Heat/Cold

Surrounding Temperature

Humidity

Air Velocity

Metabolic Rate

Clothing

Duration of Exposure

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

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

Adhesive strip with 8 or 9 dots sensitive to temperature

As temperature rises, black dots occur

Can be kept for record purposes

Unchanged

dots

Dots changed

to black by

heating

110oC

104oC

99oC

93oC

88oC

82oC

77oC

71oC

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

Wet Bulb Globe Temperature

Effective Temperature

Corrected Effective Temperature

Heat Stress Index

Predicted 4 Hour Sweat Rate

Wind Chill Index

Most widely accepted heat stress index

Calculated from:

WBGT=0.7WB+0.3GT (indoors)

WBGT=0.7WB+0.2GT+0.1DB (outdoors)

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

Uses same principles as ET but corrects index to take account of radiant heat, so globe temperature is used instead of dry bulb temperature

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

Uses the 6 thermal parameters to calculate a nominal sweat rate that would be necessary to maintain thermal equilibrium

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

Heat Stress:

Furnace work

Glass-making

Welding, brazing

Boiler work

Deep mining

Laundries

Kitchens

Fire fighting

Cold Stress

Outdoor work

Sea fishing

Shipping

Oil rigs

Deep freeze rooms

Cold stores

Diving

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

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

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

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

Work Organisation

Warm shelters

Dry clothing

Warm drinks

Close supervision

Avoid sweating by work organisation

Avoid sitting or standing still for long periods