To measure the environmental conditions that contribute to heat stress, we used a Quest
Technologies QUESTemp°36 instrument to obtain the wet bulb globe temperature (WBGT)
at each work location and in cooling areas. The WBGT measurements were datalogged
at 1-minute intervals during the entire workday and also manually recorded by National
Institute for Occupational Safety and Health (NIOSH) investigators on a daily activity log for
each task. The daily activity log was also used to describe each work task, its duration, and
its estimated metabolic load (exertion level), and rest breaks. We classified metabolic loads
as rest, light, moderate, heavy, and very heavy on the basis of NIOSH and ACGIH heat stress
criteria, which are the same [NIOSH 2013; ACGIH 2014]. Because heat stress occupational
exposure limits (OELs) are based on 1-hour averages, we selected three employees whose
results (on day 1) showed three different exposure scenarios: (1) CBT and heart rate above
the excessive heat strain criteria, (2) heart rate above the excessive heat strain criteria, and
(3) no CBT or heart rate above the excessive heat strain criteria. We grouped their work
tasks into approximately 1-hour time periods over 1 day. We then calculated time-weighted
average (TWA) exposures for the duration of each task and the average estimated metabolic
rate, and compared it to work and rest schedules recommended by NIOSH and ACGIH
for acclimatized employees. All employees wore cotton work uniforms, so no clothing
adjustment to the WBGT was necessary [ACGIH 2014].