Thermal StressITEC 471 Spring 2003 Jon Judge: Guest Lecturer

What is thermal stress?By the end of this unit, you will be able to: -define thermal stress -calculate WGBT (loaded/unloaded) -recognize control measures for thermal stress -assess risk/exposure for thermal stress -determine exposure limits for thermal stress

Thermal StressThermal stress is defined as the physical and physiological reactions of the worker to temperatures that fall outside of the workers normal comfort zone.

Comfort Zones-Accepted method of determining comfort zones is through the use of an ASHRAE chart. -ASHRAE American Society of Refrigeration, Heating, and Air-Conditioning Engineers. -ASHRAE standard 55-1981 outlines human comfort zones based on temperature and humidity.

Heat and Heat BalanceCooling

External Heat SourceH

Internal Heat Source (Muscular Activity)

Temperature Regulation is a balancing act

Measuring temperatureAccurate temperature measurement is crucial for determining thermal stress. WBGT (Wet Bulb Globe Temperature) is the accepted method for determining true temperatureAccounts for air currents, relative humidity, solar load

WBGT Heat Stress MonitorHeat Stress Monitor takes readings from, and calculates WGBT by:

-Dry Bulb Thermometer-Wet Bulb Thermometer -Globe Temperature

WBGT Formulae:For indoor or shaded environments:

WBGT = 0.7 x Tnwb + 0.3 x Tg

Tnwb = natural wet-bulb temperature Tg = globe temperature For direct sunlight exposure:

WBGT = 0.7 x Tnwb + 0.2 x Tg + 0.1 x TdbTdb = dry-bulb temperature

WGBT ExampleUsing the reading from the thermostat on the west wall, convert that temperature to WBGT using the following info:-WB = 64.1 F -GT = Temperature reading from thermostat

WBGT Example, contdStep 1 : Convert F temps to C-5/9 (temp F) 32 = temp C *5/9 (64F) 32 = 17.77C *5/9 (thermostat F) 32 = ?

WBGT example, contdWBGT = 0.7 x WB + 0.3 x GTWBGT = ? WBGT =

WBGT example, contdVerification of readings : Using WB temp and WBGT from monitor, calculate the corresponding GT, which should agree with the thermostatif its accurate.* GT = (WBGT 0.7(WB))/0.3 * convert temp to F - 9/5(Temp C) + 32 = Temp F

Using the readings from WBGTWBGT is used by Industrial Hygienists to determine the workload requirements/restrictions for work areas, using Heat Stress/Strain TLV.

TLVs

TLVs, contdNotice the ACGIH Heat Stress/Strain TLVs take into account the workload as well as the work/rest cycle.Also to note that the TLVs make a few assumptions regarding acclimatization, clothing, water and salt intake, as well as the ability of most workers to work continuously at 38C.

TLV workload definitions:Light: standing with light work at machine/bench using mostly arms; using table saw Moderate: walking about with moderate lifting or pushing; scrubbing in a standing position Heavy: shoveling dry sand; cutting with a hand saw Very Heavy: shoveling wet sand

TLV correction factorsThe following correction factors for the WBGT should be used:

WBGT and TLV Screeningwork demands:100% work; (breaks incl.) 75% work; 25% rest 50% work; 50% rest 25% work; 75% restAcclimatized

light29.5 27.5 30.5 29.0 31.5 30.0 32.5 31.0

moderate27.5 25.0 28.5 26.5 29.5 28.0 31.0 29.0

heavy26.0 22.5 27.5 24.5 28.5 26.5 30.0 28.0

very heavynot allowed not allowed 27.5 25.0 29.5 26.5

Unacclimatized

Acclimatization-The process whereby the body adapts to the temperature variations of the area. Acclimatization requires up to 3 weeks to be fully established and is noticeably decreased after 4 days (for TLV purposes: use 5 of last 7 days) Having lost 1.5% of your body weight due to dehydration eliminates any benefit of being acclimatized

Acclimatization, contdBody Changes due to Acclimatization:

Ability to get rid of excess heat improves sweating becomes more efficient (1500 mL/h vs. 700 mL/h non-acclimatized) Decreased loss of electrolytes (less salt in sweat) Blood flow to skin is reduced; more blood is available to muscles Heart rate more stable, heart stoke volume increases and blood volume increases Decreased stress response(s)

Screening Measurements:Heat Stress/Strain measurements (WBGT) should be taken prior to work being performed, to allow for measures to be taken to protect exposed individuals. Anticipated workload, work/rest cycle, clothing should be taken into account in determination. If work/rest cycle is not constant, time-weighted average should be used in determination.

Cooling the bodyThe bodys cooling system can be likened to the cooling system of a car.-Coolant (blood) is circulated through a pump (heart) and moves heat from the hot inner core to a radiator (skin surface).

