A: Source [9]; B: Source [24]; C: Inferred.




Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld & Mullick, 1990 [26]

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The sprayer head is not designed for easy gripping.Detailed Discussion:Squeezing the trigger while holding and maintaining control over the spray container may be difficult for users with arthritis if the design of the sprayer head and trigger do not facilitate grasping. Additionally, squeezing the trigger may cause pain for users with arthritis if the shape of the trigger creates pressure points on inflamed joints, especially if users must exert considerable force to squeeze the trigger. Sharp edges can cause additional pain and prevent users from squeezing the trigger with enough force to dispense the contents of the spray container.

Potential Solutions:Maximize friction between the trigger and the user’s hand. Friction can be increased by adding texture to the surface of the trigger. One of the most effective methods for adding friction is by adding an elastomeric coating to the trigger. Not only does the elastomeric coating increase friction but it also provides a comfortable surface for users to place their hand.

Provide a contoured grip. One way to avoid sharp edges is to design the trigger with a contoured grip that follows the shape of a user’s hand. A contoured grip will also help prevent the user’s hand from slipping off of the trigger.

Reduce the grip force required to hold and maintain control over the container. The amount of force required to hold the spray container can be reduced by providing a rear support on the sprayer head. The rear support would allow the sprayer head to rest on the user’s hand eliminating the need to tightly grasp the container.

Figure 20: The rear support on this trigger spray bottle eliminates the requirement for tight grasping.



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Guideline: Avoid sharp edges.Source: GTRI

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The actuator must be squeezed or depressed multiple times to dispense the desired volume of contents.Detailed Description:Depending on the type of product, users may want to dispense only a small amount of the contents of a spray container (such as a nasal spray), or they may want to dispense a larger amount (such as when spraying a cleaning product in the bathtub). For some users with arthritis, this task is difficult because it requires the user to squeeze the trigger or depress the actuator multiple times to dispense the desired volume of contents. This can result in pain and fatigue in the hands.

There are several factors that affect the amount of product that is dispensed with each time the actuator is depressed. The viscosity and the density of the product, the size of the nozzle and the orifice, and the spraying mechanism all affect the amount of product that is dispensed. Additionally, some spray containers allow the user to adjust the droplet size and volume of contents dispensed by twisting the nozzle.

Potential Solutions:Increase the size of the orifice. Increasing the size of the orifice increases the flow rate. As a result, more contents are dispensed each time the actuator is depressed. However, increasing the orifice size and flow rate also produces larger droplets, so this solution may not be suitable for all applications.

Use a trigger sprayer rather than a fingertip sprayer mechanism. Trigger sprayers expel more liquid each time the actuator is depressed compared to fingertip sprayers. Additionally, trigger sprayers may be easier to use for some individuals with arthritis in their hands since individuals are typically able to apply more force when gripping and squeezing an item with their whole hand rather than pushing down with one or two fingers.

Allow users to select the volume of liquid expelled with an adjustable nozzle. An adjustable nozzle works by altering the flow rate and the size of the droplets that are expelled. To create a fine mist and reduce the amount of liquid that is expelled each time the actuator is depressed, the nozzle is tightened closer to the tube which then limits the flow of fluid and increases fluid pressure. To create a spray and increase the amount of liquid that is expelled each time the actuator is depressed, the nozzle is loosened to increase the area of the nozzle exit. This allows fluid to flow more freely and reduces fluid pressure.

Use a power sprayer instead of a manual sprayer. With a power sprayer, the actuator is depressed only once and held down for as long as is necessary to dispense the desired volume of contents, eliminating the requirement for repetitive actions. One potential issue with power sprayers, however, is that the batteries and spraying mechanism increase the weight of the container. Users with arthritis may experience difficulty managing a heavy spray container.

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Figure 21: A power sprayer minimizes the number of actions a user must perform.

Applicable Guideline: Guideline: Verify that the requirement for constant, uninterrupted actions is

minimized by investigating the required actions for each control.Source: Vanderheiden, 1997 [28]

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The actuator is too small.Detailed Description:The actuator of some spray containers, such as aerosol spray cans, are very small and must be depressed with only one finger. Individuals with arthritis may not be able to exert the amount of force required to depress the actuator and dispense the product using only one finger. Additionally, individuals with arthritis in their fingers are likely to experience significant pain when pressing down on the actuator, especially if it must be depressed for an extended period of time.

Potential Solution:Increase the size of the actuator. By increasing the size of the actuator, users can depress the actuator using more than one finger and are able to exert more force on the actuator. One easy way to implement this for aerosol spray cans is to create a plastic cap that attaches to the neck of the spray can and provides a button with a larger surface area for users to press and dispense the product.

Figure 22: A cap provides a larger surface area for users to press against when dispensing the product.



Guideline: Provide a sufficient area for users to apply force.Source: GTRI

Guideline: Avoid sharp edges.Source: GTRI

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Design GuidelinesThe design and evaluation of spray containers can be informed by guidelines that have been suggested by researchers. Note, however, that the number of published studies addressing human performance in using spray containers is limited, and the quality of existing research may be questionable if a small subject sample was used or if the experimental designs were flawed. Therefore, it is important to document the sources for the guidance offered in this report. Careful review of the sources may lead to a better understanding of how to interpret the guidelines presented here and of how to allocate future research resources. The spray container guidelines referenced in this report are shown in Table 8.

Table 8: Ease of use guidelines for spray container design.

Guideline Guideline Source(s) Discussion Applicable

Components

Ensure that the product is easy to grip and control. The shape of the product should be easy to hold so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.

