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There are numerous occupational and leisure tasks for which the participants are at risk of heat stress related illness. Heat stress illness effects can be either acute, such as heat stroke, heat exhaustion, heat cramps, fainting, and decline of performance; or chronic, such as loss of ability to tolerate heat, hypertension, heart muscle damage, reduced libido and impotence. Existing practices for protection against heat stress are limited to awareness education of antagonistic conditions. Persistent monitoring of individuals is not an existing practice due to a variety of factors, including drawbacks to the sensor devices and lack of quantitative definition of heat stress limits.This project presents a Bondgraph model to illustrate the body-ambient heat exchange and how it would be measured using a heat flux transducer. Individual contributions to body heat are shown as r-elements. A measurement device of a heat flux transducer is shown as a transformer element. The equation layer of the model can be tailored for various operating conditions, using either derived or empirical formulas to describe heat transfer. The model shows the same various components of body ambient heat exchange as are found in most occupation educational literature. Bondgraph figures further demonstrate causality and direction of power flow. Not fully quantified in the literature uncovered in research are how the body thermoregulatory functions begin to break downThis data suggest that given a sound understanding of the heat transfer mechanisms operating with the human body during high risk tasks and environments, a heat flux transducer should provide a leading indicator of heat stress illness for any variety of tasks.

Introduction

There are numerous occupational and leisure tasks for which the participants are at risk of heat stress related illness. Existing practices for protection against heat stress are limited to education of antagonistic conditions.

Education and self monitoring has the drawbacks in that any person tasked in making a qualitative judgment has motivating factors against protecting themselves. Methods for persistent monitoring exist but have not been adopted by industry for several factors. Measurement of body core temperature is impractical for almost all occupations. Measurement of skin temperature is not dependable as it is not a leading indicator of heat stress illness.

The bondgraph model provides a complete system view of the contributors to heat stress, and the equation layer of the model can be tailored for various operating conditions, using either derived or empirical formulas to describe heat transfer. This paper describes a model tool such that a heat flux transducer can provide a leading indicator of heat stress illness for a variety of tasks.

Model

A Bondgraph model is a graphical technique to describe energy flow in and amongst physical systems. Presented below is a Bondgraph model to illustrate the body-ambient heat exchange and how it would be measured using a heat flux transducer

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Source:  OpenStax, Body ambient bondgraph model using heat flux transducer. OpenStax CNX. May 15, 2008 Download for free at http://cnx.org/content/col10530/1.1
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