Temperature RegulationThe hypothalamus is a small organelle within the brain which adjusts bodily functions through hormones which: -Increase heart rate -Begin the sweating mechanism -Increase blood flow to the skin surface

Changes in blood flow14 12 skin core muscles organs

blood flow (L/min)

10 8 6 4 2 0 cool hot

How does the body rid itself of excess heat?There are 4 means of heat removal from the body.Convection Radiation Evaporation Conduction

ConvectionConvection is the transfer of heat by movements of air masses.Air cooling

Hot air rising

Cool air descending

RadiationRadiation is the outward flow of energy from a source to the surrounding environment.

EvaporationEvaporation is the process of a liquid changing state into a gas. For our discussion, it is the process where large sweat droplets are reduced in size and become vapor suspended in air.Sweat vapor

Sweat droplet

ConductionConduction is the process where energy is transferred between objects through direct contact.Hot Cold

Heat loss, contdWhen the body is cool the majority of heat escapes from the body by convection (draft passing over the skin) and radiation (60% heat loss at cool temperatures; the reason why its important to cover your head in winter) BUT When under heat stress up to 80% of heat loss is by evaporation

Heat SourcesIt must be remembered that there are two sources of exposure to heat (external and internal)70-80% of muscle expended activity in the body is changed into heat (rather inefficient) called metabolic heat

What are the health effects of heat stress/strain?

Heat InjuriesHeat Rash (prickly heat):Cause: Heat buildup in the skin due to clogged pores and sweat ducts. Prolonged skin wetness from sweating. Symptoms: Area becomes reddened and may itch or hurt. Skin eruptions. First Aid: Practice good personal hygiene; keep the skin clean and the pores unclogged, allow skin to dry, wear loose clothing, see doctor if rash persists. Seriousness: Relatively minor.

Heat InjuriesRadiation Burns (Sunburn)Cause: UV radiation is absorbed by the skin. Symptoms: Water molecules within skin are disrupted, leading to drying-out of tissues. Extreme cases involve blisters, ruptures, and deep-tissue damage. First Aid: Covering of exposed skin. Use of protective creams (sunscreen). Bandaging of serious burns. Seriousness: Minor to relatively serious.

Heat Injuries, contdTransient Heat Fatigue:Cause: Loss of fluids reduces circulatory efficiency. Symptoms: General feeling of tiredness or fatigue. First Aid: Fluid replacement and rest. Seriousness: No long-term adverse effects.

Heat Injuries, contdHeat Syncope: Cause: the bodys circulation system allows blood to pool in the lower extremities causing insufficient blood, and oxygen in the brain. Symptoms: Syncope means fainting. First Aid: Lay victim in a cool location horizontally with feet elevated. If conscious, give fluids. Seriousness: Victim may take a day or two to recover. May subsequently be more sensitive to heat until reacclimated.

Heat Injuries, contdHeat Cramps: Cause: Loss of important electrolytes in the blood and muscle tissues due to excessive amounts of salts being lost in the victims sweat. Symptoms: Cramping of either voluntary (skeletal) muscles or involuntary (principally abdominal) muscles (or both). First Aid: Replenish electrolytes through drinking of fluids constituted for this purpose such as Gator-Aide. Rest in a cool environment. Seriousness: May debilitate the victim for several days. Full recovery is necessary before going back into heat stress conditions.

Heat Injuries, contdHeat Exhaustion:

Cause: Depressed condition of the circulatory system due for the most part to a lack of adequate fluid replacement (dehydration). Blood vessels dilate and blood flow is seriously reduced (clinical condition of shock has occurred). A victim may be able to take actions that will alleviate the condition, if the symptoms are recognized early enough. Symptoms: Nausea, dizziness, weakness, headache, blurred vision, profuse sweating, cold/wet (clammy) grayish skin, unconsciousness, coma and death.

Heat Injuries, contdHeat Exhaustion (continued):

First Aid: Place victim in a face down position in a cool location, administer fluids if the victim is conscious. If unconscious, seek medical care or transport to a medical emergency room.Seriousness: Shock is a serious medical condition regardless of the cause of its onset. Victims may require several days or even weeks to recover. Even longer periods may be necessary before the victim can resume working in heat stress conditions.

Heat Injuries, contdHeat Stroke:

Cause: The bodys temperature regulation mechanism, located in the hypothalamus, fails and sweating stops. Core body temperature rises dramatically and the victims condition becomes a serious medical emergency. The victim is unlikely to be able to reverse the condition without assistance or medical intervention.Symptoms: Chills, restlessness, irritability, euphoria, red face and skin, disorientation, hot/dry skin (not always), collapse, unconsciousness, convulsions and death.

