Date post: | 20-May-2015 |
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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