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  1. 1. Management of Work in Hot Environments “Safety in the Heat” Trainers Presentation With thanks to Dr Graham Bates, Dr John Schneider and Dr Veronica Miller © Health Authority - Abu Dhabi 2009
  2. 2. NOTE <ul><li>This presentation is for training OHS professionals and supervisors responsible for employees working in hot conditions. </li></ul><ul><li>It can be adapted and shortened for on-site use and translated into other languages as required. </li></ul><ul><li>It should not be used for commercial purposes and remains the property of HAAD. </li></ul>
  3. 3. Overview <ul><li>What’s the effect of heat stress on work performance </li></ul><ul><li>The importance of hydration </li></ul><ul><li>Heat stress related health issues </li></ul><ul><li>How can we measure heat stress and what can we do to manage it? </li></ul>
  4. 4. Introduction <ul><li>The body is required to get rid of excess heat to maintain a constant internal temperature (37 °C) </li></ul><ul><li>The body ’ s best mechanism for removing any excess heat is through the evaporation of sweat </li></ul>Heat In Heat Out
  5. 5. How does heat alter this? <ul><li>High humidity stops/decreases the evaporation of sweat and therefore no heat is lost </li></ul><ul><li>Muscular strength declines due to increased blood circulation to the skin, resulting in decreased flow to muscles </li></ul><ul><li>Overheating decreases alertness and mental capacity </li></ul>
  6. 6. Blood - the key component <ul><li>Blood has the essential functions of providing oxygen and nutrients to vital organs and working muscles </li></ul><ul><li>However it also carries heat from working muscles and the body’s “core” to the skin so heat can be dissipated </li></ul><ul><li>The blood volume is about 5 L for males and about 4 L for females </li></ul>
  7. 7. So what happens when I work in the heat? <ul><li>Thermal stress results in sweating: </li></ul><ul><ul><li>sweat evaporates producing cooling </li></ul></ul><ul><ul><li>all sweat comes from blood supply initially, so increased sweat results in decreased blood volume </li></ul></ul>
  8. 8. Dehydration: the impact <ul><li>If blood volume decreases you become dehydrated: </li></ul><ul><ul><li>there is less blood available to go to the skin and to ability to dissipate heat is lost </li></ul></ul><ul><ul><li>heart rate increases because of this smaller volume, resulting in excessive fatigue </li></ul></ul><ul><ul><li>blood supply to the gut is reduced resulting in decreased fluid absorption </li></ul></ul><ul><ul><li>less blood is available to supply working muscles </li></ul></ul><ul><ul><li>mental capacity is compromised due to </li></ul></ul><ul><ul><li>decreased blood flow to the brain </li></ul></ul>
  9. 9. Dehydration facts <ul><li>Single biggest cause of heat illness </li></ul><ul><li>“ Thirst” only starts at 2% dehydration of body weight </li></ul><ul><ul><li> Start drinking fluid immediately, don’t wait until thirsty </li></ul></ul><ul><li>Sweat rate can reach up to 1 litre per hour </li></ul><ul><ul><li> Drink small amounts and often (program drinking) </li></ul></ul><ul><li>Typically 40% of workers come to work dehydrated </li></ul><ul><ul><li> Drink plenty of water before coming to work </li></ul></ul><ul><li>Aim for clear to “straw” coloured urine when at work </li></ul><ul><li>Drink so as to urinate frequently ( ~ 4 times a day) </li></ul>
