Resumen de Do the Threshold Limit Values for Work in Hot Conditions Adequately Protect Workers?.

Martin P. Poirier, Robert D. Meade, Andreas Flouris, Stephen G. Hardcastle, Glenn P. Kenny

• AB Purpose: We evaluated core temperature responses and the change in body heat content ([DELTA]Hb) during work performed according to the ACGIH threshold limit values (TLV) for heat stress, which are designed to ensure a stable core temperature that does not exceed 38.0[degrees]C. Methods: Nine young males performed a 120-min work protocol consisting of cycling at a fixed rate of heat production (360 W). On the basis of the TLV, each protocol consisted of a different work-rest (WR) allocation performed in different wet-bulb globe temperatures (WBGT). The first was 120 min of continuous (CON) cycling at 28.0[degrees]C WBGT (CON[28.0[degrees]C]). The remaining three protocols were intermittent work bouts (15-min duration) performed at various WR and WBGT: (i) WR of 3:1 at 29.0[degrees]C (WR3:1[29.0[degrees]C]), (ii) WR of 1:1 at 30.0[degrees]C (WR1:1[30.0[degrees]C]), and (iii) WR of 1:3 at 31.5[degrees]C (WR1:3[31.5[degrees]C]) (total exercise time: 90, 60, and 30 min, respectively). The change in rectal ([DELTA]Tre) and mean body temperature ([DELTA]Tb) was evaluated with thermometry. [DELTA]Hb was determined via direct calorimetry and also used to calculate [DELTA]Tb. Results: Although average rectal temperature did not exceed 38.0[degrees]C, heat balance was not achieved during exercise in any work protocol (i.e., rate of [DELTA]Tre > 0[degrees]C[middle dot]min-1; all P values <= 0.02). Consequently, it was projected that if work was extended to 4 h, the distribution of participant core temperatures higher and lower than 38.0[degrees]C would be statistically similar (all P values >= 0.10). Furthermore, [DELTA]Hb was similar between protocols (P = 0.70). However, a greater [DELTA]Tb was observed with calorimetry relative to thermometry in WR3:1[29.0[degrees]C] (P = 0.03), WR1:1[30.0[degrees]C] (P = 0.02), and WR1:3[31.5[degrees]C] (P < 0.01) but not CON[28.0[degrees]C] (P = 0.32). Conclusion: The current study demonstrated that heat balance was not achieved and [DELTA]Tb and [DELTA]Hb were inconsistent, suggesting that the TLV may not adequately protect workers during work in hot conditions.