Skip to main content
OpenTrials
Completed

NCT Number: NCT06630832

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

Occupational heat stress directly threatens workers' ability to live healthy and productive lives. Heat exposed workers are at an elevated risk of experiencing impaired work performance and cognitive function leading to a greater risk of work-related injuries which includes traumatic injury and a myriad of pathophysiological conditions (e.g., heat stroke, acute kidney injury, adverse cardiovascular events). To mitigate the adverse health effects of occupational heat stress, safety organizations recommend upper limits for heat stress, typically defined by a worker's metabolic rate and the prevailing wet-bulb globe temperature (WBGT). In instances where the heat load created by the combination of work intensity, environment, and clothing worn exceed the upper heat stress limits (uncompensable heat stress), controls such as rest breaks are prescribed to limit increases in core temperature beyond recommended limits. While workers are encouraged to find shelter from the heat during a rest break, it is not always possible or feasible. Typically, workers may rest while remaining exposed to the heat, recover in a shaded area or rest in an air-conditioned room or vehicle. However, the effectiveness of these cooling strategies in mitigating the level of physiological strain experienced by the worker during prolonged work in a hot environment remains unclear. In this project, the investigators will assess the efficacy of the different cooling strategies in preventing excursions in core temperature beyond recommended limits (38.0°C) following the initial stay time for moderate-intensity work in hot ambient conditions (WBGT of 29°C; represents hot outdoor conditions experienced by workers in summers in Ontario, Canada) in context of the prescribed American Conference of Governmental Industrial Hygienists (ACGIH) work-to-rest allocation for unacclimated adults. On three separate days, participants will walk on a treadmill at a fixed metabolic rate of 200 W/m2 until core temperature reaches and/or exceeds 38.0°C or until volitional fatigue. Thereafter, participants will complete an additional 180 min work bout employing the recommended ACGIH work-to-rest allocation of 1:3 (starting with a 45 min rest break followed by a 15 min work bout, with the cycle repeated three times over the 180 min work simulation bout) without (Control) or with cooling mitigation during each 15-min break consisting of either: i) partial cooling equivalent to sitting in a shaded space (WBGT 24°C; 31.7°C and 35% RH) such as under a tree with a light breeze (simulated with pedestal fan fixed at ~2 m/s) or ii) full cooling equivalent to sitting in air-conditioned space (e.g., room or vehicle) maintained at 22°C and 35% RH (equivalent WBGT of 16°C).

Completed

Looking for future studies?

Notify Me

Key information

Conditions

Body Temperature Changes Behavior Behavioral Symptoms Heat Exposure Heat Fatigue Heat Stress Heat Stress Disorders Hyperthermia Motor Activity Occupational Diseases Occupational Stress Pathological Conditions, Signs and Symptoms Signs and Symptoms Stress, Psychological Work Related Stress Wounds and Injuries

Age range

18 year–69 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

University of Ottawa

Ottawa, Ontario, K1N1A2, Canada

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • young (18-30 years) and older adults (50-69 years)
  • habitually active, not endurance trained (<2 sessions per week, <150 minutes per week)
  • non-smoking
  • English or French speaking
  • ability to provide informed consent

Exclusion criteria

  • pre-existing health conditions (e.g., diabetes, hypertension)
  • use of medication deemed to significantly modulate thermoregulatory function and heat tolerance (e.g., antidepressants, antihistamines, diuretics)
  • engaged in jobs and/or activities that involve frequent exposure to hot environments (e.g., regular sauna use)

Treatment and study plan

Simulated work in the heat with no cooling during rest breaks

Other

Young and older adults will not undergo cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).

Simulated work in the heat with partial cooling during rest breaks

Other

Young and older adults will not undergo partial cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).

Simulated work in the heat with full cooling during rest breaks

Other

Young and older adults will not undergo full cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).

Primary outcomes

  1. Initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (equivalent to a 1°C increase in body core temperature above resting levels) (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C (or relative increase of ≥1°C) is achieved or the absolute core temperature is <38°C (or relative increase of <1°C), the time of termination or end of the work bout will be taken as the initial stay time respectively).

  2. Average core temperature during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Average core temperature following initial stay time

  3. Heart rate at initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)

  4. Average heart rate during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Average heart rate following initial stay time

  5. Skin temperature at initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Skin temperature measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)

  6. Average skin temperature during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Average heart rate following initial stay time

  7. Thermal comfort scale at initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

  8. Thermal comfort scale during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

  9. Thirst sensation scale at initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

  10. Thirst sensation scale during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

  11. Rating of Perceived Exertion at initial stay time

    Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

  12. Rating of Perceived Exertion during work-rest allocations

    Time frame: Period of work-rest allocations over a 180 minute following the initial stay time

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

  13. Orthostatic Intolerance Symptoms Assessment

    Time frame: At the end of the 180 minute work-rest allocations

    Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort"

Sponsors and collaborators

Lead sponsor

University of Ottawa

Other

Registry information

Official study title

Impact of Partial and Full Cooling Applied During Prescribed Rest Breaks to Mitigate Increases in Physiological Strain During Prolonged Work in Hot Environments.

Important dates

Study start
2024
Primary completion
2025
Study completion
2025
First posted
Oct 8, 2024
Registry last updated
Jun 17, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

Related clinical trials

Published trials that share one or more normalized conditions with this study.