heat stress

1. EVALUATION OF HEAT STRESS

2. What is Heat Stress?
Heat stress is a condition in which net heat load on your
body from internal heat production and external sources
exceeds your body’s capacity to cool itself.
Temperature > 37.6 degree Celsius

3. Measurement of heat stress
Metabolic Factors
 Direct and Indirect Calorimetry
Environmental Factors
 Air temperature
 Air humidity
 Air velocity
 Radiant heat
Psychrometer
Katathermometer
Globe Thermometer

4. Human Heat Balance Equation
Where
R = Radiant heat
C = Conductive heat
E = Evaporative heat
S = Storage heat
M = Metabolic heat

5. Heat Stress Indices
1. Effective Temperature : Sensory scale of warmth, compiled from the readings of dry & wet
bulb temperature and air velocity from temperature and standard nomogram. Safe Limit is
30 degree Celsius
2. Corrected Effective Temperature: The effects of radiant heat can be included in an
assessment of effective temperature by using the globe thermometer temperature instead
of the dry-bulb temperature in those cases when the reading of the globe thermometer is
higher than the dry-bulb temperature. In such cases, the result is described as the
corrected effective temperature. Safe Limit is 29 degree Celsius.
3. Predicted 4-hour Sweat Rate: The amount of sweat that would be perspired by a
physically fit and acclimatized young man in the condition under review oral period of 4
hours. It takes into account the metabolic level and type of clothing in addition to the
climatic factors unlike other indices mentioned earlier. Normal Range 2.5 – 3 Liters per 4
hours

6. Continuation……
4. Belding – Hatch Index: Safe limit is 24 units, if more than 24 units muscular activity should
be discontinued.
5. Oxford Index: It is used to assess the severity of hot humid conditions of the working place
where ventilation is poor.
WD = 0.15d + 0.85 w
Where, WD= Weighted value, d&w= dry & wet bulb temperature
5. Wet Bulb Globe Temperature (WBGT) Index: It embraces in a single value the effect of
‘radiation’, ‘ambient air temperature’ and ‘humidity’. Safe Limit 30 degree Celsius.
Exposure to Sunlight = WBGT = 0.7wb+0.2 gt+0.1db
Non Exposure to Sunlight = WBGT = 0.7wb+0.3gt
Where, db =dry bulb
Advantage: It excludes the use of anemometers and eliminates the problem of obtaining
average air velocity.