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Thermal Stress

Thermal Stress. Industrial Hygiene IENG 341 Dr. Carter J. Kerk Industrial Engineering Department SD School of Mines Spring 2009. Assignment. Read Plog, Chapter 12. Outline – Thermal Stress. Temperature Extremes Heat Stress Cold Stress Related Illnesses

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Thermal Stress

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  1. Thermal Stress Industrial Hygiene IENG 341 Dr. Carter J. Kerk Industrial Engineering Department SD School of Mines Spring 2009

  2. Assignment • Read Plog, Chapter 12

  3. Outline – Thermal Stress • Temperature Extremes • Heat Stress • Cold Stress • Related Illnesses • Identification, Evaluation, Control

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

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

  6. 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

  7. Stable ± 1° 37 C 98.6 F Body Temperature 16 C / 60 F 54 C / 130 F Temperature of Dry Still Air

  8. 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

  9. 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

  10. 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

  11. 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

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

  13. Supplemental Reference • Nims DK, Basics of Industrial Hygiene, John Wiley & Sons, New York, NY, 1999.

  14. Assignment • Read Plog, Chapter 12

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