Environmental Factors Effects of Temperature Hardianto Iridiastadi Ph

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

Introduction • Cases – Manufacturing plant – Mining – Military – Emergency responders

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Thermoregulation • Human thermoregulation – Temperature outside the range • • • >39. 5 – disabling >42 – fatal 35. 5 – lower acceptable limit <33 – onset of cardiac disturbances < 25 - fatal

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

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

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 100 g/hour; can be up to 1 – 2 kg/h – Loss of 1 l/hr is frequently found

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

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

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

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

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

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

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

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

Measurement • WBGT index – Web bulb globe temperature (WBGT) – WBGT (out) = 0. 7 WB + 0. 2 GT + 0. 1 DB – WBGT (in) = 0. 7 WB + 0. 3 GT

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)

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

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

Recommendation • OSHA monitoring techniques – Pulse > 110 bpm? Reduce work cycle to 1/3 – Oral temperature > 37. 6 o. C? Shorten work period by 1/3 – Body weight loss > 1. 5% during shift? Increase fluid intake – Limit of 38 o. C (deep body temp) for prolonged work (WHO)

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

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)

Recommendation • Preventing dehydration – Plenty of drink before and during work (10 – 15. 6 o. C) – 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)

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

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

Heat Stress Management • OSHA Guidelines – Permissible Heat Exp. TLV Work/Rest Regimen Workload Light Moderate Heavy Continuous 30 26. 7 25 75% work/h 30. 6 28 25. 9 50% work/h 31. 4 29. 4 27. 9 25% work/h 32. 2 31. 1 30