2007, Piran, Slovenia

Measurement methods
not included in the data analysis. The ANOVA based on the nested design indicated
significant effects for ensembles and heat stress level. While a significant difference was
detected by the ANOVA, Tukey's HSD did not distinguish among the ensembles. For the heat
stress levels, Tukey's HSD pointed to some overlap between pairs of ensembles and heat
stress levels, but generally each heat stress level was different from the others and the
ensembles within each heat stress level were not different.
Table 2. Mean (±standard deviation) for safe exposure time for the three clothing ensembles
by five heat stress levels.
Heat Stress Level Work Clothes NexGen Tychem QC
1 77.7±17.0 77.4±30.2 77.4±14.3
2 60.5±20.4 96.5 †±27.6 61.7±20.1
3 55.1±15.7 49.3±14.1 55.5±12.6
4 38.1±7.5 39.9±7.9 46.5±5.5
5 25.7±6.5 27.9±9.2 33.0±6.5
LS Mean 50.3 50.2 55.5
The actual WBGT was adjusted for the clothing using previously determined WBGT clothing
adjustment factors (Work Clothes: 0; NexGen: +2.5; Tychem QC: +7.5). The baseline
metabolic rate was taken as the average value, which was 188 W m -2 . The WBGT was
further adjusted by the difference from the average value by -0.039 °C-WBGT per W m -2 .
That is, the adjusted WBGT is increased if the trial metabolic rate was less than the average
and decreased if above average. The Adjusted WBGTs versus the exposure time limit are
shown in Figure 1. The equation for the protective limit line was fit subjectively to match the
lower times and include about 95% of the data above the line. The equation is:
Time Limit [min] = 22,000/(AdjWBGT [°C] - 27.5) 3 + 10(1)
DISCUSSION
An inspection of Table 2 suggests that each of the heat stress levels has about the same
average safe exposure time. There was some bias in the selection of WBGTs for each heat
stress level because NexGen and Tychem QC were targeted for lower WBGTs by 2.5 and 6.5
°C, respectively. For main effects, the Tychem had a higher LS mean than work clothes or
NexGen, and this appeared to be due to longer times in the two higher heat stress levels. The
Tukey's HSD analysis found no statistically significant differences among ensembles within
heat stress levels. Overall there is fair evidence to suggest that the clothing adjustment factors
apply to uncompensable heat stress as well as compensable heat stress near the occupational
exposure limit.
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