NCT06543719

Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part II

Safe Maximum Work Times and the Effectiveness of Work-rest Allocations in Mitigating Increases in Core Temperature During and on the Day Following Prolonged Heavy-Intensity Work in the Heat in Young and Older Workers

• Status: Completed
• Phase: N/A
• Study type: Interventional
• Enrollment: 21 (actual)
• Sponsor: University of Ottawa · Academic / Other
• Sex: Male
• Age: 18 Years – 69 Years
• Healthy volunteers: Accepted

Summary

Workplaces rely on upper heat stress limits provided by the American Conference of Governmental Industrial Hygienists (ACGIH) to manage the health and safety of workers in hot environments. This is primarily achieved by interspersing work with rest periods, the length of which is dictated by environmental conditions and work intensity, to maintain core temperature at or below 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels). However, these guidelines employ a "one size fits all" approach to exposure limits that does not consider individual variation (e.g., age) between workers. Moreover, they fail to provide direction on the safe, initial stay times before these heat-mitigation controls should be employed (i.e., rest breaks) in conditions exceeding upper heat stress limits. While recent work has generated estimates of the initial stay times for young to older men before heat-mitigation controls are required for moderate-intensity work, information on initial stay times for heavy-intensity work remains to be assessed. This project will assess the initial stay times for heavy-intensity work for a single work bout as well as for a second work bout that is preceded by an extended rest period such as a lunch break and a work bout performed on the next day to determine if refinements in initial stay times across these periods may be required. Further, the investigators will evaluate if the application of recommended work-rest allocations thereafter would alleviate increases in core temperature for the duration of the work period (e.g., start of shift versus post-lunch period). Given the known age-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will assess responses response in young and older adults.

Conditions

• Core Temperature
• Heat Stress, Exertional
• Heat Fatigue
• Exercise

Interventions

Type	Name	Description
OTHER	Simulated work in the heat	Participants perform a continuous heavy-intensity work bout (metabolic rate of \~260 W/m2) until core temperature reaches 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels), which is immediately followed by intermittent work using a 1:1 work-rest allocation, starting with a 30 min rest break followed by a 30 min work bout for a total work duration of \~240 min. The work protocol is performed in the morning of day 1, and repeated in a post-lunch work period (i.e., afternoon of day 1) and on the morning of the next day (i.e., morning of day 2).

Timeline

• Start date: 2024-07-25
• Primary completion: 2024-11-28
• Completion: 2024-11-28
• First posted: 2024-08-09
• Last updated: 2025-06-18

Locations

1 site across 1 country: Canada