Heat and Cold Stress

1. Why Heat and Cold Stress Matters for the CSP Exam and for Practice

Thermal stress is one of the most heavily tested topics in the BCSP CSP Occupational Health and Applied Science domain because it sits at the intersection of physiology, industrial hygiene measurement, exposure limits, the hierarchy of controls, emergency response, and regulation. In the field, heat is the leading weather-related cause of worker death in the United States, and a large share of victims are in their first days on the job. OSHA has no specific heat standard (a proposed rule exists, but enforcement currently relies on the General Duty Clause, Section 5(a)(1) and the National Emphasis Program on Outdoor and Indoor Heat-Related Hazards). Cold stress likewise has no OSHA-specific standard and is managed through recognized guidance from ACGIH and NIOSH. Because the CSP exam expects you to apply consensus guidance (ACGIH TLVs, NIOSH criteria documents) rather than a single regulation, you must understand the underlying science well enough to reason through scenario questions rather than memorize rule numbers.

2. What Heat Stress Is

Heat stress is the total heat load on the body from the combination of environmental heat (air temperature, humidity, radiant heat, air movement), metabolic heat from work, and clothing that restricts heat loss. Heat strain is the body's physiological response to that load (increased core temperature, heart rate, and sweating). The exam frequently tests this distinction: stress is the load; strain is the response.

The human body maintains a core temperature near 37°C (98.6°F). The heat balance equation describes the exchange:

S = M ± C ± R ± K − E

where S = heat storage, M = metabolic heat, C = convection, R = radiation, K = conduction, and E = evaporation. Metabolic heat is always a gain; convection, radiation, and conduction can be gains or losses depending on whether surrounding surfaces and air are hotter or cooler than skin (about 35°C / 95°F); evaporation is always a loss and is the body's primary cooling mechanism in hot conditions. High humidity suppresses evaporation, which is why humid heat is more dangerous than dry heat at the same air temperature. Vapor-barrier clothing (chemical suits, encapsulating PPE) effectively eliminates E and is a classic exam trigger for very high risk.

3. Heat-Related Illnesses (Recognize the Continuum)

Know these in order of increasing severity and their distinguishing features:

• Heat rash (prickly heat) – blocked sweat ducts; red bumps; keep skin dry and cool.
• Heat cramps – painful muscle spasms from salt loss with heavy sweating; rest, fluids with electrolytes.
• Heat syncope – fainting or dizziness from pooling of blood in the legs, usually after standing still or rising suddenly; lie down, cool, hydrate.
• Heat exhaustion – heavy sweating, weakness, headache, nausea, cool/clammy pale skin, rapid weak pulse, core temperature elevated but typically below 40°C (104°F). Mental status is normal or mildly impaired. Move to cool area, loosen clothing, give fluids if alert, monitor; seek medical care if no improvement.
• Heat stroke – a medical emergency. Core temperature at or above 40°C (104°F), altered mental status (confusion, slurred speech, loss of consciousness, seizures). Skin may be hot and dry (classic) or still sweating (exertional heat stroke in workers). Call 911 and begin aggressive, immediate cooling (ice water immersion if available, soaking with cold water and fanning, ice packs to neck, armpits, groin). The exam phrase to remember: cool first, transport second. Never give fluids by mouth to someone who is confused or unconscious.
• Rhabdomyolysis – muscle breakdown from heat and exertion; dark (tea-colored) urine, muscle pain; can cause kidney failure; requires medical evaluation.

The single most important diagnostic discriminator on exam questions is mental status: confusion or disorientation means heat stroke until proven otherwise, regardless of whether the person is sweating.

