Heat Stress: Defining, Evaluating and Preventing. Glenn E. Lamson CIH OSHA Health Response Team 2012 OSHA Oil & Gas Safety Conference

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2 Heat Stress: Defining, Evaluating and Preventing Glenn E. Lamson CIH OSHA Health Response Team 2012 OSHA Oil & Gas Safety Conference

3 Defining Heat Stress The net heat load that a worker is exposed to from the combination of metabolic heat, environmental factors and clothing Heat Strain The body s overall physiological response from heat stress.

4 Defining Core Temperature Temperature of blood circulating around the hypothalamus, aka the body s thermostat Best way to measure heat stress 37 0 C or F Equilibrium Heat gain = heat loss

5 Defining Metabolic heat loss pathways Sweating (evaporative cooling) Blood flow (radiant cooling) Hormonal (regulation of salt & H 2 O balance) Anti-diuretic hormones reduce water and salt losses through the kidneys

6 Defining: Heat balance equation Δ S = (M-W) ± C ± R E Δ S is the change in the body s heat content (M-W) is metabolism minus the work being performed and is always positive C is convective heat being exchanged R is radiant heat being exchanged E is evaporative heat loss and is always negative

7 Defining: (M-W) Metabolism Energy necessary to keep the body functioning and accomplishing work Estimated by oxygen consumption ~ 5 kcal/liter of O 2 Metabolism is best derived from the table in the ACGIH s TLV booklet.

8 Defining ± C Convective heat loss or gain Heat transfer between skin and air Function of air velocity Skin temperature is 35 0 C so C will be positive when air temperature is over 35 0 C E Evaporative heat loss Perspiration evaporation causes body heat reduction Function of air motion humidity If humidity is 100% E=zero

9 Defining: ± R Radiant heat Heat form electromagnetic radiation when it strikes an object. From skin and surrounding surfaces DOES NOT heat the air it passes though Important in hot environments and easily controlled

10 Defining: Some rules of thumb ± C: When ambient temp rises above skin temp, heat loss by convection is eliminated. E: When humidity levels increase heat loss by evaporation is markedly reduced As EH&S practitioners we have the most control over metabolism and radiant heat.

11 Defining: Heat disorders Heat stroke Heat exhaustion Heat syncope Heat cramps Heat rash

12 Defining: Heat disorders Heat Stroke Heat stroke is the most serious heat-related disorder. It occurs when the body becomes unable to control its temperature The body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. When heat stroke occurs, the body temperature can rise to 106 degrees Fahrenheit or higher within 10 to 15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not given.

13 Defining: Heat disorders Heat Stroke A medical emergency - call 911! Symptoms Hot, dry skin, hyperthermia, brain disorders Treatment Move the victim to a cool area Cool body rapidly Treat for shock Transport to hospital

14 Defining: Heat disorders Heat exhaustion Heat exhaustion is the body's response to an excessive loss of the water and salt, usually through excessive sweating. Workers most prone to heat exhaustion are those that are elderly, have high blood pressure, and those working in a hot environment.

15 Defining: Heat disorders Heat exhaustion Symptoms Clammy moist skin usually with a raised body temperature Fatigue, weakness, nausea, headache, fainting Treatment Remove from heat Give fluids Fainting implies hospital visit

16 Defining: Heat disorders Heat syncope Fainting (syncope) episode or dizziness that usually occurs with prolonged standing or sudden rising from a sitting or lying position. Factors that may contribute to heat syncope include dehydration and lack of acclimatization.

17 Defining: Heat disorders Heat syncope Symptoms Light-headedness Dizziness Fainting Treatment Sit or lie down in a cool place at onset of symptoms Slowly drink water or a sports beverage

18 Defining: Heat disorders Heat cramps Muscle spasms caused by electrolyte loss Symptoms: Muscle pains or spasms usually in the abdomen, arms or legs Treatment: Stop activity and sit in a cool place Drink clear juice or a sports beverage Do NOT return to strenuous work for a few hours after cramps subside

19 Defining: Heat disorders Heat rash AKA Prickly heat a skin irritation from excessive sweating Symptoms: red cluster of pimples or small blisters Most likely on the neck and upper chest, groin, elbow crease and below breasts Treatment: Keep the affected area dry Dusting powders can increase comfort

