Heat and Cold Stress

1. Why Heat and Cold Stress Matter on the ASP Exam

Thermal stress is one of the most heavily tested physical agents in the Industrial Hygiene and Occupational Health domain of the BCSP Associate Safety Professional (ASP) exam. There are three reasons it gets so much attention:

• It kills workers every year. Heat is the leading weather-related cause of death in the United States, and the Bureau of Labor Statistics consistently records dozens of occupational heat fatalities annually, with many more non-fatal cases. Cold exposure adds hypothermia and frostbite injuries, especially in construction, utilities, agriculture, oil and gas, and cold-storage work.
• It is a regulatory and professional standard-of-care issue. OSHA has historically enforced heat hazards under the General Duty Clause, Section 5(a)(1), using the NIOSH Criteria Document and the ACGIH TLVs as evidence of recognized hazards and feasible controls. OSHA also launched a National Emphasis Program on heat and published a proposed Heat Injury and Illness Prevention rule. Several states (California, Washington, Oregon, Minnesota, Colorado, Maryland) have their own enforceable heat standards.
• It is highly quantifiable. The exam loves topics that combine physiology, measurement, calculation, exposure limits, and the hierarchy of controls. Thermal stress offers all of these: WBGT formulas, work/rest regimens, acclimatization schedules, physiological monitoring limits, and clothing adjustment factors.

If you understand how the body exchanges heat with its environment, you can reason through almost any question, even one you have never seen before.

2. What Heat Stress Is: The Core Concepts

Heat stress is the total heat load placed on the body from the combination of metabolic heat generated by work, environmental heat (air temperature, humidity, radiant heat, air movement), and the clothing worn. Heat strain is the body's physiological response to that load (increased core temperature, heart rate, and sweating). The goal of a heat stress program is to keep heat strain within safe limits.

The Heat Balance Equation

The human body must maintain a core temperature near 37°C (98.6°F). Heat exchange is summarized as:

S = M ± C ± R ± K − E

Where:
• S = heat storage in the body (we want S to be approximately zero)
• M = metabolic heat production (always positive; increases with work intensity)
• C = convective heat exchange with the air (body gains heat if air temperature is above skin temperature, roughly 35°C/95°F; loses heat if below)
• R = radiant heat exchange with surrounding surfaces (furnaces, sun, hot machinery, or cold walls)
• K = conductive heat exchange through direct contact (usually small unless touching hot or cold surfaces)
• E = evaporative heat loss from sweating (always a loss; the body's primary cooling mechanism in hot environments; limited by humidity and vapor-impermeable clothing)

Exam insight: When air temperature exceeds skin temperature, convection becomes a heat gain, leaving evaporation as the only avenue of cooling. When humidity is high, evaporation is impaired. This is why hot and humid conditions, or encapsulating suits, are so dangerous.

Heat-Related Illnesses (Least to Most Severe)

• Heat rash (prickly heat / miliaria): Blocked sweat ducts produce red, itchy bumps in areas where clothing is tight or skin stays wet. Treatment: keep skin clean and dry, rest in cool area.
• Heat cramps: Painful muscle spasms (abdomen, legs, arms) caused by electrolyte loss through sweating, often when workers drink water but do not replace salts. Treatment: rest, electrolyte-containing fluids.
• Heat syncope: Fainting or dizziness, typically from prolonged standing or sudden rising, due to blood pooling in dilated vessels of the legs. Common in unacclimatized workers. Treatment: sit or lie down in a cool place, hydrate.
• Heat exhaustion: Heavy sweating, weakness, dizziness, headache, nausea, cool and clammy or pale skin, rapid weak pulse, core temperature usually under 40°C (104°F). Mental status is generally normal or only mildly impaired. Treatment: move to cool area, loosen clothing, cool with water and fans, give fluids if alert, monitor closely. Can progress to heat stroke.
• Heat stroke: A life-threatening medical emergency. Core temperature at or above 40°C (104°F), altered mental status (confusion, slurred speech, seizures, loss of consciousness). In classic heat stroke the skin is often hot, red, and dry because sweating has failed; in exertional heat stroke common in workers, the person may still be sweating. Treatment: call 911, begin immediate aggressive cooling (cold water immersion is most effective, or soak with cold water and fan, ice packs to neck, armpits, groin). Do not give fluids by mouth if confused or unconscious. Cool first, transport second when possible.
• Rhabdomyolysis: Breakdown of muscle tissue from heat and exertion releasing proteins into the blood, causing kidney damage. Signs: muscle pain, weakness, dark cola-colored urine. Requires medical evaluation.