4. Measuring Heat Stress: WBGT and Related Indices

The Wet Bulb Globe Temperature (WBGT) is the index used by ACGIH, NIOSH, and ISO 7243 because it integrates the four environmental factors. Memorize both formulas:

Indoors or outdoors without solar load: WBGT = 0.7 T_nwb + 0.3 T_g
Outdoors with solar load: WBGT = 0.7 T_nwb + 0.2 T_g + 0.1 T_db

T_nwb = natural wet bulb temperature (a wetted thermometer exposed to natural air movement, representing evaporative cooling and humidity); T_g = globe temperature (a thermometer inside a 6-inch black copper sphere, representing radiant heat); T_db = dry bulb (ordinary air temperature). The natural wet bulb carries 70% of the weight, which emphasizes that humidity is the dominant factor.

Worked example: Outdoors in sun, T_nwb = 27°C, T_g = 40°C, T_db = 33°C. WBGT = (0.7 × 27) + (0.2 × 40) + (0.1 × 33) = 18.9 + 8.0 + 3.3 = 30.2°C.

When a worker moves between environments, a time-weighted average WBGT is calculated over the hour: WBGT_avg = (WBGT₁t₁ + WBGT₂t₂ + ...) / (t₁ + t₂ + ...).

Heat Index (National Weather Service) combines only air temperature and relative humidity and assumes shade and light wind. It is useful for public communication and the OSHA-NIOSH Heat Safety Tool app, but it is not a substitute for WBGT in occupational assessment because it ignores radiant load, air movement, metabolic rate, and clothing. If a question asks for the most appropriate index for a worker in direct sun wearing PPE, the answer is WBGT.

5. ACGIH TLV and Action Limit for Heat Stress

The ACGIH heat stress TLV is a screening table of WBGT values (°C) organized by metabolic rate category (light, moderate, heavy, very heavy) and work/rest allocation (e.g., 75–100% work, 50–75%, 25–50%, 0–25% work each hour). Two sets of values exist:

• TLV – applies to acclimatized workers.
• Action Limit (AL) – applies to unacclimatized workers and is roughly 2.5–3°C lower.

Pattern to remember: as metabolic rate rises or the work fraction increases, the allowable WBGT falls. For example, continuous light work for acclimatized workers is permitted at roughly 31°C WBGT, while continuous heavy work is limited to roughly 27.5°C (and lower still for unacclimatized workers). You will not be expected to recite every cell, but you must know how to read the table and which direction the numbers move.

Clothing adjustment factors are added to the measured WBGT before comparison with the TLV. Typical ACGIH values: work clothes (cotton) 0; cloth coveralls 0; double-layer woven clothing +3°C; SMS polypropylene coveralls +0.5°C; polyolefin coveralls +1°C; limited-use vapor-barrier coveralls +11°C. An exam item describing Level A or B chemical protective clothing is signaling that the screening table is inadequate and physiological monitoring is required.

Metabolic rate estimation (resting ~115 W, light ~180 W, moderate ~300 W, heavy ~415 W, very heavy ~520 W) is also fair game; a question describing shoveling, carrying heavy loads, or climbing is describing heavy or very heavy work.

6. Acclimatization

Acclimatization is the physiological adaptation that lowers heart rate and core temperature for a given load, increases sweat volume, and reduces salt in sweat. It develops over 7 to 14 days of progressively increasing exposure and is lost after roughly one week away (significant loss after 1 week; essentially gone after 3–4 weeks). NIOSH schedule: new workers start at no more than 20% of the usual duration of heat exposure on day one and increase by 20% each day; workers with prior experience in the job follow 50%, 60%, 80%, 100% over four days. Workers returning from vacation or illness must be re-acclimatized. Exam scenarios about a fatality in the first week of employment are testing acclimatization.

7. Physiological Monitoring (Heat Strain)

When clothing or conditions exceed the screening criteria, the ACGIH TLV recommends monitoring heat strain. Common exam thresholds:
• Sustained heart rate over several minutes exceeding 180 minus age (beats/min).
• Core body temperature exceeding 38.5°C (101.3°F) for medically selected, acclimatized workers, or 38°C (100.4°F) for unselected, unacclimatized workers.
• Recovery heart rate one minute after a peak effort above about 120 bpm (older guidance used 110).
• Symptoms of sudden severe fatigue, nausea, dizziness, or lightheadedness.
• Profuse sweating over hours or weight loss exceeding 1.5% of body weight in a shift indicates dehydration.
Any of these means the exposure must be discontinued or controlled.

