Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part I
- Conditions
- Core TemperatureHeat Stress, ExertionalExerciseHeat Fatigue
- Interventions
- Other: Simulated work in the heat
- Registration Number
- NCT05847712
- Lead Sponsor
- University of Ottawa
- Brief 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 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, this information is limited to a single work bout and does not consider a second work bout preceded by an extended rest period (e.g., lunch) or next day effects. This is a key consideration, as prolonged work in the heat has been shown to cause next-day impairments in heat dissipation in older men. Further, it remains unclear if the application of the prescribed ACGIH 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). This project will address these knowledge gaps by determining if refinements in initial stay times for moderate-intensity work (represents the average work effort of physically demanding occupations) in the heat (26°C wet-bulb globe temperature) may be required for young and older adults for i) a second work bout that is preceded by an extended rest period such as a lunch break, and ii) a work bout performed on the next day. This includes assessing the efficacy of the prescribed ACGIH work-rest allocations to mitigate increases in core temperature beyond safe limits (\>38.0°C, equivalent to a \>1°C increase in body core temperature above resting levels) during these work periods. Given the known sex-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will conduct separate analysis to identify modulating effects of biological sex on the initial stay times and effectiveness of the work-rest allocation as a heat-alleviation control.
- Detailed Description
Not available
Recruitment & Eligibility
- Status
- COMPLETED
- Sex
- All
- Target Recruitment
- 60
- 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
- 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)
Study & Design
- Study Type
- INTERVENTIONAL
- Study Design
- PARALLEL
- Arm && Interventions
Group Intervention Description Older adults Simulated work in the heat Adults aged 50-69 with no pre-existing health conditions Younger adults Simulated work in the heat Adults aged 18-30 years with no pre-existing health conditions
- Primary Outcome Measures
Name Time Method Initial stay time End of third (morning day 2) continuous work bout 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).
Average core temperature Period of work-rest allocations following initial stay time for morning day 2 Average core temperature following initial stay time
- Secondary Outcome Measures
Name Time Method Average skin temperature Period of work-rest allocations following initial stay time for morning day 2 Average skin temperatures following initial stay time
Skin temperature at initial stay time End of third (morning day 2) continuous work bout Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)
Systolic blood pressure End of third (morning day 2) work period Arterial blood pressure measured via automated oscillometry
Rate pressure product End of third (morning day 2) work period Calculated as systolic blood pressure \* heart rate
Orthostatic Intolerance Symptoms Assessment Period of work-rest allocations following initial stay time for morning day 2 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".
Heart rate at initial stay time End of third (morning day 2) continuous work bout Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)
Fluid loss End of third (morning day 2) work period Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).
Change in plasma volume End of third (morning day 2) work period Determined from venous blood samples
Thirst sensation scale Period of work-rest allocations following initial stay time for morning day 2 Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Average heart rate Period of work-rest allocations following initial stay time for morning day 2 Average heart rate following initial stay time
Diastolic blood pressure End of third (morning day 2) work period Arterial blood pressure measured via automated oscillometry
Mean arterial blood pressure End of third (morning day 2) work period Calculated as 1/3 \* systolic blood pressure + 2/3 \* diastolic blood pressure
Fluid consumption End of third (morning day 2) work period Cumulative fluid consumption calculated by weighing the participant's water intake
Rating of Perceived Exertion Period of work-rest allocations following initial stay time for morning day 2 Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Thermal comfort scale Period of work-rest allocations following initial stay time for morning day 2 Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Trial Locations
- Locations (1)
University of Ottawa
🇨🇦Ottawa, Ontario, Canada