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 Students will demonstrate engineering methodology during these lab activities

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

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

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.

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

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

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

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

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

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

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