8. Controlling Heat Stress (Apply the Hierarchy)

Engineering controls (preferred): general dilution ventilation; local spot cooling and fans (fans help only when air temperature is below about 35°C / 95°F and humidity is not extreme; above that they add convective heat); air conditioning of control rooms and rest areas; radiant heat shielding and insulation of hot surfaces; reducing humidity by eliminating steam leaks and open hot water; mechanization to cut metabolic load.

Administrative controls: work/rest schedules in a cool area; scheduling heavy work for cooler parts of the day; acclimatization programs; hydration (about 1 cup / 8 oz of cool water every 15–20 minutes, not exceeding roughly 48 oz per hour, with electrolytes for prolonged sweating over 2 hours); buddy system and supervision; training on symptoms and first aid; medical surveillance and screening of medications and conditions that increase risk (diuretics, antihistamines, beta blockers, prior heat illness, obesity, poor fitness).

PPE (last line): reflective aprons for radiant heat; cooling vests (ice, phase-change, or circulating liquid); vortex-cooled or air-supplied suits for encapsulating work. Remember that most PPE increases heat stress, so the exam often frames PPE as a hazard to be accounted for, not a solution.

9. What Cold Stress Is

Cold stress occurs when the environment removes heat faster than the body can produce it, driving skin and eventually core temperature downward. Heat loss mechanisms are the same as in the heat balance equation: conduction (water conducts heat about 25 times faster than air, so wet clothing and immersion are critical), convection (wind), radiation (especially from an uncovered head), evaporation (sweat and wet clothing), and respiration. Wind chill expresses the combined cooling effect of air temperature and wind speed as an equivalent still-air temperature; it predicts frostbite risk on exposed skin but does not lower the actual temperature of objects below the air temperature.

10. Cold-Related Illnesses

• Hypothermia – core temperature below 35°C (95°F). Mild: shivering, loss of fine motor skills, 'umbles' (mumbles, stumbles, fumbles). Moderate: violent shivering that then stops, confusion, slurred speech, poor judgment (paradoxical undressing). Severe: unconsciousness, weak or absent pulse, cardiac arrhythmia. Cessation of shivering with worsening mental status is a danger sign, not improvement. Treatment: move to warmth, remove wet clothing, insulate (including head and neck), warm the core (trunk, armpits, groin) before extremities, give warm sweet drinks only if alert, handle very gently to avoid triggering ventricular fibrillation, and call EMS. Do not rub extremities or apply direct high heat.
• Frostbite – freezing of tissue, typically fingers, toes, nose, ears, cheeks. Numbness, waxy white or grayish skin, hard to the touch. Do not rub, do not use dry heat, and do not rewarm if there is any risk of refreezing. Rewarm in water at about 37–39°C (99–102°F) or seek medical care.
• Trench foot (immersion foot) – prolonged exposure to wet, cold (not necessarily freezing) conditions; tingling, numbness, swelling, blisters. Prevention is keeping feet dry and changing socks.
• Chilblains – repeated exposure of skin to cold above freezing causing inflammation, redness, itching, and blistering.

11. ACGIH Cold Stress TLV and Guidance

Key points the exam draws from the ACGIH cold stress TLV:
• The objective is to prevent deep body temperature from falling below 36°C (96.8°F) and to prevent cold injury to extremities.
• For work below 16°C (60.8°F) involving sedentary or fine manual tasks, measures to keep hands warm are needed.
• Below 4°C (40°F) workers in wet or sweat-soaked clothing should change immediately; below about −7°C (20°F) with wind, continuous exposure of exposed skin should not be permitted.
• At or below −7°C (20°F), metal tool handles and bars should be insulated and gloves or mittens are required; eye protection for blowing snow and ice.
• At air temperatures below about −12°C (10°F) equivalent chill temperature, the work/warm-up schedule applies: for a 4-hour shift, maximum work periods shrink and the number of mandatory warm-up breaks (in a heated shelter) increases as temperature drops and wind rises; non-emergency work ceases at very low equivalent temperatures (around −45°C / −50°F equivalent).
• Workers should be under constant protective observation (buddy system) and the work rate should be set to avoid heavy sweating.

