B Part 16 Heat And Cold

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Heat And Cold

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B Part 16 Heat And Cold

  1. 1. Heat/Cold
  2. 2. Surrounding Temperature  Humidity  Air Velocity  Metabolic Rate  Clothing  Duration of Exposure 
  3. 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. 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. 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. 6. Wet Bulb Globe Temperature  Effective Temperature  Corrected Effective Temperature  Heat Stress Index  Predicted 4 Hour Sweat Rate  Wind Chill Index 
  7. 7. Most widely accepted heat stress index  Calculated from:  WBGT=0.7WB+0.3GT (indoors)   WBGT=0.7WB+0.2GT+0.1DB (outdoors)
  8. 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. 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. 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. 11. Uses the 6 thermal parameters to calculate a  nominal sweat rate that would be necessary to maintain thermal equilibrium
  12. 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. 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. 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. 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. 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. 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. 18. Work Organisation  Warm shelters   Dry clothing  Warm drinks  Close supervision  Avoid sweating by work organisation  Avoid sitting or standing still for long periods

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