Heat Monitoring

An introduction to monitoring heat stress

Why measure heat stress
Workers exposed to hot working environments can be susceptible to heat stress, when the core temperature of the body rises to dangerous or hazardous levels. This can result in psychological symptoms like heat cramps, nausea, palpitations, stroke and even ultimately death. The overall estimation of heat stress levels on the body can be measured by using the wet bulb globe temperature index (WBGT). The measurements obtained from a suitable monitor such as the Casella Microtherm HSM are compared to reference values (as defined by the standards and appropriate "work rest" regimes) can then be adopted in the workplace or more detailed medical analyses undertaken.

Go straight to suitable products >
3 temperature sensors on the Microtherm HSM probe
What is the WBGT index
 This combines the measurements of three parameters from precision thermometers; the natural wet bulb temperature (tnw), the globe temperature (tg) and the ambient air temperature (ta). These three indexes are applied to the following formulae for both indoor and outdoor environments:

WBGT (indoor) = 0.7 tnw + 0.3 tg

WBGT (outdoor) = 0.7 tnw + 0.2 tg + 0.1 ta

As well as the time history values being taken at regular intervals the Casella Heat stress instruments can calculate the time weighted average (TWA) WBGT index and display it on the screen.
 
screen display from Microtherm HSM showing the calculated indoor value of WBGT
Applications
Typical applications where this can be a hazard include; power stations, foundries, steel works, bakeries, glass manufacturing and other similar energetic professions where excessive body heat buildup could be dangerous. The effect of the type of clothing worn by the worker can obviously be a contributing factor and these can be taken into account to arrive at a recommended "safe" WBGT working value based on the percentage of actual work time during the day. The WinHSM software included with the Casella WBGT monitor is able to take all of these factors into account when results are downloaded to the computer and produces a result according to the relevant OSHA and ISO recommendations. The Casella Indoor air quality monitor can also measure the WBGT index and can correlate these results with NOx and SOx sensors for a more thorough understanding of the situation.


a typical hot and hazardous environment
this page last updated : Monday January 14, 2008