Cooling Strategies for Heat Stress

Overseen By Glen P. Kenny, PhD

Age: 18+

Sex: Male

Trial Phase: Academic

Sponsor: University of Ottawa

Must not be taking: Antidepressants, Antihistamines, Diuretics

Disqualifiers: Diabetes, Hypertension, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: Unknown

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial aims to determine how different cooling methods help workers manage heat stress in hot conditions. Participants will test three cooling strategies: simulated work in the heat with no cooling during rest breaks, partial cooling during rest breaks (resting in the shade), and full cooling during rest breaks (resting in an air-conditioned space). The goal is to identify which method most effectively regulates body temperature. The trial targets adults who are active but not highly trained in endurance sports and do not frequently work or play in hot environments. As an unphased trial, it offers participants the chance to contribute to important research on improving workplace safety in hot conditions.

Will I have to stop taking my current medications?

The trial requires that participants do not use medications that significantly affect body temperature regulation and heat tolerance, such as antidepressants, antihistamines, and diuretics. If you are taking these types of medications, you may need to stop them to participate.

What prior data suggests that these cooling strategies are safe for workers?

Research has shown that cooling methods, such as sitting in air-conditioned rooms, effectively reduce heat stress. These techniques lower body temperature and heart rate, improving work performance in hot conditions. Studies confirm that body cooling methods are generally safe and decrease the risk of heat-related issues.

For partial cooling, like sitting in a shaded area with a fan, research suggests this can also lower body temperature during heat exposure. This approach is considered safe and enhances comfort and performance when working in the heat.

Both full and partial cooling strategies have been well-received in previous studies. No significant negative effects have been reported, making these strategies a safe option for reducing heat stress. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about this trial because it explores different cooling strategies to help manage heat stress, which is crucial for improving safety and performance in hot environments. Unlike the typical practice of using air conditioning or fans alone, this study looks at how varying levels of cooling—like sitting in air-conditioned spaces or just shaded areas with a breeze—affect people during rest breaks from intense work in the heat. By understanding the effectiveness of full, partial, and no cooling, this trial could lead to better guidelines for protecting workers and athletes from heat-related illnesses, ultimately helping to prevent overheating in a variety of settings.

What evidence suggests that this trial's cooling strategies could be effective for mitigating occupational heat stress?

This trial will compare different cooling strategies for managing heat stress. Participants in the "Full cooling" arm will sit in an air-conditioned room, a condition that studies have shown effectively lowers body temperature and boosts performance. Meanwhile, those in the "Partial cooling" arm will take breaks in the shade, a method that research suggests reduces the body's heat load. Both methods decrease physical stress and improve work performance in hot environments. These findings indicate that using cooling strategies during breaks can significantly help manage heat stress. ^{1 2 3 6 7}

Are You a Good Fit for This Trial?

This trial is for healthy adults who can safely perform moderate-intensity work in hot conditions. Participants should be able to tolerate heat and engage in simulated work tasks on a treadmill. Those with medical conditions that could be worsened by heat, or who cannot follow the study's procedures, are not eligible.

Inclusion Criteria

Non-smoking individuals

Habitually active individuals who are not endurance trained (less than 2 sessions per week, less than 150 minutes per week)

Ability to provide informed consent

Exclusion Criteria

I often work or spend time in hot places like saunas.

I have pre-existing conditions like diabetes or high blood pressure.

I am not taking medications that affect my body's ability to regulate temperature.

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Initial Stay Time

Participants perform continuous work until core temperature reaches 38.0°C or until volitional fatigue

Up to 240 minutes

Work-Rest Allocations

Participants complete a 180-minute work bout with a 1:3 work-to-rest allocation, with or without cooling strategies

180 minutes

Follow-up

Participants are monitored for physiological responses and safety after the work-rest allocations

1-2 weeks

What Are the Treatments Tested in This Trial?

Interventions

• Simulated work in the heat with full cooling during rest breaks
• Simulated work in the heat with no cooling during rest breaks
• Simulated work in the heat with partial cooling during rest breaks

Trial Overview

The study tests how effective different cooling strategies are during rest breaks for workers exposed to high temperatures. It compares no cooling, partial cooling (like sitting in shade), and full cooling (like being in an air-conditioned space) after working until they're too hot or tired.

