Do The National Institute Of Occupational Safety And Health Recommendations Prevent Hyperthermia And Dehydration?

Abstract

Listen

Translate article

The National Institute of Occupational Safety and Health (NIOSH) recommendations for work in the heat suggest consuming 237 mL of water every 15-20 min and rest intervals are not necessary for work if conditions are not extreme. The efficacy of these recommendations to protect against hyperthermia (rise in core temperature) and dehydration (percent body mass loss) has not been tested. PURPOSE: To test the effectiveness of the NIOSH guidelines to prevent body temperature from exceeding 38.0°C and dehydration greater than 2% of body mass. METHODS: Seven men walked for 2 hours at 6.4 kph in the highest thermal stress NIOSH allows before recommending work-to-rest ratios (34°C, 30% relative humidity). Participants drank 237 mL of water every 20 minutes while rectal temperature (Tre) monitored. Body mass and urine specific gravity (USG) were measured before and after exertion. Tre was extrapolated out to four- and eight-hour workdays based on the rate of Tre rise in the last hour of exertion. Percent dehydration was extrapolated out to four- and eight-hour workdays based on body mass lost and planned hydration during exertion. RESULTS: Tre rose from baseline (36.8±0.3°C) to the completion of exertion (38.1±0.6°C, p<0.001), with two subjects reaching the 38°C threshold. Four- and eight-hour predicted Tre were 38.6±1.1°C and 39.6±2.1°C, respectively, with 5 subjects predicted to exceed Tre threshold at 4hr and 6 subjects at 8hr. Subjects began work euhydrated (USG: 1.013±0.005) and dehydrated 0.03±0.48% during the work protocol, with no subjects reaching 2% dehydration. Four- and eight-hour predicted percent dehydration were 0.05±0.95% and 0.10±1.90%, respectively. CONCLUSIONS: Adherence to the NIOSH recommendations may be insufficient to prevent workers from reaching the hyperthermia threshold but would protect against dehydration during heavy intensity work in the heat. Adjustments to NIOSH work-to-rest ratio recommendations should be explored to maintain worker safety.