5_50480_larsonhazadouslocationratings.pdf

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Hazardous LocationRatings—BreakingDown the Facts

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Hazardous Location Ratings—Breaking Down the Facts 1

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1

Hazardous Location Ratings—Breaking Down the Facts

Sometimes electrical equipment must be installed in areas wherecombustible vapors and gases are used or may be present. Theseare commonly referred to as “hazardous locations”, and are defined by the National Electrical Code (NEC) in the US. When equipmentmust be installed in these locations, there are strict requirements forthe construction of the installation, including materials and designrequirements. Electrical equipment intended for use in a factory orrefinery is designed either to contain any explosion within the device,or is designed not to produce sparks with sufficient energy to trigger

an explosion. We will break down the ratings so you can decide whatequipment will be safe in your environment.

An area such a home or office is classified as a Non Hazardous orSafe Area. The only release of an explosive would generally comefrom an aerosol can. A common flammable liquid would be paintthinner or brush cleaner. These are a very low risk of causing anexplosion, and are more likely to cause a fire. Non Hazardous areasin a factory or chemical plant are those areas where it’s absolutelycertain that the gases or vapors are “diluted” to a level below itsflammability limit.

Hazardous locations are broken into 3 “Classes”. Each class definesthe type of substances that may be ignitable or explosive in the atmo-sphere. Class I areas are those locations that have gases, vapors orliquids present. This includes acetylene, hydrogen, fuels and sol-vents. Class II areas have dust hazards. Class III covers fibers andshavings, types of combustibles that could be found in textile manu-facturing or woodworking environments.

Each of the three classes listed above are further divided into 2 divi-sions. This is determined by the likelihood the hazardous material being present in flammable concentrations. Division 1 is which ignit-able concentrations of the hazards exists under normal operation

conditions and/or where hazard is caused by frequent maintenanceor repair work or frequent equipment failure. Division 2 is whereignitable hazards are handled, processed or used, but which are nor-mally in closed containers or closed systems from which they canonly escape through accidental rupture or breakdown of such con-tainers or systems. In other words, in a Division 2 environment, thehazards are “occasionally present.”



ponsored by

Since 1973 Larson Electronicshas manufactured industrial

ighting and power distribu-

ion products. Our products

are used by refineries, military

bases, paint spray booths, oil-

field operations, shipyards and

manufacturing facilities around

he world. Larson Electronics

continues to develop custom

solutions while maintaining an

extensive inventory of estab-ished products for immedi-

ate shipping. Learn more by


nformation and products at

www.larsonelectronics.com.

Class I and Class II Divisions are further subdivided into Groups A,B, C, and D. Group A is considered the most hazardous, with GroupD being the least hazardous for gases and vapors. The explosivecharacteristics of the air mixtures of gases, vapors, or dusts vary withthe specific material involved. The Groups define substances by

rating their flammable nature in relation to other known substances.Each material has been placed in a Group based on its ignition tem-perature and explosion pressure. Group A covers atmospheres con-taining acetylene. Group B is areas containing hydrogen or gases.Group C is defined as an atmosphere containing ethyl-ether vaporsor ethylene. Finally, Group D defines areas containing gasoline,hexane, benzene, butane, propane, alcohol, acetone, lacquer solventvapors, or natural gas (methane).

So now that we have listed the Classes, Divisions and Groups, wecan explain the areas in a little more detail. A Class I, Division 1 areacan be applied to 3 different situations:

1. When the atmosphere of an area or location is expected tocontain explosive mixtures of gases, vapors, or liquids duringnormal working operations. (This is the most common Class I,Div. 1)

2. An area where ignitable concentrations frequently exist because of repair or maintenance operations.

3. The release of ignitable concentrations of gases or vapors dueto equipment breakdown, while at the same time causing elec-trical equipment failure.

Next, one of the following scenarios must exist in order for an area to be considered a Class I, Division 2 location.

1. Areas where flammable liquids and gases are handled, but notexpected to be in explosive concentrations. However, therecould be a level of concentration should an accidental ruptureor other unexpected incident.

2. An area where ignitable gases or vapors are normally pre-vented from accumulating by positive mechanical ventilationyet could exist in ignitable quantities if there was a failure inthe ventilation.

3. Areas next to a Class I, Division 1 location where it is possiblefor ignitable concentrations of gas/vapors to come into thisarea because there isn’t proper ventilation.

10 Tips to Implementing a Lockout/Tagout Program 2



Sponsored by

Since 1973 Larson Electronhas manufactured industria

lighting and power distribu

tion products. Our product

are used by refineries, milit

bases, paint spray booths,

field operations, shipyards

manufacturing facilities aro

the world. Larson Electroni

continues to develop custo

solutions while maintaining

extensive inventory of estalished products for immedi

ate shipping. Learn more b


information and products a

www.larsonelectronics.co

10 Tips to Implementing a Lockout/Tagout Program 3

If the following conditions exist, an area will be defined as a Class II,Division 1 location:

1. Where combustible dust is present in the air under normaloperating conditions in such a quantity as to produce explosiveor ignitable mixtures. This could be on a continuous, intermit-

tent, or periodic basis.

2. Where an ignitable and/or explosive mixture could be pro-duced if a mechanical failure or abnormal machinery operationoccurs.

3. Where electrically conductive dusts in hazardous concentra-tions are present.

A Class II, Division 2 locations exist due to one of the followingconditions:

1. Combustible dust is present but not usually in the air in con-

centrations high enough to be explosive or ignitable.

2. If the dust became suspended in the air due to an equipmentmalfunction and when the dust accumulations may becomeignitable by abnormal operation or failure of electronicequipment.

Class III ratings are the least stringent in the system.

1. Class III, Division 1: This defined as a location or area whereeasily ignitable fibers or items that produce ignitable flyings arehandled, manufactured or used in some kind of a process.

2. Class III, Division 2: A location or area where easily ignitablefibers are stored or handled.

The NECs ratings are very specific and detailed. Yet, not followingthese guidelines could be costly, or even deadly. Researching yourequipment, application, location, hazards that are present is essentialto providing a safer environment for all involved.

5_50480_larsonhazadouslocationratings.pdf

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