Heat Injuries, contdHeat Stroke (continued):

First Aid: Immediate, aggressive cooling of the victims body using wet cloths, immersion into cool water or using alcohol wipes. Transport to emergency medical facility.Seriousness: Heat Stroke is a MEDICAL EMERGENCY. Without outside intervention, the victim will die. By the time the victim realizes s/he is in trouble, it is usually too late to employ effective self-intervention procedures that can reverse the thermo-regulatory failure and reduce core temperatures. Recovery times from heat stroke are generally the longest of any heat-related disorder.

Heat Injuries, contdIndirect Heat-Related Health Effects:Reduced Work Performance: tired, fatigued workers perform with reduced accuracy, efficiencyIncreased Accidents: tired, fatigued workers are more susceptible to accident and injury Reproductive Problems: heat has been shown to reduce both male and female fertility and can be a problem for the fetus Heart/Lung Strain: if you already have heart, lung, kidney or circulatory problems; heat stress is an added strain on your body which in severe situation may precipitate serious episodes of acute problems

Heat effects and peopleHeat affects people in different ways. People come in all different sizes, shapes, and tolerances for heat. Some people can work comfortably in high temperatures, while others will develop sickness from heat stress/strain

Heat effects, contdPredisposing Factors: very small body size poor nutrition overweight over 40 years old (the older the more sensitive) previous heat illness heart disease high blood pressure diabetes skin disease liver, kidney, and lung problems

Heat effects, contdPredisposing Factors, contd: physical activity poor physical condition fatigue excessive clothing dehydration being female being pregnant alcohol, caffeine, nicotine intake Sunbathing

Heat effects, contd - DrugsDrugs that interfere with bodys thermo-regulation: Heat production:thyroid hormone amphetamines TCAs LSD

Decrease thirst:Haldol

Decrease sweating:antihistamines anticholinergics phenothiazines Benztropine

Control methodsEngineering controls Administrative controls

Personal protective equipment

Control methods - Engineering-

-

Use machinery instead of people where applicable Take steps to cool building or worksite Use thermal barriers (mylar reflective surfaces) More?

Control methods - Administrative-Conduct training on Heat stress/strain -Work during coolest part of day -Co-worker observation -Implement work/rest schedule -More?

Control methods - PPE-Drinking adequate amounts of fluids -Protective clothing (light colors reflect heat) -Protective equipment (vests, fans) -More?

Control methods PPE, contdCooling vest

Personal SafeguardsHow Much Water is Enough? More than you want just to satisfy your thirst Sources of water are:1. Fluids - 1 cup or 8 oz = 240 mL every 20 min 2. Foods - fruit & veggies are 90% water

Why 10-15C? to maximize the amount you drink (not too cold, not luke warm)

Does it need to be delivered to the work station? depends on workplace logistics

Personal Safeguards, contdWhat to drink: Electrolyte drinks (e.g. Gatorade) are usually not needed for typical North American diet (can be used for first aid). Stay away from caffeinated, carbonated, diet drinks, and alcohol as they take water out of your body. Water is the best; juices and/or no caffeine sport drinks are also good (juices contain energy restoring glucose).

Personal Safeguards, contd% weight loss 1% 2% 3% 4% 5-6% 7+% fluid loss 0.75 L 1.5 L 2.25 L 3L 3.5-4 L 5+ L time* 1 hr 2-3 hrs 3-4 hrs 4-5 hrs 5-6 hrs 7+ hrs effect & symptoms(* timing may vary based on intensity of work and heat/humidity)

unnoticed (at 1.5% weight loss you are considered dehydrated) loss of endurance, start to feel thirsty, feel hot, uncomfortable loss of strength, loss of energy, moderate discomfort cramps, headaches, extreme discomfort heat exhaustion, nausea, faint heat stroke, collapse, unconsciousness

Personal Safeguards, contdFans:Purpose of a cooling fan is primarily to increase the rate of sweat evaporation but it also cools by convection if the air is cooler than the skinFan coolers may interfere with local exhaust ventilation for contaminant control, therefore be careful in where they are placed

Personal Safeguards, contdFans, contd: The lower the relative humidity the better the evaporation the more effective the cooling If the relative humidity is close to 100% the fan will no longer increase evaporation of sweat The closer the air temperature is to skin temperature (35-36C) the less effective the coolingif the air temperature exceeds skin temperature then the fan may even heat up the body (like a convection oven)!

Protective/Corrective measuresTake readings: Select a representative spot to place your thermometer(s) and/or hygrometer Designate someone to take readings on an hourly basis (on the hour) and record them

If activities are altered in response to the heat (slow down, more breaks, water distribution) record the details including the time and the degreeIf heat stress health conditions appear record time and describe symptoms and situation

Protective/Corrective measuresThings you can check:Look for typical heat strain symptoms; feeling overheated, fatigue, headache, nausea, weakness, dark concentrated urine, etc. Sweat that drips off your body no longer allows for cooling by evaporation; thus, unless theres another medical reason for it, this is a sign that your body is heating upCheck your pulse; heat stress is unlikely if your pulse rate is under 100 beats per minute after 1 minute rest. MAKE SURE YOURE DRINKING ENOUGH!!!

