Page 211 - Safety Memo

When the heart rate measurement of a worker exceeds 110 beats per minute, it will be necessary to
have the worker take immediate action to reduce this high heart rate. This action may take the form
of either removal from the hot environment to a cooler location, beginning a work/rest regimen,
wetting down of the over garments, a change in the type and location of work, or whatever else it
requires to reduce the heart rate.

Worker monitoring should continue until a work/rest cycle is established which controls work weight
loss and heart rate measurements to an acceptable level.

METHOD OF TEMPERATURE MEASUREMENT

Since measurement of deep body temperature is impractical for monitoring a worker’s heat load on a
jobsite, the temperature measurement required must be that of the environmental factors that most nearly
correlate with deep body temperature and other physiological responses to heat. At the present time, the
Wet Bulb Globe Temperature Index (WBGT) is the simplest and most suitable technique to measure
these environmental factors. The determination of WBGT requires a series of instruments, including a
black globe thermometer, a natural (static) wet-bulb thermometer, and a dry-bulb thermometer, and a
specific operating procedure.

There are, however, small portable units that include a microprocessor that will conduct the test and
correlate the information for you. A portable WBGT heat stress monitor, utilizing wet bulb, dry bulb and
globe temperature sensing elements which are connected to a meter, which has either a dial or digital
display for the readings, and is pre-marked to indicate heat stress levels, should be an essential item of
equipment on every work site in which excessive heat may be an important factor.

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