Exam insight: The single most important discriminator between heat exhaustion and heat stroke is central nervous system dysfunction. If the question describes confusion, bizarre behavior, or unconsciousness, the answer is heat stroke, regardless of whether the skin is wet or dry.

Risk Factors

Lack of acclimatization, high workload, heavy or impermeable clothing, dehydration, poor physical fitness, obesity, age, prior heat illness, alcohol use, certain medications (diuretics, antihistamines, beta blockers, some psychiatric medications), illness or fever, and lack of sleep. New workers and workers returning from more than a week away are at especially high risk; a large share of heat fatalities occur in the first few days on the job.

3. How Heat Stress Is Measured and Evaluated

Wet Bulb Globe Temperature (WBGT)

WBGT is the preferred index for occupational heat stress because it integrates the four environmental factors: air temperature, humidity, radiant heat, and air movement. Three instruments are involved:
• Natural wet bulb temperature (T_nwb): a thermometer with a wetted wick exposed to natural air movement; reflects the cooling effect of evaporation (humidity and wind).
• Globe temperature (T_g): a thermometer inside a 6-inch black copper sphere; reflects radiant heat plus air temperature and air movement.
• Dry bulb temperature (T_db): ordinary shielded air temperature.

Indoors or outdoors without solar load:
WBGT = 0.7 T_nwb + 0.3 T_g

Outdoors with solar load (direct sunlight):
WBGT = 0.7 T_nwb + 0.2 T_g + 0.1 T_db

Notice that the natural wet bulb carries 70 percent of the weight in both formulas, emphasizing that humidity (which limits evaporative cooling) is the dominant factor.

Worked example: Outdoor work in the sun with T_nwb = 26°C, T_g = 40°C, T_db = 33°C.
WBGT = 0.7(26) + 0.2(40) + 0.1(33) = 18.2 + 8.0 + 3.3 = 29.5°C.

When exposure varies during the shift, a time-weighted average WBGT is calculated over the hottest continuous 60-minute period (or 120 minutes for intermittent heavy work in some guidance): WBGT_avg = (WBGT₁t₁ + WBGT₂t₂ + ...) / (t₁ + t₂ + ...).

Heat Index

The National Weather Service Heat Index combines air temperature and relative humidity to give an apparent temperature. It is measured in the shade and does not account for radiant load, wind, workload, or clothing, so it is a screening tool (used in the OSHA-NIOSH Heat Safety Tool app) rather than the preferred occupational exposure metric. OSHA has used Heat Index categories (roughly: caution below 91°F, extreme caution 91 to 103°F, danger 103 to 115°F, extreme danger above 115°F) for planning. Exam insight: If a question asks for the most comprehensive index that accounts for radiant heat and air movement, the answer is WBGT, not Heat Index.

ACGIH TLV and Action Limit for Heat Stress

ACGIH publishes screening criteria as WBGT values that depend on metabolic work rate and the work/rest allocation. The Action Limit (AL) applies to unacclimatized workers; the TLV applies to acclimatized workers. The TLV is intended to keep core body temperature from exceeding 38°C (100.4°F) in nearly all healthy workers.