12. Controlling Cold Stress

Engineering: heated shelters and warming stations, windbreaks, radiant heaters, insulating metal surfaces, heated tool handles, enclosing cabs. Administrative: work/warm-up schedules, scheduling outdoor work during warmer parts of the day, acclimatization to cold (less robust than heat acclimatization), monitoring weather and wind chill, buddy system, training, avoidance of alcohol (causes vasodilation and heat loss) and limiting caffeine and nicotine (vasoconstriction, dehydration), warm caloric fluids and adequate food intake. PPE: the three-layer system – a moisture-wicking inner layer (synthetic or wool, never cotton next to skin), an insulating middle layer, and a wind- and water-resistant outer layer; insulated, waterproof boots with room for sock layers; hat covering ears (large heat loss from the head); mittens are warmer than gloves; spare dry clothing available on site.

13. Regulatory and Reference Framework

• OSHA: no specific heat or cold standard; enforcement via the General Duty Clause (recognized hazard, causing or likely to cause death or serious harm, feasible means of abatement), the Heat NEP, and related standards such as 29 CFR 1910.141 (potable water), 1910.151 (medical and first aid), and 1926.51. A proposed rule, Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings, uses an initial heat trigger of 80°F heat index and a high heat trigger of 90°F heat index.
• NIOSH: Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (2016) with Recommended Exposure Limits (RELs) for acclimatized workers and Recommended Alert Limits (RALs) for unacclimatized workers, plus the cold stress guidance.
• ACGIH: TLVs for Heat Stress and Strain and for Cold Stress (published annually).
• Several states (California, Washington, Oregon, Minnesota, Colorado, Maryland) have their own heat standards; California's standard triggers at 80°F for shade provision and 95°F for high-heat procedures.

14. How to Answer Exam Questions on Heat and Cold Stress

Use a four-step approach for any thermal stress item:

Step 1 – Classify the question. Is it (a) a calculation (WBGT, time-weighted average, unit conversion, work/rest ratio), (b) recognition of an illness or strain indicator, (c) selection of a control or program element, (d) measurement method or index selection, or (e) regulatory basis? Each type has a predictable logic.

Step 2 – Extract the clues. Note sun vs. shade, humidity, radiant sources, metabolic category from the task description, clothing type, acclimatization status (new hire, returned from leave), and mental status of a victim. These clues, not the surface wording, determine the answer.

Step 3 – Apply the science or the table logic. For calculations, write the formula first, convert units so everything is consistent, and check that the answer is physically reasonable (WBGT must fall between the wet bulb and the globe temperature). For controls, apply the hierarchy and pick the most protective feasible option. For illness, decide on severity by mental status and core temperature.

Step 4 – Eliminate distractors. Wrong answers typically substitute heat index for WBGT, reverse heat exhaustion and heat stroke, recommend transporting a heat stroke victim before cooling, suggest rubbing frostbitten tissue, or offer PPE where an engineering control is available.

