SIMPLE MEASUREMENT OF THE WBGT INDEX

The physiological effects of heat stress have been researched extensively by the South African mining industry where deep mining necessitates heavy physical work being undertaken in hot and humid conditions.

Heat stress is caused by a combination of high dry bulb temperature, radiant heat and high humidity. The latter limits the body’s ability to cool itself and is indicated by the wet bulb temperature. In extreme cases of heat stress the body generates heat at a greater rate than the heat can be dissipated and symptoms of heat stroke follow.

The effect of wet bulb temperature is highly significant and the experience of the mining industry shows that not only does the accident frequency increase with the increase of wet bulb temperature above 27°C, but also that heat stroke fatalities can be expected at wet bulbs above 28°C and dramatically at wet bulbs higher than 34°C.

According to Rob Goldblatt of Runrite Electronics, the manufacturers of Tempstress Heat Stress Monitor, although such hostile conditions do not commonly occur in general industry above ground, the effects of heat stress should, nevertheless, be taken into account. Worker health and comfort can be adversely affected by high WBGT and productivity can fall.

The OHS Act determines that the environment should be assessed in terms of the WBGT index, which is a function of wet bulb, globe and dry bulb temperature. The Tempstress was designed in South Africa and calculates this index automatically. With over 600 units sold locally, it remains the most cost effective solution to heat stress measurement.

The Tempstress kit is supplied in a sturdy foam lined executive case and comprises all the components necessary to make a WBGT measurement. Included in the kit are two check-plugs which are used to verify calibration before use. Operation is straightforward and with the instrument mounted on the tripod either wet bulb temperature, WBGT, or globe temperature can be displayed at the touch of a switch.

The Tempstress has a digital display and three audible modes, ‘correct function bleep’, ‘battery low alarm’ and ‘WBGT high alarm’. The WBGT high alarm is normally factory set at 30°C but can be changed to suit customer requirements. The OHS Act stipulates that where the time-weighted average WGBT index exceeds 30 when determined over a period of one hour in the environment in which an employee works, appropriate action must be taken by the employer in accordance with the steps outlined in the Act.