  10. 10. Dehydration: the impact <ul><li>1 to 2% dehydration  6 to 7% reduction in physical work rate </li></ul><ul><li>3 to 4% dehydration  22% to 50% reduction in work rate, for “moderate” and “hot” environments </li></ul><ul><li>Mental performance begins to decrease at 2% dehydration and beyond that decrease proportionally to the level of dehydration </li></ul>
  11. 11. Summary <ul><li>The best way to maintain blood volume and therefore your capacity to stay cool is to prevent dehydration by maintaining fluid intake </li></ul><ul><li>This is the same as ensuring a radiator is topped up with coolant before going on a trip. If the radiator is full the engine won’t overheat, if its only half full its performance will be limited and it will overheat </li></ul>
  12. 12. So what exactly is in sweat? <ul><li>Water </li></ul><ul><li>Sodium (salt) larger amount </li></ul><ul><li>Potassium small amount </li></ul><ul><li>Magnesium, Calcium Virtually none </li></ul>
  13. 13. Fine, but how much fluid do you lose? <ul><li>Average sweat rate ~ 600 mls/hr </li></ul><ul><li>Working for 10 hrs : 6 L lost in a day </li></ul>Hourly Sweat Rate over 6 Hours at 35 ° C and 50% RH
  14. 14. What about salt? <ul><li>Average sodium loss: ~ 40 mmol/L/hr </li></ul><ul><li>Working for 10 hrs at a rate of 600ml/hr = 240mmol </li></ul><ul><li>240 mmol = 5.52 g lost in a day </li></ul><ul><li>About 13 grams of salt which is about 3 teaspoons! </li></ul>Sodium Concentration changes in Arms and Legs over 6 hours (Mean+/- SD)
  15. 15. What’s wrong with caffeine and alcohol? <ul><li>Caffeine and alcohol are diuretics (i.e. they cause increased rate of urination) </li></ul>
  16. 16. Alcohol : an example <ul><li>If you are dehydrated by 3 Kg (3 L): </li></ul>-And you drink 3 litres of full-strength beer -you produce 3.5 kg urine Net LOSS = 0.5 kg -End up 3.5 kg dehydrated -And you drink 3 litres of pure water -you produce 0.0 kg urine. Net GAIN = 3 kg -End up hydrated
  17. 17. Caffeine <ul><li>Coffee (per 250 ml mug) </li></ul><ul><ul><li>Percolated 100-200 mg caffeine </li></ul></ul><ul><ul><li>Instant 70-180 mg caffeine </li></ul></ul><ul><li>Tea (per 250 ml mug) </li></ul><ul><ul><li>1 minute brew 15-55 mg caffeine </li></ul></ul><ul><ul><li>5 minute brew 30-80 mg caffeine </li></ul></ul>
  18. 18. Caffeine (cont.) <ul><li>Caffeinated drinks (per 375 ml can) </li></ul><ul><ul><li>Coke 75 mg caffeine </li></ul></ul><ul><ul><li>Pepsi 60 mg caffeine </li></ul></ul><ul><li>Energy drinks (per 250ml can) </li></ul><ul><ul><li>Red Bull 80 mg caffeine </li></ul></ul><ul><ul><li>V 78 mg caffeine </li></ul></ul>
  19. 19. What you can do to limit these effects <ul><li>Drink tea in preference to coffee </li></ul><ul><li>Drink weaker coffee or tea </li></ul><ul><li>Reduce or eliminate intake of cola and energy drinks </li></ul><ul><li>Drink a cup of water every time you drink a cup of tea or coffee </li></ul><ul><li>When drinking alcohol make sure you are hydrated when you start </li></ul>
  20. 20. Can hydration status be tested? <ul><li>Simple test ; Urine Specific Gravity using a refractometer </li></ul><ul><ul><li>Takes less than one minute </li></ul></ul><ul><ul><li>Measures concentration of urine compared to water </li></ul></ul>
  21. 21. Specific Gravity : what it means <ul><li>1.000  1.010 Excellent </li></ul><ul><li>1.010  1.015 Okay </li></ul><ul><li>1.015  1.020 Need fluid </li></ul><ul><li>1.020  1.025 Hypo-hydrated </li></ul><ul><li>1.025  1.030 Dehydrated </li></ul>