Work categories (approximate metabolic rates):
• Rest: about 115 W
• Light: about 180 W (sitting with light hand work, standing with occasional walking)
• Moderate: about 300 W (sustained moderate arm work, moderate lifting, normal walking)
• Heavy: about 415 W (intense arm and trunk work, shoveling, pushing heavy loads)
• Very heavy: about 520 W (very intense activity at near-maximum pace)

Representative TLV screening values for acclimatized workers (WBGT in °C):
• 75 to 100 percent work: Light 31.0, Moderate 28.0, Heavy 26.0 (very heavy not recommended)
• 50 to 75 percent work: Light 31.0, Moderate 29.0, Heavy 27.5, Very heavy 26.0
• 25 to 50 percent work: Light 32.0, Moderate 30.0, Heavy 29.0, Very heavy 28.0
• 0 to 25 percent work: Light 32.5, Moderate 31.5, Heavy 30.5, Very heavy 30.0

Action Limit values for unacclimatized workers run roughly 2.5 to 3°C lower (for example, Light continuous work AL is 28.0°C versus TLV 31.0°C). The pattern to remember: as work gets heavier, the allowable WBGT drops; as rest time increases, the allowable WBGT rises.

Clothing Adjustment Factors (CAF)

Because the TLV assumes a worker in light summer work clothing, ACGIH adds a correction to the measured WBGT for heavier or less permeable clothing:
• Work clothes (long sleeve shirt and pants): 0°C
• Cloth (woven) coveralls: 0°C
• Double-layer woven clothing: +3°C
• SMS polypropylene coveralls: +0.5°C
• Polyolefin (e.g., Tyvek-type) coveralls: +1°C
• Limited-use vapor-barrier coveralls: +11°C

Example: Measured WBGT is 26°C and the worker wears vapor-barrier coveralls. Effective WBGT = 26 + 11 = 37°C, which exceeds every TLV category. Encapsulating suits essentially eliminate evaporative cooling and require physiological monitoring rather than reliance on WBGT alone.

NIOSH Recommended Exposure Limits

NIOSH (Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments, 2016) publishes a Recommended Alert Limit (RAL) for unacclimatized workers and a Recommended Exposure Limit (REL) for acclimatized workers, as curves of WBGT versus metabolic rate. The REL/RAL concept parallels the ACGIH TLV/AL concept, and both aim to keep core temperature at or below 38°C.

Physiological Monitoring

When WBGT screening limits are exceeded, when clothing adjustments are large, or when work is in encapsulating PPE, direct monitoring of workers is used. Commonly cited limits:
• Sustained heart rate over several minutes should not exceed 180 minus age (beats per minute).
• Recovery heart rate one minute after a peak effort should be below about 120 bpm (older guidance: recovery heart rate at one minute above 110 bpm, or a drop of less than 10 bpm between minutes one and three, indicates excessive strain).
• Core body temperature should not exceed 38°C (100.4°F) for unacclimatized or medically unscreened workers, or 38.5°C (101.3°F) for acclimatized workers under medical supervision.
• Body weight loss over a shift should not exceed about 1.5 percent, indicating adequate hydration.
• Any symptoms of heat strain (sudden fatigue, nausea, dizziness, confusion) require removal from exposure regardless of numbers.

4. How Heat Stress Is Controlled

Apply the hierarchy of controls.

Engineering controls (preferred):
• General and local exhaust ventilation; air conditioning of control rooms and break areas
• Spot cooling and fans (fans help only when air temperature is below about 35°C/95°F and humidity is not extreme; above that, moving hot air increases convective gain)
• Reflective shielding or insulation of radiant sources (furnaces, ovens, boilers, hot pipes); shade structures outdoors
• Reducing humidity (dehumidification, eliminating steam leaks, covering open hot water tanks)
• Mechanization to reduce metabolic workload (hoists, powered equipment)