20 Evaluating: Measures of heat stress Wet bulb globe temperature Traditional measure of heat stress, easy to measure and basis for ACGIH TLV Incorporates air temperature, radiant heat, air movement and humidity Indoors WBGT = 0.7t nwb +0.3t g Outdoors (and indoors when there is a radiant heat source) WBGT = 0.7t nwb +0.2t g +0.1t db

21 Evaluating: Wet bulb globe temperature Forget that formula this is all you need

22 Evaluating: Measures of metabolic rate Work category Metabolic rate Work examples Rest 115 Sitting Light 180 Moderate 300 Heavy 415 Very Heavy 520 Sitting, standing, light arm/hand work occasional walking Normal walking, moderate lifting Heavy material handling walking at a fast pace Pick and shovel work

23 Evaluating: Clothing effects Clothing alters convective and evaporative heat exchange Insulating effects estimated using clothing adjustment factors (CAFs)

24 Evaluating: Clothing Adjustment Factors CAFs are a function of clothing thickness Work Clothes (long sleeves and pants) = 0 Coveralls (w/ only underwear under) = 0 Double-layer woven clothing = 3 Polyolefin coveralls = 1 Limited-use vapor-barrier coveralls = 11 Can not be added and do not apply to completely encapsulating suits (level A)

25 Evaluating: Applying CAF s to WBGTs Once WBGT is calculated or measured you need to adjust the value to the worker s dress level Add the clothing adjustment factor to the WBGT value (all values in C) provides the Effective WBGT (WBGTeff)

26 Evaluating: Acclimatization Gradual physiological adaptation that improves ability to tolerate heat stress Acquired by time lost even faster Gained when working in heat 2 hours a day for 5 of the last 7 days to 10 of last 14 days Loss begins when work in heat is discontinued. Noticeable loss in 4 days, complete loss in 3-4 weeks. Situations to monitor New hires Returning vacationers

27 Evaluating: Tying all of that together How to us all those calculations.. ACGIH TLV WBGT eff Metabolic rate Action Limit Replaces unacclimatized TLV Work below action limit is presumed to be low stress for any healthy worker

28 Evaluating: Tying all of that together Lets take an example... Joe is a 38 year welder who has been working on a turnaround for 2 months Joe wears jeans, a long sleeve shirt under a pair of flame retardant coveralls WBGT is 27 and it has been hot for a month Calculation: WBGT eff = 27+3 or 30 Assuming that his work is moderate, using the TLV he should be further evaluated for susceptibility for heat strain.

29 Evaluating: Tying all of that together Lets take a further look at that example... Variables: W= between TLV & AL Metabolic work rate CAF TLV has a ~ 3 0 between W=300 and W=415 CAF for double-layer woven clothing is 3

30 Evaluating: One more thing

31 Evaluating: Measures of heat stress NOAA s Heat index A measure of how hot it feels when the amplifying effects of increased humidity is factored into the actual air temperature. Reported daily

32 Evaluating: Measures of heat stress Heat Index: Limitations Developed for shady, light wind conditions the heat index does not take into account site specific factors such as metabolic work rate, radiant heat, acclimatization or clothing. Exposure to full sunshine can increase the heat index values by up to 15 F.

33 Preventing: Safety & Health Plan Heat injury safety and health plans Essential after exceeding the TLV Should be written and spell out controls Anticipate Evaluate Control Engineering Administrative PPE

34 Preventing: Safety and Health Plan Goal: Protect all workers from heat strain Targets: workers over the AL and in PPE Symptoms triggering action Sustained HR >180 bbm age Core temp > C or C (unacclimatized) Recovery HR >120 bbm Sudden and severe fatigue, nausea, dizziness or lightheadedness

35 Preventing: Engineering Controls Ventilation: removing the heat or adding cooling Shielding: protecting workers from radiant heat waves Important in processing plants 15 times the radiant temperature minus skin temp SHADE!!!

36 Preventing: Administrative Controls Work-rest cycles Shade Proper hydration Acclimatization Worker monitoring

37 Preventing: Personal protective equipment Cool vests Vortex cooling suits

38 Glenn E Lamson CIH OSHA HRT lamson.glenn@dol.gov

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