  22. 22. So what are the health problems associated with heat stress? <ul><li>Heat Stroke </li></ul><ul><ul><li>body ’ s system of temperature regulation fails </li></ul></ul><ul><ul><li>body temperature rises to critical levels  deep body temp. exceeds 40°C </li></ul></ul><ul><ul><li>primary signs: confusion, irrational behaviour, loss of consciousness, convulsions, lack of sweating, hot dry skin </li></ul></ul>
  23. 23. <ul><li>Heat stroke first aid </li></ul><ul><ul><li>call medical attention immediately </li></ul></ul><ul><ul><li>move person to shade </li></ul></ul><ul><ul><li>remove clothing and wet skin </li></ul></ul><ul><ul><li>increase local air velocity </li></ul></ul><ul><ul><li>increase fluid intake if possible </li></ul></ul><ul><ul><li>can lead to permanent brain damage and death </li></ul></ul>
  24. 24. <ul><li>Heat Exhaustion </li></ul><ul><ul><li>symptoms resemble heat stroke and include headache, nausea, weakness, thirst and giddiness </li></ul></ul><ul><ul><li>caused by loss of large amounts of fluids as sweat </li></ul></ul><ul><ul><li>skin is clammy and moist </li></ul></ul><ul><ul><li>complexion is red with rapid pulse </li></ul></ul><ul><ul><li>body temperature is normal or slightly elevated </li></ul></ul><ul><li>Heat exhaustion first aid </li></ul><ul><ul><li>rest in cool place </li></ul></ul><ul><ul><li>drink plenty of fluids </li></ul></ul><ul><ul><li>severe cases could take one or two days to recover </li></ul></ul><ul><ul><li>no known permanent side effects </li></ul></ul>
  25. 25. <ul><li>Heat Cramps </li></ul><ul><ul><li>painful muscle spasm that occurs when sweating profusely in heat </li></ul></ul><ul><ul><li>electrolyte imbalance caused by sweating </li></ul></ul><ul><ul><li>water may be drunk but person must </li></ul></ul><ul><ul><li>replace lost electrolytes </li></ul></ul><ul><li>Avoidance of heat cramps </li></ul><ul><ul><li>thirst cannot be used as a guide for the </li></ul></ul><ul><ul><li>need to drink fluid </li></ul></ul><ul><ul><li>water must be taken every 15-20 min in hot environments </li></ul></ul><ul><ul><li>drink electrolyte replacement fluids </li></ul></ul><ul><ul><li>muscles being used are most susceptible </li></ul></ul>
  26. 26. <ul><li>Heat Collapse (fainting) </li></ul><ul><ul><li>workers not accustomed to hot environments who stand upright and immobile for long periods of time </li></ul></ul><ul><ul><li>blood pools </li></ul></ul><ul><ul><li>inadequate venous return resulting in decreased blood pumped to brain </li></ul></ul><ul><ul><li>prevented by keeping workers moving and an acclimatisation program </li></ul></ul>
  27. 27. <ul><li>Heat Rash (prickly heat) </li></ul><ul><ul><li>occurs most commonly in hot, humid environments </li></ul></ul><ul><ul><li>sweat is not easily removed from skin </li></ul></ul><ul><ul><li>sweat ducts become blocked, causing rash </li></ul></ul><ul><ul><li>prevent by cool breaks and regular bathing and drying of skin </li></ul></ul><ul><li>Heat Fatigue </li></ul><ul><ul><li>temporary state of mental or psychological strain resulting from prolonged heat exposure </li></ul></ul><ul><ul><li>decline in task performance, coordination, alertness </li></ul></ul><ul><ul><li>reduced by heat acclimatisation </li></ul></ul>
  28. 28. Long term health effects of heat stress <ul><li>Kidney stones is the most common </li></ul><ul><li>Cancer of the bladder has recently been reported </li></ul><ul><li>Possibly other effects in certain individuals from too much sugar i.e. when sweat replaced with full strength soft drinks and caffeinated drinks </li></ul>
