Thermal Stressors

What are thermal stressors?

Environmental conditions that add or remove heat from the body, potentially disrupting thermal balance and causing heat- or cold-related illness.

What is the goal of thermal regulation in the body?

Maintain thermal balance so core body temperature remains stable.

What are the main components of heat balance?

Metabolic heat, evaporative cooling, conduction, convection, radiation, and heat storage

What is metabolic heat?

Heat generated by the body as food is converted into energy and mechanical work during physical activity.

How is metabolic heat related to mechanical work?

Metabolic heat = metabolic energy − mechanical work (M − W).

What is evaporative cooling?

Heat loss through evaporation of sweat from the skin; it is endothermic and removes heat from the body.

Why does high humidity reduce evaporative cooling?

Moist air limits evaporation, so sweat does not evaporate efficiently, reducing heat loss.

Why does dry heat feel more tolerable than humid heat?

Lower humidity allows more sweat evaporation, improving evaporative cooling.

What are the three primary modes of heat transfer?

Conduction, convection, and radiation.

What is conduction?

Direct heat transfer through physical contact with another surface or object.

What is convection?

Heat transfer through moving air or liquid across the skin.

What is radiation?

Heat transfer via electromagnetic waves, such as heat from the sun or hot equipment.

Write the thermal balance equation.

ΔS = M ± C ± K ± R − E

What does ΔS represent in the thermal balance equation?

Change in body heat content (heat storage).

What does ΔS = 0 indicate?

Body is in thermal balance.

What is heat stress?

The total environmental and metabolic heat load imposed on the body.

What is heat strain?

The physiological response of the body to heat stress.

Why is heat stress not the same as heat strain?

Heat stress is the hazard; heat strain is the body’s response to that hazard.

Why is air temperature alone insufficient to assess heat stress?

Radiant heat, humidity, air movement, and workload also affect heat stress.

What is acclimatization?

Gradual physiological adaptation that improves tolerance to heat stress.

How long does heat acclimatization typically take?

Approximately 7–14 days.

What physiological changes occur with acclimatization?

Earlier sweating, increased sweat production, increased skin blood flow, improved sweating efficiency.

What is a sign of excessive heat strain related to heart rate?

Sustained heart rate > (180 bpm − age).

What core body temperature indicates excessive heat strain?

Greater than 38.5°C.

What recovery heart rate indicates unacceptable heat strain?

Heart rate >120 bpm after one minute of rest.

What symptoms may indicate heat strain?

Fatigue, nausea, dizziness, headache, excessive sweating.

What are acute heat disorders?

Heat rash, heat cramps, heat exhaustion, heat stroke, heat syncope.

What is heat exhaustion?

A serious condition caused by water and/or salt depletion and heavy sweating.

What is heat stroke?

A medical emergency where temperature regulation fails and core temperature rises dangerously.

Key symptoms of heat stroke.

Altered mental status, confusion, convulsions, possible lack of sweating

Immediate response to suspected heat stroke.

Call emergency services and rapidly cool the individual.

What is cold stress?

Excessive loss of body heat due to cold environmental conditions.

What is equivalent chill temperature (wind chill)?

A measure of perceived cold that accounts for air temperature and wind speed.

Why does wind increase cold stress?

Wind increases convective heat loss from the skin.

Why is wet clothing dangerous in cold environments?

It increases conductive and evaporative heat loss and reduces insulation.

What is hypothermia?

A condition where core body temperature drops below normal.

At what core temperature does shivering typically stop?

Around 35°C (95°F).

Who is at increased risk for hypothermia?

Older adults and individuals with alcohol or drug use.

What are peripheral cold injuries?

Localized tissue injuries such as frostbite and chilblains.

What is frostbite?

Tissue damage caused by freezing of skin and underlying tissues.

What are chilblains?

Painful inflammation from prolonged exposure to cold without freezing.

Body attempts to reject heat via cutaneous vasodilation

Heat strain.

Exposure guidelines commonly recommend keeping CBT between:

36-38 C

Hypothermia is a risk when CBT goes below

35C

Hyperthermia (heat stroke) is a risk when CBT approaches

43 C