Heat stress
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An introduction to risks from exposure to heat in the workplace, assessment methods and the management and control of the risks
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Heat stress
- 7. Convection
- 11. Heat Balance Equation M = E + C + R
- 12. > 43 Tissue damage - Death 40 - 43 Failure of sweating mechanism 38 - 40 Limit set by WHO for avoidance of physiological strain 36.4 - 37.6 Normal core temperature 34 - 36.4 Shivering, decreased efficiency, confusion 30 - 34 Drowsiness, irregular heart rate, cramp 26 - 30 Loss of consciousness, severe impairment of respiratory and cardiac functions < 26 Death
- 13. Hypothalamus Exercise Shivering Vasomotor Sweating Endocrine Behaviour Skin temp. Core Temp CNS Temp Controlled System (heat capacitance) ENVIRONMENT
- 14. Source: WHO
- 15. Heat stroke Body becomes unable to control its temperature
- 16. Heat stroke Death or permanent damage may occur if treatment is not given promptly
- 17. Heat stroke - early signs Body temperature raised Erratic behaviour Irritable Hot, dry, flushed skin Weakness Unsteady
- 18. Fully developed heat stroke Flushed Dry skin Convulsions Loss of consciousness Body temperature 40 C or above
- 19. Heat exhaustion Caused by excessive loss of water and/or salt due to sweating
- 20. Heat exhaustion Pale moist face Dizziness / nausea and vomiting Headache and fatigue Oral temperature normal or slightly elevated
- 21. Heat exhaustion May collapse if warning signs ignored
- 22. Heat cramps Painful muscle spasms Caused by loss of salt due to sweating
- 23. Heat syncope Dilation of blood vessels Blood pools in capillaries Brain deprived of oxygen Fainting
- 24. Heat rash Blocking of pores by sweat
- 25. Heat rash Skin rash over arms, shoulders, chest and behind knees Tingling or pricking feeling on skin
- 26. Factors that can lead to an increased risk include: Impervious clothing Alcohol Medication Poor physical fitness Obesity
- 27. Other effects Contact with hot surfaces Psychological effects – increased incidence of accidents
- 29. Heat Balance Equation M = E + C + R
- 30. Heat Balance Equation M = E + C + R Work rate
- 31. Heat Balance Equation M = E + C + R Air temp Air velocity
- 32. Heat Balance Equation M = E + C + R Mean radiant temperature
- 33. Radiant heat exchange R = T4 R = Radiant heat in W/m2 = Stefan-Boltzman constant = emissivity T = surface temperature in K
- 34. Emissivity Brass - polished 0.026 - 0.07 Brass - dull 0.6 Copper - polished 0.026 - 0.07 Copper - dull 0.6 - 0.88 Aluminium - polished 0.026 - 0.07 Aluminium - dull 0.07 - 0.086 Stainless steel - polished (monel) 0.09 Stainless steel - oxidised (monel) 0.43 Glass 0.72 - 0.87 Brick 0.93 - 0.95 Cast Iron 0.94 Soot 0.96 Black Body 1
- 36. Heat Balance Equation M = E + C + R Humidity Air velocity
- 37. Heat Balance Equation M = E + C + R Humidity Air velocity Air temp Air velocity Mean radiant temperature Work rate
- 38. Heat Balance Equation M = E + C + R Humidity Air velocity Air temp Air velocity Mean radiant temperature Work rate Clothing
- 41. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate
- 42. Acclimatisation Physiological adaption to heat Can develop after 10 to 14 days exposure to hot conditions
- 43. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate Acclimatisation
- 46. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate Acclimatisation
- 50. Mini-globe
- 53. Metabolic rate 1 Met = 58 Wm-2
- 54. Clothing 1 Clo = Insulation value of 0,155 m2 oC/W
- 55. Acclimatisation YES ? OR NO?