Administrative controls:
• Acclimatization: Full acclimatization takes about 7 to 14 days. NIOSH recommends new workers start at no more than 20 percent of the usual exposure on day one and increase by no more than 20 percent each day. Workers with previous experience returning after absence start at 50 percent on day one, then 60, 80, and 100 percent. Acclimatization begins to be lost after about a week away and is largely gone after 3 to 4 weeks.
• Work/rest schedules based on WBGT and workload; rest in cool, shaded areas
• Hydration: encourage drinking about one cup (8 oz, roughly 240 mL) every 15 to 20 minutes, not exceeding about 48 oz (1.4 L) per hour; water should be cool (10 to 15°C / 50 to 60°F) and readily available; for shifts over 2 hours with heavy sweating, electrolyte drinks or snacks are appropriate; avoid alcohol, excess caffeine, and energy drinks
• Scheduling hot jobs to cooler parts of the day or year; rotating workers
• Buddy system and supervisor observation to catch early symptoms
• Training on signs, symptoms, first aid, and the importance of reporting
• Medical surveillance and screening for predisposing conditions
• Written heat illness prevention plan and emergency response procedures

Personal protective equipment (last line):
• Ice-vests, phase-change cooling vests, water-circulating garments, air-cooled suits (supplied-air vortex coolers)
• Reflective aprons or suits for high radiant heat
• Light-colored, loose, breathable clothing; wide-brimmed hats outdoors

5. What Cold Stress Is: The Core Concepts

Cold stress occurs when the body loses heat faster than it can produce it, driving skin temperature and eventually core temperature downward. The same heat balance equation applies, but now the problem is excessive heat loss through convection (wind), conduction (contact with cold surfaces or water), radiation, and evaporation (wet clothing). Water conducts heat away roughly 25 times faster than air, so wetness is the single greatest aggravating factor, followed by wind.

Risk factors: wet or inadequate clothing, wind, physical exhaustion, dehydration, poor nutrition, alcohol (dilates blood vessels and impairs judgment), nicotine (constricts peripheral vessels, increasing frostbite risk), certain medications, predisposing conditions (diabetes, hypothyroidism, cardiovascular disease, Raynaud phenomenon), older age, and low body fat.

Cold-Related Injuries and Illnesses

• Chilblains (pernio): Repeated exposure of skin to cold (above freezing, about 1 to 16°C) causes inflammation of small blood vessels: redness, itching, swelling, blistering, typically on cheeks, ears, fingers, toes. Permanent damage to capillaries can cause recurrence.
• Trench foot (immersion foot): Prolonged exposure to wet, cold (not necessarily freezing) conditions, even at 60°F if feet are constantly wet. Reddening, numbness, swelling, blisters, tissue death in severe cases. Treatment: remove wet footwear, dry and warm feet, do not walk on affected feet, seek medical care.
• Frostnip: Superficial freezing of the skin surface; pale skin and numbness with no permanent damage if rewarmed promptly.
• Frostbite: Actual freezing of skin and underlying tissue, most often fingers, toes, nose, ears, cheeks. Signs: reduced blood flow, numbness, tingling, waxy or white/grayish-yellow skin, firm or hard tissue, blisters after rewarming. Treatment: move to warm area, remove wet clothing and constricting items, do not rub or massage the area, do not walk on frostbitten feet, do not use direct heat (stove, fire, heating pad), do not rewarm if there is a chance of refreezing, rewarm in warm (not hot) water about 37 to 39°C (99 to 102°F) or with body heat, seek medical attention.
• Hypothermia: Core body temperature below 35°C (95°F). Stages:
  – Mild (about 32 to 35°C / 90 to 95°F): intense shivering, loss of fine motor coordination, fatigue, confusion begins.
  – Moderate (about 28 to 32°C / 82 to 90°F): shivering stops, slurred speech, poor coordination, drowsiness, irrational behavior (paradoxical undressing), dilated pupils, slow pulse and breathing.
  – Severe (below about 28°C / 82°F): unconsciousness, very weak or absent pulse, cardiac arrhythmias, cardiac arrest.
Treatment: call for medical help, move to warm shelter, remove wet clothing, insulate the whole body including the head, warm the core first (chest, neck, groin) with blankets, warm packs, or skin-to-skin contact, give warm sweet non-alcoholic drinks only if fully alert, handle the victim gently (rough handling can trigger ventricular fibrillation), and do not assume death until the person has been rewarmed and evaluated (no one is dead until warm and dead). Give CPR if no pulse and no breathing.

