2. Surrounding Temperature
Humidity
Air Velocity
Metabolic Rate
Clothing
Duration of Exposure
3. Dry Bulb Air Temperature
Measured in glass thermometers, thermocouples or
resistance thermometers
Sensing head protected from radiant heat by a polished
silver or aluminium shield
Wet Bulb Air Temperature
Sensing head covered by muslin sock wetted with distilled
water and protected from radiant heat
Globe Temperature
Measures radiant temperature
Hollow copper sphere painted matt black, into which a
thermometer is inserted with bulb at centre of globe
4. Colour Indicating Temperature
Systems
Thermal Crayons or Paints
Enables temp. of entire surface to be
given at a glance
Reversible or irreversible effects
Temperature Indicating Strips
110oC
Adhesive strip with 8 or 9 dots
104oC
sensitive to temperature Unchanged
99oC dots
As temperature rises, black dots
93oC
occur
88oC
Can be kept for record purposes Dots changed
82oC
to black by
77oC heating
71oC
5. Kata Thermometer
Used to determine wind velocities
Used in conjunction with nomographs which relate cooling
time to wind velocity
Humidity
Measure of concentration of water vapour in atmosphere
Where maximum vapour pressure occurs, air is said to be
saturated
Relative humidity is a ratio expressed as %
Measured by a hygrometer
6. Wet Bulb Globe Temperature
Effective Temperature
Corrected Effective Temperature
Heat Stress Index
Predicted 4 Hour Sweat Rate
Wind Chill Index
7. Most widely accepted heat stress index
Calculated from:
WBGT=0.7WB+0.3GT (indoors)
WBGT=0.7WB+0.2GT+0.1DB (outdoors)
8. Takes into account wet bulb temperature, dry
bulb temperature and air velocity
Derived from studies on US marines
Scale takes into account thermal conditions and
two levels of clothing:
Lightly clad
Stripped to the waist
9. Uses same principles as ET but corrects index
to take account of radiant heat, so globe
temperature is used instead of dry bulb
temperature
10. Aims to predict thermal effects on body by
balancing heat inputs (from environment and
metabolic rate) against heat loss by the
evaporation of sweat
Expressed as a no. between 1 and 100
Conditions below 40 pose no risk
Above 40 the risk increases
100 represents situation where heat gain just
matches that lost by evaporation
Over 100 there is a net heat gain to the body
11. Uses the 6 thermal parameters to calculate a
nominal sweat rate that would be necessary to
maintain thermal equilibrium
12. Index of heat loss from the body developed to
quantify risk resulting from combined cooling
effect of wind and cold conditions
There is an effective “chilling temperature”
which is defined as the ambient temperature
that produces the same effect in still air as the
actual environmental conditions
13. Heat Stress: Cold Stress
Furnace work Outdoor work
Glass-making Sea fishing
Welding, brazing Shipping
Boiler work Oil rigs
Deep mining Deep freeze rooms
Laundries Cold stores
Kitchens Diving
Fire fighting
14. Environmental control:
Lower temperature of heat source
Surface insulation
Ventilation
Increased air velocity
Fine water sprays (can increase humidity)
Radiation barriers between heat source and worker
15. Work Organisation
Reduced time exposure
Length of work and rest periods derived from
appropriate heat stress indices
Adequate supervision to ensure that work regimes
are followed and that potential heat stress is detected
at an early stage
16. Person
PPE
Heat-resistant clothing
Ice-cooled jackets, air cooled or water cooled suits
Take care that problem is not made worse!
Plenty of drinks, salt tablets
Information, Instruction and Training
17. Clothing:
Thermal insulation
Outer tightly woven layer that is windproof
Waterproofing for cold wet environments
Semi-permeable fabrics may be needed for active
personnel where clothing must be waterproof and
windproof but also allow perspiration to escape
18. Work Organisation
Warm shelters
Dry clothing
Warm drinks
Close supervision
Avoid sweating by work organisation
Avoid sitting or standing still for long periods
