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WBGT Lab

WBGT Lab. Auburn University. Objectives. Students will demonstrate understanding of heat effects on human performance related to occupational tasks by answering case study questions Students will demonstrate familiarity with the WBGT by taking and recording sample data with the device

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WBGT Lab

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  1. WBGT Lab Auburn University

  2. Objectives • Students will demonstrate understanding of heat effects on human performance related to occupational tasks by answering case study questions • Students will demonstrate familiarity with the WBGT by taking and recording sample data with the device • Students will demonstrate engineering methodology during these lab activities

  3. Resources • Human Factors in Engineering and Design, Sanders and McCormick, 7th edition, Ch 17 • Safety and Health for Engineers, Brauer, 2nd edition, CH 18 • Engineering Physiology,Kroemer, Kroemer, Kroemer-Elbert, 3rd edition, CH 9

  4. Introduction • Humans have a limited capacity to tolerate extremes in temperature. • limited internal response to change blood flow • conserve or lose heat • can shiver or sweat • require clothing, shelters, conditioned air to tolerate other than most moderate environments • Generating excessive heat is more of a problem in most environments

  5. What is Cold? • Answer: absence of heat. • Cold objects absorb heat from warm ones. • A human body will absorb heat from a warmer environment. • A human body will lose heat to a colder environment.

  6. Heat Exchange Equation • Body Heat Stored: • BH(stored)=(M-W)+/-(R)+/-(C)-E • Where: • M=metabolism gain • W=work performed • R=radiative heat gain or loss • C=Convective gain or loss • E=evaporative loss

  7. Relevance for IEs • The physics of heat storage remain in effect at all times • Environmental conditions can significantly effect the ability of the individual to maintain body heat in the ideal range • homeostasis • Work performance can suffer if the individual’s heat equation is out of balance • Medical emergencies can result if significant imbalance exists

  8. The Problem • To identify an index and measurement system that predicts environmental effects of human performance and safety • Must be relatively: • Portable • Accurate • Simple • Quick

  9. A Solution • Wet Bulb Globe Temperature (WBGT) Index • Weighted average of: • Natural wet bulb Temp (NWB) • Globe Temp (GT) • Dry bulb Temp (DB) • Formulas for sunny or non-sunny conditions

  10. Plusses of WBGT • Plusses: • Air velocity inferred and not measured directly simplifies data collection • Takes into account the previously mentioned variables: NWB, GT, DB Temps • Formulas for solar load/no solar load conditions • Can calculate average for exposure to different environments in 8 hour day

  11. Plusses and Minuses of WBGT • Negatives: • May not be adequate in accounting for air velocity • Similar scores (weighted averages) may have differing effects on human performance based on the ratios of the variables • Example: high humidity and low air velocity may be underestimated relative to effect on human performance yet may give a similar score as a more benign condition

  12. Other for determining temperature stress • To determine work tolerance need to know: • Metabolic activity in kcal/hour • TLVs or RAL/RELs. • Clothing/PPE status-assumes light summer clothing such as long sleeve shits and pants • Whether worker is acclimatized or not • at least 10 days-3 weeks progressive exposure

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