Exam insight: Cessation of shivering is a sign of worsening, not improvement. A hypothermic worker who stops shivering and becomes confused has progressed to moderate hypothermia.

6. How Cold Stress Is Measured and Evaluated

Wind Chill Temperature

The Wind Chill Temperature (WCT) index combines air temperature and wind speed to express the equivalent cooling effect on exposed skin. Wind does not lower the actual air temperature but strips away the insulating layer of warm air next to the body, greatly increasing convective heat loss. The National Weather Service wind chill chart also gives frostbite times (for example, exposed skin can freeze in 30 minutes or less at a wind chill around −18°F, and in 10 minutes or less around −32°F). Note that wind chill applies to exposed skin and does not account for workload, clothing, or wetness.

ACGIH TLV for Cold Stress

The ACGIH cold stress TLV is designed to prevent core temperature from dropping below 36°C (96.8°F) and to prevent cold injury to extremities. Key provisions commonly tested:
• Workers should be protected from exposure to cold so that deep body temperature does not fall below 36°C (96.8°F); a single occasional drop to 35°C is tolerated under some conditions.
• Hand protection for fine work: When fine manual dexterity is required for more than 10 to 20 minutes at air temperatures below 16°C (60°F), provisions should be made to keep hands warm (warm air jets, radiant heaters, contact warm plates).
• Gloves: Below 4°C (40°F) for sedentary work, −7°C (20°F) for light work, and −17°C (0°F) for moderate work without fine dexterity, gloves should be used.
• Metal handles and bars: Below −1°C (30°F), metal handles of tools and control bars should be covered with thermal insulating material; bare skin should not contact cold metal.
• Heated warming shelters: Required for continuous work at or below −7°C (20°F) equivalent chill temperature; workers encouraged to use them at regular intervals.
• Work/warm-up schedule: A table for a four-hour shift specifies maximum work period and number of breaks as a function of air temperature and wind speed. For example, at −26 to −28°C (−15 to −19°F) with no noticeable wind, maximum work period is 75 minutes with 2 breaks; at the same temperature with 10 mph wind, 55 minutes with 3 breaks; at 20 mph, 30 minutes with 5 breaks; as conditions worsen, non-emergency work should cease. Below roughly −32°C (−25°F) with significant wind, non-emergency work generally stops.
• Workers in wet clothing should change immediately; outer layers should be wind- and water-resistant if the work environment is wet or windy.
• Eye protection for snow or ice-covered terrain to prevent snow blindness and glare, and to protect from blowing ice crystals at high wind speeds.
• New workers should not be required to work full-time in cold until they are accustomed (cold acclimatization is much less effective than heat acclimatization, but work tolerance does improve).
• Workers with conditions that reduce cold tolerance should be medically evaluated and may be excluded from work below −1°C (30°F).

7. How Cold Stress Is Controlled

Engineering controls: heated enclosures and cabs, radiant heaters, wind barriers and screens, insulated or heated hand tools and handles, warm air jets for hand work, dehumidification and drainage to reduce wet conditions, covering metal surfaces that may be touched.

Administrative controls: scheduling work during warmer parts of the day, work/warm-up schedules per ACGIH, warming shelters with warm fluids and dry clothing available, pacing work to avoid heavy sweating (which wets clothing), buddy system, monitoring weather and wind chill, training on signs and symptoms, allowing workers to set their own pace and take extra breaks, providing warm sweet drinks and adequate calories (avoid alcohol and limit caffeine), medical screening.

