Page 210 - Safety Memo

damage.

Table 2
PERMISSIBLE HEAT EXPOSURE THRESHOLD LIMIT VALUES
(Values are given in degrees Fahrenheit WBGT)

WORK LOAD
Work Rest Regimen: Light Moderate Heavy
Continuous work 86.0 80.1 77.0
75% Work, 25% Rest each hour 87.1 82.4 78.6
50% Work, 50% Rest each hour 88.5 85.0 82.2
25% Work, 75% Rest each hour 90.0 88.0 86.0

The Threshold Limit Values in Table 2 are the time-weighted average (TWA) exposure for a normal 8-
hour workday and a normal 40-hour work week, to which nearly all workers may be repeatedly exposed
without adverse effect. Although there are built-in safety factors to guard against adverse effects to
moderate deviations from normal environments and workloads, the safety factors are not of such
magnitude as to take care of gross deviations. For example, continuous work at temperatures above 86º
Fahrenheit, or overtime extending the work week more than 25%, might be considered gross deviations.
In such instances, judgment must be exercised in the proper adjustments of the Threshold Limit Values.

Higher heat exposures than shown in Table 2 may be permissible when the work involved is an asbestos
abatement project. This is due to the fact that each of these workers are in an undergoing Medical
Surveillance Program, they have been properly acclimatized, and due to the type of work involved, it has
been established that these workers quickly become more tolerant to working in a hot environment than
the average worker. However, workers should not be permitted to continue their work, when their deep
body temperature exceeds 100.4º Fahrenheit.

WORKER MONITORING
Weight Loss Monitoring
Measure the employee's weight on an accurate scale at the beginning and end of each work day to
determine if adequate fluids are being taken to prevent dehydration. The body water loss should not
exceed one and a half percent total body weight loss in a single day. Anything above this, should be
considered excessive and may require the employee's removal from the hot environment until lost
fluids are replaced and the worker's body weight is again within acceptable limits. Overnight rest and
proper diet are generally sufficient to bring body weight back to normal.

Note: If the daily starting weight one day is less than the starting weight of the previous day:
 A re-weigh should be made to verify scale accuracy; and

 Worker should be moved to a less heat intensive job until weight stabilizes.

Frequency of Heart Rate Monitoring
Workers wearing normal work clothing should be monitored whenever the dry bulb temperature
exceeds 70° F and workers wearing impermeable protective work clothing should be monitored
whenever the dry bulb temperature exceeds 60° F. To determine the workers heart rate, count the
workers radial pulse for 15 seconds and then multiply the number by four. The frequency of the heart
rate measurements should be according to acceptable Tables.

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