  29. 29. What about safety issues? <ul><li>Heat promotes accidents: </li></ul><ul><ul><li>slipperiness of sweaty palms </li></ul></ul><ul><ul><li>dizziness </li></ul></ul><ul><ul><li>fogging of safety glasses </li></ul></ul><ul><ul><li>hot surfaces/steam  burns </li></ul></ul><ul><ul><li>lower mental alertness and individual physical performance </li></ul></ul><ul><ul><li>physical discomfort promotes irritability, anger and other emotions </li></ul></ul>
  30. 30. Acclimatisation <ul><li>Within limits, the human body adapts to working in heat </li></ul><ul><li>In one medically-controlled study: </li></ul><ul><ul><li>Blood volume increased by up to 30% (ave. 21%) </li></ul></ul><ul><ul><li>Sweated more profusely, up by 50% </li></ul></ul><ul><ul><li>Sweat started 15% earlier </li></ul></ul><ul><ul><li>Sodium (salt) concentration in sweat down by 29% </li></ul></ul><ul><ul><li>Heart rate fell from 153 to 127 beats per min </li></ul></ul><ul><ul><li>Core temperature fell from 38.80 °C to 38.10 °C </li></ul></ul>
  31. 31. The 3 phases of acclimatisation <ul><li>Initial phase - occurs during early consecutive days of exposure to heat - usually 33% of optimum by day 4 </li></ul><ul><li>Intermediate phase - when cardiovascular stability has been assured and surface and internal body temperatures are lowered. Usually 44% optimum by day 8 </li></ul><ul><li>Third phase - decrease in sweat and urine composition, and other compensations to conserve body fluids and restore electrolyte balances. </li></ul><ul><ul><li>Day 10 - 65% of optimum </li></ul></ul><ul><ul><li>Day 18 - 93% of optimum </li></ul></ul><ul><ul><li>Day 21 - 99% of optimum </li></ul></ul><ul><li>Requires elevated metabolic rate for over 2 hours/day </li></ul>
  32. 32. Acclimatisation, how long does it take to gain and lose?
  33. 33. Acclimatisation benefits <ul><li>More finely tuned sweating reflexes with increased sweat production rate at lower electrolyte concentrations </li></ul><ul><li>Lower rectal and skin temperatures than at the beginning of exposure </li></ul><ul><li>More stable and better regulated blood pressure with lower pulse rates </li></ul><ul><li>Improved productivity and safety </li></ul>
  34. 34. Other benefits <ul><li>Thermal Comfort – Improved </li></ul><ul><li>Exercise Performance – Improved </li></ul><ul><li>Core Temperature – Reduced </li></ul><ul><li>Sweating – Earlier & Greater </li></ul><ul><li>Skin Blood Flow – Earlier </li></ul><ul><li>Body Heat Production – Lower </li></ul><ul><li>Heart Rate – Lowered </li></ul><ul><li>Thirst – Improved </li></ul><ul><li>Salt Losses (sweat & urine) – Reduced </li></ul><ul><li>Organ Protection – Improved </li></ul>
  35. 35. Air-conditioning <ul><li>Alternating hot and cold conditions: </li></ul><ul><ul><li>Does not cause “colds” </li></ul></ul><ul><ul><li>Can result in “chill” to kidney area: thermal “shock” </li></ul></ul><ul><ul><li>Will not cause any permanent problems </li></ul></ul><ul><ul><li>Do not set air-conditioning temperature too low </li></ul></ul><ul><ul><li>Aim for about 25 ° C inside </li></ul></ul>
  36. 36. What factors will affect our ability to remove excess heat? <ul><li>Physical factors </li></ul><ul><ul><li>age </li></ul></ul><ul><ul><li>weight </li></ul></ul><ul><ul><li>physical fitness </li></ul></ul><ul><ul><li>acclimatisation </li></ul></ul><ul><ul><li>metabolism </li></ul></ul><ul><ul><li>use of alcohol or drugs </li></ul></ul><ul><ul><li>hypertension </li></ul></ul><ul><ul><li>general health </li></ul></ul>
  37. 37. Why does my weight matter? <ul><li>The best measure of your weight “status” is Body Mass Index or BMI </li></ul><ul><li>BMI= weight (kg)/ height (m) ² </li></ul><ul><li>A “guide” to risk of chronic health problems, life expectancy, and likelihood of poor </li></ul><ul><li>quality of life in old age </li></ul><ul><li>BMI : < 19 UNDERWEIGHT 20 - 25 ACCEPTABLE 26 - 30 OVERWEIGHT > 31 OBESE </li></ul>