Personal protective equipment and clothing: the layering principle: an inner wicking layer (polypropylene or wool, not cotton, which holds moisture), a middle insulating layer (wool, fleece, down), and an outer wind- and water-resistant shell. Insulated, waterproof boots with removable liners; wool socks; a hat (significant heat loss from the uncovered head); mittens are warmer than gloves because fingers share heat; face protection (balaclava) in high wind; eye protection. Clothing should be loose enough to allow air trapping and circulation, and extra dry clothing should be available for changing when wet. Clothing insulation is expressed in clo units (1 clo is approximately a business suit; about 0.155 m²·K/W).

8. Exam Tips: Answering Questions on Heat and Cold Stress

Tip 1: Memorize the two WBGT formulas and know when each applies. Indoor or no solar load: 0.7 T_nwb + 0.3 T_g. Outdoor with solar load: 0.7 T_nwb + 0.2 T_g + 0.1 T_db. Check that the coefficients sum to 1.0. A classic trap is a question that gives all three temperatures for an indoor scenario; ignore the dry bulb and use the two-term formula. Practice the arithmetic so that unit mistakes do not cost you points.

Tip 2: Know what each thermometer measures. Natural wet bulb captures humidity and air movement (evaporative cooling potential). Globe temperature captures radiant heat. Dry bulb is plain air temperature. If a question asks which single environmental factor the WBGT weights most heavily, the answer is the natural wet bulb (humidity), at 70 percent.

Tip 3: Heat exhaustion versus heat stroke hinges on mental status. Confusion, disorientation, seizure, or unconsciousness equals heat stroke and a 911 call plus immediate aggressive cooling. Do not be fooled by a worker who is still sweating; exertional heat stroke victims often are. Heat exhaustion victims have normal or near-normal mentation, cool clammy skin, and respond to rest, cooling, and fluids.

Tip 4: Know the first-aid do-nots. Heat stroke: do not give oral fluids to a confused or unconscious person; do not delay cooling while waiting for an ambulance. Frostbite: do not rub, do not apply direct dry heat, do not walk on frostbitten feet, do not thaw if refreezing is possible. Hypothermia: do not give alcohol, do not handle roughly, do not rewarm extremities before the core, do not pronounce death before rewarming.

Tip 5: Remember the direction of the TLV table. Heavier work = lower allowable WBGT. More rest = higher allowable WBGT. Unacclimatized (Action Limit) values are lower than acclimatized (TLV) values. If a question gives a WBGT and work category and asks whether the TLV is exceeded, compare against the correct cell and remember to add the clothing adjustment factor first.

Tip 6: Know the clothing adjustment factors, especially the big one. Vapor-barrier coveralls add 11°C to WBGT. Double-layer woven adds 3°C. Polyolefin adds 1°C. Any question involving Level A or B encapsulating suits should steer you toward physiological monitoring and strict work/rest limits, because WBGT alone is inadequate.

Tip 7: Memorize the acclimatization numbers. Full acclimatization: 7 to 14 days. New workers: 20 percent on day 1, add 20 percent per day. Returning experienced workers: 50, 60, 80, 100 percent. Loss begins after about one week away. A disproportionate share of heat deaths involve workers in their first week; the exam frequently asks about the highest-risk group.

Tip 8: Memorize the physiological monitoring limits. Sustained heart rate limit = 180 − age. Core temperature limit 38°C (unacclimatized or unscreened) or 38.5°C (acclimatized with medical supervision). Body weight loss not to exceed about 1.5 percent per shift. Hydration: about 8 oz every 15 to 20 minutes, not more than about 48 oz per hour.

Tip 9: Apply the hierarchy of controls. When asked for the best or most effective control, choose engineering (shielding radiant sources, ventilation, air conditioning, mechanization) over administrative (work/rest, acclimatization) over PPE (cooling vests). When asked which control reduces radiant heat specifically, choose reflective shielding, not fans. When air temperature exceeds about 35°C (95°F), fans can increase heat load; questions sometimes test this.