Thermal Stress Cold Stress

Cold StressJust as high temperatures have far-reaching effects on the body, cold temperatures present their own challenges to the thermal regulation of the human body.Lets examine what the effects of cold temperatures are, what health effects cold temperatures present, and methods for treatment of cold-related injuries.

Normal vs. Hypothermic environment

Hypothermic environmentAs we see, the four causes of heat loss in a hypothermic environment are convection, radiation, evaporation, and conduction.

The large difference is that in hypothermic environments, you are trying to retain heat, instead of releasing it to the environment.

Bodys cold responseDetermining the risk of cold-injuries is done using the following formula: Heat Retention + Heat Production > Cold Factors or Heat Retention + Heat Production < Cold Factors

Cold Response, contd-

Heat Retention:-

-

Size/shape (Eskimo vs. Masai) Insulation (Clothing type/# of layers) Fat (Used as insulation) Shell (Blood in core of body)

These are positive factors. Increase of any or all of these factors decreases risk of injury.

Cold Response, contd-

Heat Production-

-

Activity level Shivering response * Limited by:-

-

Fitness level Nutrition Fluid intake

Cold Response, contd

Cold Response, contd-

Cold Factors:-

-

Temperature Humidity Wind

The total of these represents the challenge to the thermo-regulation of the human body. If Retention + Production < Cold Factors, Hypothermic condition could develop.

Hypothermiaa decrease in the core body temperature to a level at which normal muscular and neurological functions are impaired Medicine for Mountaineers

Hypothermia is possible at any temperature under 98.6 degrees, if the right conditions exist (lack of insulation, increased heat loss, etc.)

Hypothermia - signsUmbles Stumbles, Mumbles, Fumbles, and GrumblesShows decreased physical and mental capacity.

Hypothermia - mildMild Hypothermia: - core temperature 98.6 96 F - non-voluntary shivering -complex motor functions impossible -vasoconstriction to periphery

Hypothermia - moderateModerate Hypothermia: - core temperature 95 93 F - loss of fine motor coordination - slurred speech - violent shivering - paradoxical undressing - apathetic attitude

Hypothermia - severeSevere Hypothermia: - core temperature 92 86 F or below - shivering in waves (violent then pause) - person curled in fetal position to conserve heat - muscle rigidity develops - pale skin/dilated pupils - reduced pulse

Hypothermia severe, contd-at 90 degrees F, the person goes into hibernation, slowing heart rate and respiration, shunting blood to peripheral tissues. -at 86 degrees F or below, the person looks dead, but is still alivebarely. Severe Hypothermia is LIFE THREATENING!

Cold InjuriesAlthough hypothermia is well known, there are other cold injuries. -Frostnip -Frostbite -Immersion foot (trench foot)

FrostnipFrostnip is the freezing of upper layers of the skin. Characterized by: - white, waxy skin. - general numbness Frostnip is generally reversible and does no major tissue damage.

Frostnip - treatmentGently warm area by blowing warm air on it or by placing it near a warm body part. DO NOT rub the area! Rubbing can rupture frozen cells, causing extensive damage.

Frostnip is a warning sign of possible frostbite*

FrostbiteFrostbite is a freezing of the surface and deep layers of tissue. Characterized by: - white, and feels woody - numbness, possible anesthesia - deep frostbite can affect bone and muscle - purple/black color is from ruptured blood vessels

Frostbite a view

Frostbite - treatmentImmerse affected area in 105 110 degree F water until thawing is complete. - part will be extremely painful Wrap affected part in sterile gauze Affected part should not be used for anything - keep part from refreezing

Chart

Immersion Foot trench footImmersion foot is caused by prolonged exposure of the feet to wet, cool conditions. Characterized by: - yellowish, smelly feet - possibly numb - sloughing of skin tissue/itching *Immersion foot may cause permanent damage to foot tissues, leaving person susceptible to cold injuries in future.

Immersion Foot a view

Immersion Foot - treatment-

Careful washing and drying of feet. Keep feet dry as much as possible. Keep off feet as much as possible until healed.

Final Thoughts or Questions?

ReferencesCurtis, Rick. Outdoor Action Program. Princeton University. 1995 Occupational Safety and Health Administration 3154 Occupational Safety and Health Administration 3156 Occupational Health Clinics for Ontario Workers. Heat Stress Training. 2001 Plog, Barbara A. et al. Fundamentals of Industrial Hygiene. 1996 USAF. Heat Stress Fact Sheet. 1998 www.firstworldwar.com/atoz/trenchfoot.html