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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  • Great Power Point on heat stress! Thank you. Here’s a link to another great free resource on heat stress - http://www.safetyawakenings.com/11-cool-tips-for-working-in-extreme-heat/
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Heat stress

  1. 1. Convection
  2. 2. Radiation Convection
  3. 3. Radiation Convection Evaporation
  4. 4. Radiation Convection Evaporation
  5. 5. Heat Balance Equation M = E + C + R
  6. 6. > 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
  7. 7. Hypothalamus Exercise Shivering Vasomotor Sweating Endocrine Behaviour Skin temp. Core Temp CNS Temp Controlled System (heat capacitance) ENVIRONMENT
  8. 8. Source: WHO
  9. 9. Heat stroke Body becomes unable to control its temperature
  10. 10. Heat stroke Death or permanent damage may occur if treatment is not given promptly
  11. 11. Heat stroke - early signs Body temperature raised Erratic behaviour Irritable Hot, dry, flushed skin Weakness Unsteady
  12. 12. Fully developed heat stroke Flushed Dry skin Convulsions Loss of consciousness Body temperature 40 C or above
  13. 13. Heat exhaustion Caused by excessive loss of water and/or salt due to sweating
  14. 14. Heat exhaustion  Pale moist face  Dizziness / nausea and vomiting  Headache and fatigue  Oral temperature normal or slightly elevated
  15. 15. Heat exhaustion May collapse if warning signs ignored
  16. 16. Heat cramps Painful muscle spasms Caused by loss of salt due to sweating
  17. 17. Heat syncope Dilation of blood vessels Blood pools in capillaries Brain deprived of oxygen Fainting
  18. 18. Heat rash Blocking of pores by sweat
  19. 19. Heat rash Skin rash over arms, shoulders, chest and behind knees Tingling or pricking feeling on skin
  20. 20. Factors that can lead to an increased risk include: Impervious clothing Alcohol Medication Poor physical fitness Obesity
  21. 21. Other effects Contact with hot surfaces Psychological effects – increased incidence of accidents
  22. 22. Radiation Convection Evaporation
  23. 23. Heat Balance Equation M = E + C + R
  24. 24. Heat Balance Equation M = E + C + R Work rate
  25. 25. Heat Balance Equation M = E + C + R Air temp Air velocity
  26. 26. Heat Balance Equation M = E + C + R Mean radiant temperature
  27. 27. Radiant heat exchange R = T4 R = Radiant heat in W/m2  = Stefan-Boltzman constant  = emissivity T = surface temperature in K
  28. 28. 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
  29. 29. Mean radiant temperature
  30. 30. Heat Balance Equation M = E + C + R Humidity Air velocity
  31. 31. Heat Balance Equation M = E + C + R Humidity Air velocity Air temp Air velocity Mean radiant temperature Work rate
  32. 32. Heat Balance Equation M = E + C + R Humidity Air velocity Air temp Air velocity Mean radiant temperature Work rate Clothing
  33. 33. Air temperature Mean radiant temperature Humidity Air velocity
  34. 34. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate
  35. 35. Acclimatisation Physiological adaption to heat Can develop after 10 to 14 days exposure to hot conditions
  36. 36. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate Acclimatisation
  37. 37. Air temperature Mean radiant temperature Humidity Air velocity
  38. 38. Air temperature Mean radiant temperature Humidity Air velocity Clothing Metabolic rate Acclimatisation
  39. 39. Air temperature Standard thermometer
  40. 40. Humidity Whirling hygrometer
  41. 41. Radiant heat Globe thermometer
  42. 42. Mini-globe
  43. 43. Air velocity Kata thermometer
  44. 44. Electronic instruments
  45. 45. Metabolic rate 1 Met = 58 Wm-2
  46. 46. Clothing 1 Clo = Insulation value of 0,155 m2 oC/W
  47. 47. Acclimatisation YES ? OR NO?
  48. 48. Heat stress index Air temp. Mean radiant temp. Humidity Air movement Work rate Clothing Acclimn
  49. 49. Screening methods Talking to people Observations Checklists
  50. 50. WBGT Index Indoors WBGT = 0.7 tnwb + 0.3 tg Outdoors WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta
  51. 51. 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
  52. 52. 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
  53. 53. 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
  54. 54. 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
  55. 55. 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
  56. 56. Predicted Heat Strain Index Complex! Based on heat balance equation Solve using computer program
  57. 57. Predicted Heat Strain Index Gives maximum allowable exposure times based on o Heat storage o Water loss
  58. 58. 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)
  59. 59. Physiological assessment Temperature Heart rate
  60. 60. Miner’s Core Temperature & Heart Rate Source: OHTA.
  61. 61. Personal Monitor
  62. 62. 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
  63. 63. Hierarchy of Control Prevention Engineering Work Practices PPE
  64. 64. Occupational Health Management Prevention Engineering Work Practices PPE Supervision Maintenance Procedures Auditing Testing Health surveillance Monitoring Information Training Housekeeping
  65. 65. Metabolic Rate Automate Reduce work rate Mechanical aids
  66. 66. Radiant Heat Exchange R = T4 R = Radiant heat in W/m2  = Stefan-Boltzmann constant  = emissivity T = surface temperature in K
  67. 67. Controlling Radiant Heat R = T4 Reduce temperature
  68. 68. Controlling Radiant Heat R = T4 Reduce temperature Minimise size / intensity of source Insulate surfaces Direct / indirect cooling
  69. 69. www.lubisol.com
  70. 70. Controlling Radiant Heat R = T4 Reduce emissivity
  71. 71. Controlling Radiant Heat R = T4 Reduce emissivity Cladding Bright, shiny surfaces e.g. Polished aluminium
  72. 72. www.industrialheating.com
  73. 73. Reflective shielding for radiant heat
  74. 74. Insulate heat sources www.nworrp.org
  75. 75. Increase air movement Be careful as this can increase convective heat gain
  76. 76. Local cooling Introducing pre-cooled air http://mikegigi.com
  77. 77. General ventilation cool air enters at low level through open windows Hot air escapes through roof vent hot process
  78. 78. High humidity Extract humid air Dehumidification Increase air movement
  79. 79. 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
  80. 80. Cooling vests
  81. 81. Management measures Screening & health surveillance Information, instruction, training Supervision Self regulation Provide water
  82. 82. http://www.hse.gov.uk/temperature/thermal/index.htm
  83. 83. http://www.cdc.gov/niosh/topics/heatstress/
  84. 84. http://www.bohs.org/resources/res.aspx/Resource/filename/840/TG12.pdf http://www.bohs.org/resources/res.aspx/Resource/filename/1473/04_TG12_Addendum_to_2nd_Edition.pdf
  85. 85. • ISO 7730 (Thermal comfort) • ISO 7743 (WBGT) • ISO 7933 (Heat stress) Standards
  86. 86. 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)
  87. 87. http://www.slideshare.net/mikeslater occhygiene@btconnect.com http://diamondenv.wordpress.com Twitter @diamondenv Mike Slater

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