- 57. Screening methods Talking to people Observations Checklists
- 60. WBGT Index Indoors WBGT = 0.7 tnwb + 0.3 tg Outdoors WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta
- 61. WBGT Reference Values from ISO 7243 Metabolic Rate Class Metabolic Rate W/m2 Reference Value of WBGT (C) Acclimatised Non-acclimatised 0 <65 33 32 1 65 - 130 30 29 2 130 - 200 28 28 3 200 - 260 no air movement 25 with air movement 26 no air movement 22 with air movement 23 4 >260 no air movement 23 with air movement 25 no air movement 18 with air movement 20
- 62. ACGIH TLVs – Action Limit Allocation of work in work cycle Workload Light Moderate Heavy V ery heavy 75% to 100% 28.0 25.0 - - 50% to 75% 28.5 26.0 24.0 - 25% to 50% 29.5 27.0 25.5 24.5 0 to 25% 30.0 29.0 28.0 27.0
- 63. ACGIH TLVs Allocation of work in work cycle Workload Light Moderate Heavy V ery heavy 75% to 100% 31.0 28.0 - - 50% to 75% 31.0 29.0 27.5 - 25% to 50% 32.0 30.0 29.0 28.0 0 to 25% 32.5 31.5 30.5 30.0
- 64. TLV Clothing Corrections ClothingType WBGT Correction Work clothes (long sleeve and pants) 0 Cloth (woven material) coveralls o Double layer woven clothing 3 SMS polypropylene coveralls 0.5 Polyolefin overalls 1 Limited use capour-barrier overalls 11
- 65. ISO Standards 7243 Estimation of heat stress usingWBGT 7730 Evaluation of moderate thermal environments using PMV and PPD 7933 Analytical determination of heat stress using the Predicted Heat Strain Index 7726 Instruments and methods 8996 Physiological methods
- 66. Predicted Heat Strain Index Complex! Based on heat balance equation Solve using computer program
- 69. Predicted Heat Strain Index Gives maximum allowable exposure times based on o Heat storage o Water loss
- 70. Outdated heat stress indices Effective temperature (ET) Corrected effective temperature (CET) Predicted four hour sweat rate (P4SR) The heat stress index (HSI) Index of thermal stress (ITS)
- 72. Miner’s Core Temperature & Heart Rate Source: OHTA.
- 73. Personal Monitor
- 74. Assess Risk using screening methods WBGT Index ISO 7243 or ACGIH TLVs Expert analysis PHS Index - ISO 7933 Expert analysis Physiological measures – ISO 9886 ISO 27726 Specification of equipment used to measure thermal environment ISO 28996 Estimation or measurement of Metabolic rate Identify Hazards Identify Controls A Structured Approach to Heat Stress Risk Assessment
- 76. Hierarchy of Control Prevention Engineering Work Practices PPE
- 77. Occupational Health Management Prevention Engineering Work Practices PPE Supervision Maintenance Procedures Auditing Testing Health surveillance Monitoring Information Training Housekeeping
- 78. Metabolic Rate Automate Reduce work rate Mechanical aids
- 79. Radiant Heat Exchange R = T4 R = Radiant heat in W/m2 = Stefan-Boltzmann constant = emissivity T = surface temperature in K
- 80. Controlling Radiant Heat R = T4 Reduce temperature
- 81. Controlling Radiant Heat R = T4 Reduce temperature Minimise size / intensity of source Insulate surfaces Direct / indirect cooling
- 82. www.lubisol.com
- 83. Controlling Radiant Heat R = T4 Reduce emissivity
- 84. Controlling Radiant Heat R = T4 Reduce emissivity Cladding Bright, shiny surfaces e.g. Polished aluminium
- 88. Reflective shielding for radiant heat
- 90. Increase air movement Be careful as this can increase convective heat gain
- 91. Local cooling Introducing pre-cooled air http://mikegigi.com
- 92. General ventilation cool air enters at low level through open windows Hot air escapes through roof vent hot process
- 93. High humidity Extract humid air Dehumidification Increase air movement
- 94. Time Reduce exposure time Job rotation Work – rest regimes Work scheduling Distance Segregation Restrict access Rest areas Organisation Reduce numbers exposed Good working practice Written procedures “Permits to work” Work practices / organisation
- 97. Cooling vests
- 99. Management measures Screening & health surveillance Information, instruction, training Supervision Self regulation Provide water
- 104. • ISO 7730 (Thermal comfort) • ISO 7743 (WBGT) • ISO 7933 (Heat stress) Standards
- 105. Picture credits Stock.xchng (www.sxc.hu) LumaSense Technologies (www.innova.dk) Occupational hygiene training association (www.ohlearning.com) Lubisol (www.lubisol.com) Industrial Heating magazine (www.industrialheating.com) Northwest Ohio railway preservation inc (www.nworrp.org) Mike Firth's Revised Again Glassblowing Homepage (http://mikegigi.com)