Consecutive Occupational Heat Exposure With and Without Overnight Cooling

Summary

Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers exposed to hot environments. Current occupational heat-stress guidelines are designed to limit excessive increases in core body temperature and physiological strain during work in the heat through the use of work-rest schedules. However, these guidelines are largely based on single-day heat exposures and assume that workers recover in cool indoor environments between shifts. During heat events, many workers may instead recover in homes or accommodations that remain overheated, particularly in the absence of air conditioning. Inadequate overnight cooling may impair the body's ability to dissipate heat, increase physiological strain, and reduce tolerance to heat exposure on subsequent workdays. Older adults may be especially vulnerable due to age-related impairments in heat-loss capacity. To date, the effects of recovering in an overheated indoor environment on physiological strain and thermoregulatory function during repeated occupational heat exposure remain poorly understood, limiting the development of evidence-based recommendations to protect workers during prolonged heat events.

The primary objective of this study is to determine whether overnight recovery in an overheated indoor environment increases physiological strain during repeated occupational heat exposure in older adults. Specifically, investigators will assess whether recovery at the recently proposed upper indoor temperature limit of 26°C and 45% relative humidity (RH) (PMID: 38329752) is sufficient to attenuate elevations in core temperature during subsequent work in the heat compared with recovery in an overheated indoor environment (31°C, 45% RH) representative of conditions commonly experienced during extreme heat events. Healthy older adults will complete two consecutive days and nights of simulated moderate-intensity occupational heat exposure, with overnight recovery occurring in either the 26°C or 31°C condition. Measures of core temperature, cardiovascular strain, heat-loss capacity, hydration status, sleep quality, cognitive function, mood, and perceptual responses will be assessed to determine the impact of overnight recovery conditions on responses to repeated heat exposure. Whole-body heat-loss capacity will also be evaluated before and after the exposure protocol as assessed during incremental, intermittent exercise protocol performed in an air calorimeter.

Conditions

• Body Temperature Changes
• Heat Stress
• Heat Exposure
• Heat Fatigue
• Work Related Stress
• Physiological Stress

Interventions

OTHER

Simulated occupational heat exposure with recovery at recommended indoor temperature limit

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol involving daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) at the recommended upper indoor temperature limit (26°C, 45% RH).

OTHER

Simulated occupational heat exposure with recovery in an overheated indoor environment

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol involving daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) in an overheated indoor environment (31°C, 45% RH).

Sponsors & Collaborators

• University of Ottawa

  lead OTHER

Study Design

Allocation

RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

SINGLE

Model

CROSSOVER

Eligibility

Min Age

50 Years

Max Age

70 Years

Sex

MALE

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2026-07-01

Primary Completion

2027-06-30

Completion

2027-08-31

Countries

• Canada

Study Locations