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

• Memorize both WBGT formulas and the 0.7 weighting on natural wet bulb. If a question omits a solar load or says indoors, use the two-term formula. Check: the coefficients sum to 1.0.
• Watch temperature units. ACGIH tables are in °C; many scenarios are in °F. °C = (°F − 32) / 1.8 and °F = 1.8 × °C + 32. A single unit slip is the most common calculation error.
• Unacclimatized = Action Limit; acclimatized = TLV. New hires, workers back from a week or more off, and workers during a sudden heat wave are treated as unacclimatized.
• Heavier work means lower allowable WBGT. If an answer choice shows the allowable WBGT increasing with workload, it is wrong.
• Clothing adjustments are added to the measured WBGT, not subtracted from the TLV; vapor-barrier ensembles (+11°C) mean screening is inadequate and physiological monitoring is required.
• Mental status is the tie-breaker between heat exhaustion and heat stroke. 'Confused,' 'disoriented,' or 'collapsed and unresponsive' equals heat stroke, even if the worker is sweating.
• For heat stroke: call EMS and cool immediately and aggressively (cold water immersion is the gold standard); for an unconscious person, never give oral fluids.
• Fans are not always a control. Above about 35°C (95°F) or in very high humidity, fans increase convective heat gain; air conditioning, shielding, or ventilation with cooler outside air is better.
• Hydration guidance: about 8 oz every 15–20 minutes; do not exceed roughly 48 oz per hour (hyponatremia risk); electrolytes for sustained sweating beyond about two hours. Thirst is a lagging indicator.
• Heart rate thresholds: sustained heart rate above 180 minus age, or recovery heart rate above about 120 after one minute, is a strain indicator that requires stopping the exposure.
• Cold: never rub frostbite, never rewarm if refreezing is possible, never give alcohol. Handle hypothermia victims gently, remove wet clothing, warm the core first, and treat cessation of shivering as deterioration.
• Wind chill predicts the rate of heat loss from exposed skin; it does not cool objects or water below the actual air temperature.
• Layering and fabric: wicking synthetic or wool base layer, insulating middle, windproof/waterproof shell; cotton is the wrong answer for a base layer because it holds moisture.
• Regulatory anchor: if a question asks what OSHA would cite in a heat fatality, the answer is the General Duty Clause, Section 5(a)(1), supported by recognized guidance such as the ACGIH TLV and NIOSH criteria document.
• Program questions: a complete heat illness prevention program includes written procedures, hazard assessment (WBGT monitoring), acclimatization, water/rest/shade, training, supervision and buddy system, emergency response, and medical surveillance. If a choice lists only one element as 'sufficient,' it is a distractor.
• Read for the word 'most' or 'first.' 'Most effective' points to engineering controls or elimination; 'first action' for a collapsed worker in heat points to activating EMS and initiating cooling; 'first step' in program development points to hazard assessment.
• Do not overthink table values. The exam rewards understanding of trends and relationships (humidity reduces evaporation, acclimatization raises tolerance, PPE increases load, wind increases cold loss) far more than exact recall of a single WBGT cell.

16. Quick Reference Summary

• Heat balance: S = M ± C ± R ± K − E; evaporation is the main cooling path.
• WBGT indoors: 0.7 NWB + 0.3 GT; outdoors with sun: 0.7 NWB + 0.2 GT + 0.1 DB.
• ACGIH TLV (acclimatized) vs Action Limit (unacclimatized); clothing adjustment added to WBGT.
• Acclimatization 7–14 days; NIOSH 20% rule for new workers; lost after about a week away.
• Strain limits: HR > 180 − age sustained; core > 38.5°C (38.0°C unacclimatized); recovery HR > 120.
• Heat stroke = core ≥ 40°C + altered mental status; cool first, transport second.
• Hypothermia = core < 35°C; frostbite = frozen tissue; trench foot = wet cold above freezing.
• Cold TLV: protect core ≥ 36°C; insulate metal handles below −7°C; work/warm-up schedule as equivalent chill temperature falls.
• Controls follow the hierarchy: engineering, administrative, PPE; most PPE increases heat stress.
• Regulatory basis in the U.S.: OSHA General Duty Clause and Heat NEP, ACGIH TLVs, NIOSH REL/RAL, and state standards.

Master these relationships, practice two or three WBGT calculations until the formulas are automatic, and approach every scenario by identifying the clues (environment, workload, clothing, acclimatization, mental status) before looking at the answer choices. That discipline will carry you through virtually any heat or cold stress item on the CSP exam.