Initial Stay Times For Heavy-Intensity Work In The Heat For Young And Older Adults
Bibliographic record
Abstract
Workplaces rely on upper heat stress limits recommended by regulatory agencies to mitigate increases in core temperature above safe limits (≥1 °C above resting) during work in the heat to safeguard the health of workers. However, no guidance is provided on how much work can be performed before heat-alleviation controls (work/rest allocations) should be employed (termed the initial stay time). Current guidelines also fail to consider age-related declines in thermoregulatory function that can reduce heat tolerance. These are important knowledge gaps, as stay times that are too long may lead to core temperatures exceeding recommended limits whereas productivity may be limited if stay times are too short. While preliminary estimates for initial stay times for moderate-intensity work have been introduced, those for heavy work remain undefined. PURPOSE: To establish initial stay times for heavy-intensity work in warm to hot ambient conditions for young and older adults. METHODS: On three randomized days, 12 young adults (6 female, median (IQR) 24 (22-26) years; VO2peak: 48.9 (43.5-53.3) mL/kg/min) and 11 older adults (5 female, 65 (63-66) years; VO2peak: 33.5 (27.6-40.3) mL/kg/min) performed heavy-intensity work (fixed metabolic heat production of 260 W/m2) in wet-bulb globe temperatures (WBGT) of 26, 29 and 32 °C. Work continued until core (rectal) temperature increased +1 °C from baseline resting. RESULTS: A temperature by group interaction for stay time was observed (P < 0.01). Stay time decreased with increasing temperatures in young (P < 0.01) but not older adults (P ≥ 0.21). In 26 °C WBGT, stay time was 1.7-fold [95%CI: 1.1, 2.6] (P = 0.02) greater in young (79 (61-115) min) compared to older adults (48 (39-58) min). Conversely, stay time was not different in young versus older adults in 29 °C WGBT (50 (46-70) vs 40 (38-58) min; 1.3-fold [0.9, 1.7], P = 0.16) or 32 °C WGBT (42 (36-49) vs 42 (35-49) min; 1.0-fold [0.8, 1.2], P = 0.76). CONCLUSION: The time taken for core temperature to increase 1 °C declined with increasing WBGT in young but not older adults, such that stay times were greater in young adults in lower (26 °C WGBT) but not at higher ambient temperatures (29 °C and 32 °C WGBT). These estimates can help refine current heat stress management guidance to protect workers performing their duties in hot environments. Workplace Safety and Insurance Board (Ontario) and Mitacs
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".