Module 1: Occupational Hygiene - Section 5: Instrumentation

OH5.X7: Evaluation of Heat Stress - Heat-related Health Problems

Heat-related health problems:

Excessive exposure to hot work environments can bring about a variety of heat induced disorders.

Heat stress may lead to:

• Reduced work performance
• Increased risk of accidents
• Heat disorders

Low levels of heat stress may cause discomfort.

When heat stress exceeds a person's heat tolerance capacity, that may lead to adverse health effects (heat strain). The most critical heat-related disorders are:

• Prickly heat
• Heat cramps
• Heat exhaustion
• Heat stroke

Safety concerns:

Safety problems common to hot environments:

• Accidents
• Burns from accidental contact
• Irritability, anger and other emotional states.

Heat Stress Measurements

Heat stress is assessed by measuring climatic and physical factors, and then evaluating their effect on human body. The wet-bulb globe thermometer (WBGT) is the most commonly used and accepted means of measuring the effective temperature of a hot environment.

The WBGT correlates reasonably closely with physiological responses. WBGT is a heat stress index that combines the effects of humidity and air velocity (natural wet bulb temperature, TNWB); radiant heat (globe temperature, TG) and ambient air temperature (dry bulb temperature, TDB) into a single index. The index only measures what happens in the environment, does not indicate how the body will react.

WBGT Calculations:

Outdoors with solar load:	WBGT = 0.7 TNWB + 0.2 TG + 0.1 TDB
Outdoors without solar load:	WBGT = 0.7 TNWB + 0.3 TG

The WBGT index is used to determine the amount of rest necessary for any given workload by referring to the work/rest regimen schedule discussed in a further section.

General Introduction to Occupational Health: Occupational Hygiene, Epidemiology & Biostatistics by Prof Jonny Myers is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License.