Thermal Stress

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Thermal Stress

• Industrial Hygiene
• IENG 341
• Carter J. Kerk
• Industrial Engineering Department
• SD School of Mines
• Spring 2008

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Assignment

• Read Nims, Chapter 11
• Read Section 11-2, but we will not cover in
  lecture
• Critical Thinking Questions
• 1 7
• 8 Tell what is wrong with this question.
• Due?

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Outline Thermal Stress

• Temperature Extremes
• Heat-Related Illnesses
• Cold Stress

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Introduction

• Very high and very low temperatures pose hazards
  to workers
• Extreme cases can be fatal
• Several identification, evaluation, and control
  methods are available

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Thermal Homeostasis

• The body is constantly attempting to maintain a
  favorable and uniform internal temperature,
  despite fluctuations in the environment

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Body Thermal Regulation is Analogous to an HVAC
System
Heat
Circulation Sweating Hormones Shivering
Body Temperature
Temperature Set Point
Comparator
Sensors
Comparator Hypothalamus Sensors Skin, Organs
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Stable 1
98.6 F
37 C
Body Temperature
16 C / 60 F
54 C / 130 F
Temperature of Dry Still Air
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The Human Engine Energy Balance

• Homeostasis over time the body maintains balance
  between energy input output
• Compare the metabolic system to an internal
  combustion engine
• Systems involved digestive, respiratory,
  circulatory, muscle systems
• Inputs oxygen, food
• Digestive system receives and processes the food
• Intestines Liver pass nutrients into blood
  stream for delivery to muscle sites
• Muscle sites nutrients join with oxygen for
  metabolism

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Human Engine Continued

• Products of metabolism external energy (work),
  internal energy (maintain body temp)
• By-products of metabolism CO2, H2O, Heat
• Some heat is transported close to the skin and
  lost via perspiration convective loss
• Vasoconstriction vasodilation
• Remainder of CO2, H2O, and heat is transported
  back to alveolar interface and expired by the
  respiratory system

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Energy Balance Equation

• M S R C K W E 0
• M, metabolic rate
• S, heat storage rate
• R, radiant heat exchange rate
• C, convective heat exchange rate
• K, conductive heat exchange rate
• W, mechanical work rate
• E, evaporative cooling exchange rate
• Units watts (W), or joules/sec (J/s)
• 1 W 1 J/s

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In Heat Stress Situation

• Limit radiant heat gain (sun, blast furnace, open
  flames, etc.)
• Provide shade or a barrier
• Clothing can be a barrier but interferes with
  evaporation
• Wear cool packs near skin
• Limit work rate
• Restrict work time

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Extreme Cold Stress

• Keep skin covered and protected
• Insulative clothing layers are necessary
• Take extra care to protect fingers, feet, face,
  and neck

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Assignment

• Read Nims, Chapter 11
• Read Section 11-2, but we will not cover in
  lecture
• Critical Thinking Questions
• 1 7
• 8 Tell what is wrong with this question.
• Due?