Tip 10: For cold stress, know the temperature triggers. Hypothermia begins below 35°C (95°F) core temperature. ACGIH: keep core above 36°C. Fine-dexterity hand warming below 16°C (60°F). Cover metal handles below −1°C (30°F). Heated shelters at −7°C (20°F) and below. Shivering stopping = moderate hypothermia = getting worse. Wet clothing and wind are the two biggest aggravating factors; cotton is the wrong base layer.

Tip 11: Distinguish the cold injuries by mechanism. Frostbite = freezing of tissue. Trench foot = prolonged wet and cold, above freezing. Chilblains = repeated cold exposure causing vessel inflammation, above freezing. Hypothermia = whole-body core temperature drop. If the scenario emphasizes wet feet for many hours at non-freezing temperatures, the answer is trench foot, not frostbite.

Tip 12: Watch the units. The exam may mix Celsius and Fahrenheit. Key conversions: 35°C = 95°F (hypothermia threshold), 38°C = 100.4°F (heat strain core limit), 40°C = 104°F (heat stroke), 16°C ≈ 60°F, −7°C ≈ 20°F, −1°C ≈ 30°F. Formula: °F = (°C × 1.8) + 32.

Tip 13: Recognize the regulatory framing. There is currently no final federal OSHA heat or cold standard; OSHA cites heat hazards under the General Duty Clause (Section 5(a)(1)) and references NIOSH criteria and ACGIH TLVs. OSHA has a National Emphasis Program on heat and a proposed heat injury and illness prevention rule. Several states have their own standards. OSHA 1910.141 (sanitation) requires potable water, and 1910.151 requires first aid provisions. If a question asks the legal basis for a federal heat citation, the answer is the General Duty Clause.

Tip 14: Read scenario questions for the limiting factor. Ask yourself: Is the problem metabolic (work too heavy), environmental (humidity, radiant load), clothing (vapor barrier), or individual (unacclimatized, medication, dehydration)? The correct answer typically addresses the dominant factor identified in the stem. If the stem mentions high humidity, the correct control attacks humidity or reduces workload, because evaporation is already compromised; adding more fans will not help much.

Tip 15: Use elimination on numeric answers. If you are unsure of an exact TLV value, use the pattern: heat TLVs for continuous work fall in the mid-to-high 20s°C for heavy and moderate work and about 31°C for light work. Any WBGT above about 32.5°C exceeds every TLV category; any WBGT below about 25°C is below every TLV for acclimatized workers in ordinary clothing. This lets you eliminate implausible options quickly.

9. Quick Reference Summary

• Heat balance: S = M ± C ± R ± K − E; evaporation is the only cooling route when air exceeds skin temperature.
• WBGT indoor: 0.7 T_nwb + 0.3 T_g; outdoor sun: 0.7 T_nwb + 0.2 T_g + 0.1 T_db.
• Heat illness severity: rash → cramps → syncope → exhaustion → stroke (altered mental status, core ≥ 40°C/104°F, emergency).
• TLV keeps core ≤ 38°C; Action Limit for unacclimatized; add clothing adjustment factor (vapor barrier +11°C).
• Acclimatization 7 to 14 days; 20 percent per day new; 50/60/80/100 percent returning; lost after about a week.
• Heart rate limit 180 − age; weight loss ≤ 1.5 percent; drink 8 oz every 15 to 20 minutes.
• Hypothermia core < 35°C/95°F; shivering stops in moderate stage; warm the core first, handle gently.
• Frostbite: do not rub, no direct heat, no thawing if refreezing possible; trench foot and chilblains occur above freezing.
• ACGIH cold: hand warming < 16°C for fine work; cover metal handles < −1°C; heated shelters ≤ −7°C; keep core ≥ 36°C.
• Controls: engineering (shielding, ventilation, heated enclosures) first, then administrative (work/rest, acclimatization, warm-up breaks), then PPE (cooling vests, layered cold-weather clothing).

Master these concepts, practice the WBGT arithmetic, and anchor every scenario question to the heat balance equation and the hierarchy of controls, and heat and cold stress questions on the ASP exam become reliable points.