How Is the Trial Designed?

Group I: Partial cooling Experimental Treatment 1 Intervention

Participants perform a continuous heavy-intensity work bout (metabolic rate of \~200 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 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work with 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).

Group II: Full cooling Experimental Treatment 1 Intervention

Participants perform a continuous heavy-intensity work bout (metabolic rate of \~200 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 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work with 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).

Group III: No cooling Active Control 1 Intervention

Participants perform a continuous moderate-intensity work bout (metabolic rate of \~200 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 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work without cooling.

Who Is Running the Clinical Trial?

University of Ottawa

Lead Sponsor

Trials

231

Recruited

267,000+

Published Research Related to This Trial

A systematic review of 44 studies found that while passive rest can reduce core temperature in heat-exposed individuals, the cooling rates are generally slow, averaging -0.002 to -0.070 °C per minute.

In conditions where workers wear insulative clothing, passive rest may not effectively lower core temperatures, with some datasets even showing stable or rising temperatures, highlighting the need for more effective cooling strategies in hotter environments.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest. Brearley, M., Berry, R., Hunt, AP., et al.[2023]

The study involving 10 male volunteers demonstrated that wearing a hybrid cooling vest, which combines air ventilation fans and frozen gel packs, resulted in a moderate cooling effect, reducing the rate of increase in core temperature and heart rate during exercise in a hot and humid environment.

Despite the cooling effect, the vest did not significantly hinder exercise performance, as measures of exercise duration, running distance, and perceived exertion remained similar between the cooling and non-cooling conditions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Reduction of Physiological Strain Under a Hot and Humid Environment by a Hybrid Cooling Vest. Chan, APC., Yang, Y., Wong, FKW., et al.[2019]

In a study involving nine healthy males, it was found that physical work capacity (PWC) decreased during a simulated work shift with repeated heat exposure, showing a 16% reduction in very hot conditions compared to cool environments.

The research suggests that existing models predicting PWC based on short-term heat exposure may need adjustments to account for the cumulative effects of heat stress over longer work shifts, especially after breaks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity. Smallcombe, JW., Foster, J., Hodder, SG., et al.[2022]

In a study involving 300 work trials across various temperatures (35-50 °C) and humidity levels (20-80%), it was found that increased air movement from fans can be ineffective or even harmful in hot environments, particularly when temperatures are 35 °C or higher and humidity is below 50%.

The research highlights that the effectiveness of fans for cooling is highly dependent on specific climate conditions, suggesting that public health guidelines should be updated to reflect these findings for better management of occupational heat strain.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Quantifying the impact of heat on human physical work capacity; part II: the observed interaction of air velocity with temperature, humidity, sweat rate, and clothing is not captured by most heat stress indices. Foster, J., Smallcombe, JW., Hodder, S., et al.[2022]

Occupational heat stress is expected to increase significantly in middle- and low-income tropical and subtropical regions due to climate change, posing serious risks to workers and economies.

There is a need for improved heat stress assessment methods and practical control strategies that consider worker acclimatization and resource availability, emphasizing collaboration among experts to effectively manage heat stress risks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Re-evaluating occupational heat stress in a changing climate. Spector, JT., Sheffield, PE.[2021]

A survey of 33 electric utility companies revealed that while 87% recognize heat stress as a workplace hazard and 78% have a heat stress management program, less than half actively monitor heat stress in real-time or track worker heat strain.

To improve worker safety in hot environments, a consensus-based approach is needed to standardize heat management practices across the industry, as many companies lack comprehensive monitoring and treatment protocols for heat-related illnesses.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

An exploratory survey of heat stress management programs in the electric power industry. Kaltsatou, A., Notley, SR., Flouris, AD., et al.[2021]

Cooling firefighters with a high-velocity fan during 10-minute rest periods significantly reduced their heart rates and rectal temperatures compared to normal recovery methods, indicating a safer approach to managing heat stress.

