The TLVs Fail to Maintain Body Core Temperature within Safe Limits in Older Adults
Bibliographic record
Abstract
Industries rely on the American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs) to manage the health and safety of workers in hot conditions. A key shortcoming of the TLVs is the assumption that the guidelines are generalizable to broad population groups and do not consider age-related impairments in heat dissipation. PURPOSE: To evaluate core temperature and change in body heat storage during work in the heat using the TLVs, which are designed to ensure that a stable core temperature (and therefore heat balance) is achieved and remains below 38°C. METHODS: Nine older (58 ± 5 yrs) males performed three 120-min work bouts consisting of cycling at a fixed rate of heat production (360 W) under increasing ambient temperatures. Based on the TLVs, each protocol consisted of different work-to-rest (WR) ratios performed at different wet-bulb globe temperatures (WBGT). The first was 120-min of continuous (CON) cycling at 28°C WBGT while two protocols consisted of intermittent work bouts (15-min duration) adjusted for increases in WBGT: i) WR of 3:1 at 29°C (WR3:1) and ii) WR of 1:1 at 30°C (WR1:1) (equivalent exercise time of 90 and 60-min, respectively). Rectal (Tre) and mean skin temperatures were measured continuously and used to calculate the change in mean body temperature (ΔTb). The change in body heat storage was determined via direct calorimetry and subsequently used to calculate ΔTb. RESULTS: Heat balance was not achieved during exercise in any work conditions as the rate of change in Tre was greater than 0°C·min-1 (all P ≤0.05). As a consequence, mean Tre exceeded 38°C; albeit, time for Tre to exceed 38°C decreased as total exercise time increased (CON: 53 ± 7; WR3:1: 79 ± 12; and WR1:1 100 ± 29 min). Moreover, a greater ΔTb was observed with calorimetry relative to thermometry in all work protocols during the first 15-min of exercise [thermometry vs. calorimetry; CON: 0.21 ± 0.07 vs. 0.45 ± 0.06°C (P<0.01); WR3:1: 0.18 ± 0.05 vs. 0.51 ± 0.06°C (P<0.01); and WR1:1: 0.20 ± 0.06 vs. 0.50 ± 0.09°C (P<0.01)]. CONCLUSION: We show that the TLVs do not adequately protect older workers from potentially dangerous increases in core temperature during moderate work in the heat. Supported by the Ontario Ministry of Labour, Electric Power Research Institute and Natural Sciences and Engineering Research Council of Canada.
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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 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".