  38. 38. BMI – the impact <ul><li>7690 workers injury reports examined </li></ul><ul><li>29% where injured over 3 yrs </li></ul><ul><li>85% of these were overweight (25-30) or obese (>30) </li></ul><ul><li>28% were overweight and 64% obese </li></ul><ul><li>Those with BMI >40 were twice as likely to sustain an injury </li></ul><ul><li>(am j epidemiol 2007 pollock et al) </li></ul>
  39. 39. The importance of physical fitness <ul><li>Heat stress places additional cardiovascular strain, hence superior aerobic capacity is a big advantage </li></ul><ul><li>Workers who are selected for hot jobs that are in good general health and physical condition have less chance of getting heat stroke and other heat related illnesses </li></ul><ul><li>Short term and minor illnesses should </li></ul><ul><li>also be considered - flu, diarrhoea, </li></ul><ul><li>vomiting, hangover </li></ul><ul><li>Workers on medication should seek </li></ul><ul><li>medical clearance </li></ul>
  40. 40. What else can you do outside the workplace? <ul><li>Drink water outside of work not just caffeine (tea, coffee, Coke) or alcohol (beer, spirits, wine) </li></ul><ul><li>Good diet </li></ul><ul><li>Good quality sleep </li></ul>
  41. 41. So what factors are we talking about in relation to heat stress? <ul><li>Wet bulb temperature is the most important and is measured using a wet bulb thermometer </li></ul><ul><li>WB is the temperature at which water evaporates into the air </li></ul><ul><li>Significant when compared to skin temperature </li></ul><ul><li>because of the affect it has how much of an </li></ul><ul><li>individuals sweat evaporates </li></ul><ul><li>Dry bulb temperature (ambient temp.) is not as </li></ul><ul><li>important and is measured using a regular </li></ul><ul><li>thermometer </li></ul>Air Temperature
  42. 42. Radiant Heat <ul><li>Heat energy transmitted by electromagnetic waves in contrast to heat transmitted by conduction or convection </li></ul><ul><li>Measured using a “globe thermometer” [a 150 mm diameter hollow copper ball (painted black) with a standard thermometer in it] </li></ul><ul><li>Significant for deep mines, workers on or near diesel units and workers in the sun or in smelters </li></ul>
  43. 43. Relative Humidity <ul><li>Relative Humidity is a percentage of the actual amount of moisture in the air, compared to the maximum moisture that can be taken up by the air at that temperature </li></ul><ul><li>50% or more of sweat can drop off skin </li></ul><ul><li>Only sweat which evaporates off skin </li></ul><ul><li>produces cooling </li></ul><ul><li>Sweat which drops off just adds to </li></ul><ul><li>dehydration load </li></ul><ul><li>Dry air means more evaporates and </li></ul><ul><li>less drips off  keep air dry (low humidity) </li></ul>
  44. 44. Wind Speed <ul><li>The higher the wind speed the better </li></ul><ul><li>Wind speed increases evaporation of sweat </li></ul><ul><li>Use air-movers where possible </li></ul><ul><li>Ensure ventilation systems are working effectively at all times </li></ul><ul><li>Report any leakage or short-circuiting </li></ul>