The study, involving 12 professional firefighters working in extreme heat (40°C and 70% humidity), suggests that without adequate cooling, prolonged firefighting can lead to dangerous levels of heat stress, even in physically fit individuals.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effectiveness of rest pauses and cooling in alleviation of heat stress during simulated fire-fighting activity. Carter, JB., Banister, EW., Morrison, JB.[2022]

The predicted heat strain (PHS) model allows for the creation of practical, localized guidelines for managing heat stress in the construction industry, enabling site supervisors to make quick decisions to protect workers.

Two specific heat stress management tools have been developed using the PHS model: one for optimizing work-rest schedules for paced work and another to help workers self-regulate during self-paced tasks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Application of the predicted heat strain model in development of localized, threshold-based heat stress management guidelines for the construction industry. Rowlinson, S., Jia, YA.[2014]

In a series of meetings with 115 stakeholders, including employers and policymakers, it was found that worker safety and health were prioritized over company profits, with an average rating of 9.1 for safety and 8.5 for health on a 10-point scale.

Despite the importance placed on health, 41% of respondents were unaware of any cooling strategies at their companies, and only 30% of those aware believed the interventions were effective, highlighting a significant knowledge gap regarding occupational heat stress mitigation.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Health vs. wealth: Employer, employee and policy-maker perspectives on occupational heat stress across multiple European industries. Morris, NB., Levi, M., Morabito, M., et al.[2023]

In a study comparing two cooling methods for relief from heat stress while wearing the USAF Chemical Defense Ensemble, both continuous cooling (CC) and intermittent cooling (IC) significantly improved work times and reduced final rectal temperatures, heart rates, and sweat production compared to no cooling.

Continuous cooling (CC) was found to be more effective than intermittent cooling (IC) in maintaining thermal comfort and reducing perceived exertion, indicating that applying cooling during both work and rest periods is beneficial for better thermal regulation in hot environments.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Continuous and intermittent personal microclimate cooling strategies. Bomalaski, SH., Chen, YT., Constable, SH.[2008]

Climatic heat stress significantly impacts construction site safety, leading to accidents due to heat-induced illness and fatigue, necessitating a complete overhaul of safety management systems rather than just incremental improvements.

The authors propose a three-level methodology for managing heat stress that includes controlling environmental exposure, regulating work time with mandatory breaks, and empowering workers to manage their own pace, emphasizing the need for region-specific practices tailored to local climatic conditions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Management of climatic heat stress risk in construction: a review of practices, methodologies, and future research. Rowlinson, S., Yunyanjia, A., Li, B., et al.[2014]

Citations

1.

clinicaltrials.gov

clinicaltrials.gov/ct2/show/NCT06630832

Study Details | NCT06630832 | Initial Stay Times and Heat ...

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

2.

pubmed.ncbi.nlm.nih.gov

pubmed.ncbi.nlm.nih.gov/40365833/

The Effects of Body Cooling Strategies on Physiological ...

We aimed to examine the effects of body cooling with cooling garments on physiological, perceptual, and performance outcomes during simulated work in the heat ...

3.

frontiersin.org

frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2023.1274141/full

The effect of heat mitigation strategies on thermoregulation ...

These data suggest that body cooling, hydration, and “shade” (removal of simulated radiant heat) as heat stress mitigation strategies should be considered.

4.

sciencedirect.com

sciencedirect.com/science/article/pii/S2093791125000241

Review Article Exploring Intervention Strategies to Prevent ...

This study aims to provide an overview of strategies to mitigate occupational heat stress, deliberately incorporating insights from other heat-vulnerable ...

5.

onlinelibrary.wiley.com

onlinelibrary.wiley.com/doi/10.1002/ajim.23734

The Effects of Body Cooling Strategies on Physiological ...

Body cooling garments reduced physiological responses while improving performance during simulated work in heat and should be considered an effective, low-cost ...

6.

pmc.ncbi.nlm.nih.gov

pmc.ncbi.nlm.nih.gov/articles/PMC10808760/

The effect of heat mitigation strategies on thermoregulation ...

To investigate heat stress mitigation strategies on productivity and thermoregulatory responses during simulated occupational work in the heat.

7.

sciencedirect.com

sciencedirect.com/science/article/abs/pii/S2352710224002535

Meta-analysis study on the effects of personal cooling ...

This study aims to evaluate the effectiveness of personal cooling strategies (PCSs) in reducing human heat stress, and determine the appropriate cooling ...