Understanding the Impact of Environmental Factors on Temperature

1. Environmental Factors Effects of Temperature Hardianto Iridiastadi, Ph.D.

2. Introduction • Cases • Manufacturing plant • Mining • Military • Emergency responders

3. Introduction • Comfortable environment • Temperature • Humidity • Air distribution • Also affected by • Seasons of year • Dry and wet bulb temperature • Cultural practices and habits

4. Introduction • Comfortable environment • Chart for certain populations • E.g., ASHRAE Handbook • Increased heat • Environment • Physical activities

5. Heat Transfer • How it occurs • Object with higher temperature to that with lower temperature • Mechanisms • Conduction (typically not a significant factor) • Convection • Radiation

6. Heat Exchange • Sources of heat • Metabolic (internally generated) • Environmental (externally imposed) • Net heat exchange H = M + R + C – E H = heat storage M = metabolic heat gain R = radiant/infrared heat C = convection E = evaporative

7. Problems with Heat • Heat stress • Common across industries • Total heat imposed on the body • Heat strain • Physiological responses to the body • Reflects the degree of heat stress • Varies from discomfort to disorders

8. Problems with Heat • Influencing factors • Heat stress intensity • Age • Physical fitness • Degree of aclimatization • Dehydration level • Alcohol intake • Obesity

9. Problems with Heat • Heat disorders • Can be distinguished clinically • Rangin from heat syncope (fainting) to complex heatstroke

10. Problems with Heat • Effects on the workers • Faint while standing erect • Painful muscle spasms (during or after work) • Impaired performance • Mental • Vigilance • Sensorimotor • Reduced capacity • Poor behavior

11. Problems with Heat • Central nervous system • Hypothalamus of the brain acts as a control/thermostat • Initiates to cool/heat the body, if temperature difference exists

12. Problems with Heat • Heat illnesses • Heat stroke • Thermoregulation fails • Core temperature exceeds 41oC • Fatal if untreated • One may collapse and disoriented • Skin is hot, red, and dry • Active cooling is needed

13. Introduction • Heat illnesses • Heat exhaustion • Combined strain (thermoregulatory and cardiovascular) • One feels weak and un-coordinated • Shallow breath • Rapid, weak pulse • Treatment via removing from the heat, removal of clothing, and fanning

14. Introduction • Heat illnesses • Heat syncope • Fainting due to inadequate venous return • Common for unacclimatized person • Need to lie down • Heat hyperventilation • Excessive loss of carbon dioxide • Can occur while wearing protective clothing

15. Introduction • Heat illnesses • Prickly heat • Fine, superficial skin rash • Due to excessive sweating • Often occurs on areas of skin covered by clothing or protective equipment

16. Thermoregulation • Human thermoregulation • Ability to tolerate heat • Balance between metabolic heat produced and heat loss • Objective to maintain core temp. at 36 – 37oC • Stability needed for most biochemical reactions

17. Thermoregulation • Human thermoregulation • Temperature outside the range • >39.5 – disabling • >42 – fatal • 35.5 – lower acceptable limit • <33 – onset of cardiac disturbances • < 25 - fatal

18. Human Thermoregulation • Human thermoregulation • Heat gained • Metabolic energy production • Radiation • Convection • Conduction (minimal) • Heat loss • Evaporation, Radiation, Convection • Balance between the two

19. Human Thermoregulation • Human thermoregulation • Evaporation • Sweat production and evaporation as means to loose heat to the environment • The importance of maintaining the balance via a variety of methods

20. Sweating • What it is… • Sweat glands stimulated by the nerves • A dilute solution of various electrolytes (sodium, potassium, and chloride); mainly salt (sodium chloride) • Potential loss of 500 g/sq.m • Loss of 100g/hour; can be up to 1 – 2 kg/h • Loss of 1 l/hr is frequently found

21. Sweating • What it is • Sweat cools the body (only if evaporates) • Less efficient in humid environment • Result in dehydration and loosing salt • Affected by air humidity and movement

22. Sweating • Sweat and dehydration • 1 liter fluid loss ~ 1 kg drop in body weight • Workers can be weighed before and after • Dehydration increases risk of heat exhaustion

23. Sweating • Risk of dehydration • 1% of body weight (max) – use this as maximum of work period • 2% loss – performance decrement and unpleasent • 4% loss – maximum allowed • 4 liter sweat (max) / 8 hr (WHO) • 6% loss – threat to health

24. Measurement • Dry bulb temperature • Common thermometers • Wet bulb temperature • Thermometer with wet cloth “sock” • Globe temperature • Measure the effects of radiant heat

25. Measurement • Climatic factors • Humidity? • Relative humidity? • Water vapor pressure? • Dew point?

26. Measurement • Five key variables • Relative humidity (rh) • Dew point temperature (tdp) • Dry bulb temperature (DBT) • Wet bulb temperature (WBT) • Vapor pressure (pa) • Psychrometric chart

27. Measurement • Relative humidity • % water vapor pressure (against saturated pressure) • Air movement • Affects evaporation

28. Measurement • Heat stress indices • Dry bulb temperature • Wet bulb temperature • Effective temperature • WBGT index

29. Measurement • WBGT index • Web bulb globe temperature (WBGT) • WBGT (out) = 0.7WB + 0.2GT + 0.1DB • WBGT (in) = 0.7WB + 0.3 GT

30. Measurement • Heat stress monitor • Place where workers do the job; but with no workers • Measure once/hr • Sampling, if workers move around • Also measure outdoor temp (wet and dry)

31. Factors to Consider • Worker • Tolerance • Aerobic capacity • Age, gender, body fat • Acclimatization • Max 1 l/h for un-acclimatized person • Less blood flow need, more blood volume, less salt concentration, and max 2 l/h for acclimatized person

32. Factors to Consider • Environment • Humidity (RH), heat, shade • Wind speed, etc. • Task requirements • Work rate, rest schedule, protective clothing

33. Recommendation • OSHA monitoring techniques • Pulse > 110 bpm? Reduce work cycle to 1/3 • Oral temperature > 37.6oC? Shorten work period by 1/3 • Body weight loss > 1.5% during shift? Increase fluid intake • Limit of 38oC (deep body temp) for prolonged work (WHO)

34. Recommendation • General control methods • Acclimatization • Fluid replacement • Engineering controls • Administrative controls and work practices • Worker monitoring program

35. Recommendation • Acclimatization • Lower heart rate • Lower body temperature • Higher sweat rate • More dilute (less salt) sweat • 2 hrs/day (for a week or two); incrase gradually • Acclimatization lost in days (traces in 2 – 3 months)

36. Recommendation • Preventing dehydration • Plenty of drink before and during work (10 – 15.6oC) • One cup of fluid every 20 min (OSHA) • Avoid caffeine (& drugs) while working • Provide fluid-rich foods (soup, yoghurt, etc.) • Provide only water (no energy drink) • Juice and milk absorbed slower • Salt provision in a separate diet (enough)

37. Recommendation • Engineering controls • General ventilations • Air conditioning • Air cooling • Convection (fans) • Shielding • Heat conduction

38. Heat Stress Management • Basic steps • Use dehumidifiers, increase air movement • Remove heavy clothing • Reduce work rate • Frequent rest pauses • Job rotation • Outdoor work during cooler times • 2-week of acclimatization • Rest, water, shade, cool spots

39. Heat Stress Management • OSHA Guidelines – Permissible Heat Exp. TLV