  45. 45. Personal Protection Equipment <ul><li>PPE is necessary to protect from hazards </li></ul><ul><li>PPE “insulates” the body & adds to heat stress </li></ul><ul><li>Use only the PPE required </li></ul><ul><li>Wear T-shirts/short sleeves when safe and appropriate </li></ul><ul><li>Ensure long sleeved shirts are “baggy” [loose sleeves at elbows] </li></ul><ul><li>Use shirts & trousers in preference to overalls </li></ul><ul><li>Spraying water over you is effective in cooling </li></ul><ul><li>Carry plenty of water with you on the job and make sure there is close access to cool water </li></ul>
  46. 46. Visitors <ul><li>We also have a “Duty of Care” towards visitors </li></ul><ul><li>Visitors need to be told of the hazards they need to be aware of during their visit, including hazards from heat, and what to do if the unexpected happens </li></ul><ul><li>If applicable, visitors going underground/out in the field should complete a self-assessed medical questionnaire </li></ul>
  47. 47. How can we measure the workplace environment? <ul><li>Depends on: </li></ul><ul><li>- how hot it is where you are working  wet bulb temp./humidity, air temp., wind speed, radiant heat </li></ul><ul><li>- how hard you are working  the harder you work the more heat you will generate </li></ul><ul><li>- your clothes and PPE  these reduce evaporation of sweat </li></ul>
  48. 48. The equation: Heat generated by worker + heat from the environment Cooling due to evaporation & other means
  49. 49. Thermal Work Limit <ul><li>The work rate that acclimatised workers can safely maintain in a particular environment is called the </li></ul><ul><li>Thermal Work Limit </li></ul>
  50. 50. So what does it mean? <ul><li>A HIGH TWL means better working conditions, A LOW TWL means poorer working conditions </li></ul><ul><li>TWL measures environmental conditions </li></ul><ul><li>TWL is the metabolic limit measured in Watts/m 2 that can be tolerated before heat storage occurs (hyperthermia) </li></ul>
  51. 51. TWL (cont.) <ul><li>Measures all essential environmental parameters </li></ul><ul><li>Considers clothing </li></ul><ul><li>Can be used for work rest cycling </li></ul><ul><li>Can be used for calculating maximal duration in a measured environment </li></ul><ul><li>Has been scientifically validated </li></ul>
  52. 52. Calculating TWL <ul><li>Can be calculated using instruments (DB, WB, Rad., WS) </li></ul><ul><li>i.e. the Heat Stress Meter </li></ul><ul><li>Use HAAD Desktop calculator for data input and calculation of TWL see </li></ul>
  53. 53. TWL cut-offs <ul><li>Field studies have suggested the following guidelines: </li></ul><ul><li>< 115 watts/m 2 : Withdrawal limit for self-paced, self-supervised workers as below this level even light work is not continuously sustainable even for fully acclimatised workers. Formal “permitting system” with management approval required to work. </li></ul><ul><li>115 - 140 watts/m 2 : “Buffer zone” - work is restricted. A system of written “corrective action requests” is required to ensure rotation of workers and correction of environmental engineering defects, i.e can improvements be made. </li></ul><ul><li>140 - 220 watts/m 2 : Work restricted to acclimatised workers. The acclimatisation period lasts for the first 7 days back at work after an absence of >14 days. </li></ul><ul><li>> 220 watts/m 2 : Unrestricted work. </li></ul>
  54. 54. Conclusions <ul><li>Hypo/De-hydration is the major factor causing heat illness </li></ul><ul><li>Fluid replacement is essential </li></ul><ul><li>Sodium is essential to replace </li></ul><ul><li>Urine SG is a good indicator of hydration status </li></ul><ul><li>Acclimatisation for workers should be considered </li></ul><ul><li>TWL is a valid index to assess the environment </li></ul>
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