Cushman & Rosenberg, 1991 [6]; Haigh, 1993 [15]

- Container body- Closure- Outer packaging- Spray head

connector- Actuator

Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.

Steinfeld & Mullick, 1990 [26]

By providing alternatives to a standard grip, users with arthritis can adopt a grip that does not create pressure points on inflamed joints.

- Container body- Closure- Outer packaging- Spray head

connector- Actuator

Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.

Steinfeld & Mullick, 1990 [26]

This includes products that must be grasped with one hand while opening the closure with the other hand. This guideline is especially important for heavy containers and for containers with a low coefficient of friction on the surface.

- Container body- Closure- Actuator

(trigger)

Provide a high friction grip surface on cylindrical containers. Tight grasping of the container is required to provide a counter-rotational force when removing a twist off closure. Provide a high friction surface on a cylindrical container to facilitate tight grasping.

GTRI Tight grasping of the container is required to provide a counter-rotational force when removing a continuous thread closure.

- Container body- Closure- Spray head

connector

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Components

Provide a non-cylindrical grip feature, such as grip indentions, or use a non-cylindrical container.

GTRI Non-cylindrical grip features enhance grip while removing a closure and while dispensing the contents of a spray container.

- Container body

Enhance readability and comprehension of labels, critical instructions, and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.

GTRI - Labeling

It is essential that a warning be as salient as possible to capture the attention of users. The salience of a visual warning can be enhanced using large, bold print, high contrast, color, borders, and pictorial symbols.

Wogalter, Conzola, & Smith-Jackson, 2002 [30]

- Labeling

A warning should contain a signal word to attract the attention of the user.


- Labeling

To increase effectiveness and salience, warnings should be presented as bullets in an outline format.


- Labeling

Provide at least one mode of operation that does not require fine motor control or simultaneous actions, and that is operable with limited reach and strength.

Section 508 1194.31(f) [12]

- Outer packaging- Closure- Sprayer head- Actuator

Do not require the use of tools. GTRI Tools may be used in an unsafe manner leading to injury.

- Outer packaging

Require a pinch force of no more than 3.0 pounds (13.3 N).

GTRI Preliminary data collected by GTRI suggests that pinch force requirements should not exceed 3.0 pounds for users with arthritis. Further research is necessary to validate this finding.


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Components

Ensure that the proper method of removing the outer safety seal is clearly evident, either through the design of the safety seal or because of instructions printed prominently on the packaging. For example, if the seal is removed by twisting the cap to break the seal, instructions like “Twist cap to break seal” should be provided. If the seal is removed by pulling a perforated strip, the strip should be clearly visible.

Vanderheiden, 1997 [28]

The steps required to open some containers may be intuitively obvious to most users and therefore may not require printed instructions.

- Outer packaging

If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.

GTRI - Outer packaging

Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the fingers.

Pirkl, 1995 [22] By offering redundant modes of operation, users have the option to avoid using joints in which pain and swelling are most severe.

- Container body- Outer packaging- Closure- Actuator

Minimize user actions. HFDS 2.6.8 [11] Packaging should be designed to minimize hand and eye movements, thus maximizing efficiency.

- Container body- Closure- Outer packaging- Labeling- Actuator

On seal tabs, provide a sufficiently large grasping point. A tab that is at least 0.47 inches (12 mm) wide by 0.79 inches (20 mm) long is recommended.

Department of Trade and Industry, UK, 2003 [10]

This study was based on a smooth tab. The study looked at only one tab width and two tab lengths (0.47 inches and 0.79 inches) and only used rectangular tabs. The test population included individuals with disabilities, but the sample was relatively small with a wide variety of disabilities.

- Outer packaging

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Components

Provide texture on the grasp point that facilitates gripping the tab. The grasp point should be textured with a series of bumps or raised strips that are perpendicular to the peel direction.

Department of Trade and Industry, UK, 2003 [10]

- Outer packaging

On seals that are intended to be grasped and peeled from the container, place the grasp point in a location selected for the application of optimum force.

GTRI - Outer packaging

Minimize rotational force required to remove the closure from the factory sealed position.

Berns, 1981 [3]; Langley, Janson, Wearn, and Yoxall, 2005 [18]; Voorbij and Steenbekkers, 2002 [29]

The research available on this topic is very limited. The amount of rotational force that a user can apply to a continuous thread closure depends on the diameter and height of the closure, the coefficient of friction of both the closure and container, the shape of the container, and the type of grasp users adopt.

- Closure- Sprayer head

Avoid sharp edges. GTRI The actuator on spray containers should be beveled and devoid of sharp edges. Knurls and serrations on continuous thread closures should also be rounded.

- Closure- Sprayer head- Actuator

Screw top caps should fit in the hand. Their removal should require no more than ¼ turn for each angular movement, and no more than two angular movements should be required.

Haigh, 1993 [15] The study referenced did not address replacing the closure.

- Closure- Sprayer head

Provide a sufficient area for users to apply force.

GTRI The force required to complete a task, such as depressing the actuator, can be applied more easily when the force is applied to a larger surface area. Additional research is required to quantify what constitutes a “sufficient” area for applying force.


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Components

Verify that the requirement for constant, uninterrupted actions is minimized by investigating the required actions for each control.

Vanderheiden, 1997 [28]

- Closure- Sprayer head- Actuator

Controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum.

Section 508 1194.23(k)(2) [12]

Section 508 sets a broad guideline for maximum linear force requirements for all user actions. The guideline may not be directly applicable to the tasks involved in using a spray container. Further research is needed to determine if the 5.0 pound recommendation should be modified for this application.

- Container body- Outer packaging- Closure- Sprayer head- Actuator

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