Work Duration 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, Hot environment exposure

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

Compensation: Varies

Number of Visits: 2

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial aims to find better ways to manage work and rest periods in hot environments, focusing on how long someone can work safely before needing a break. It examines how different work intensities affect body temperature and whether age impacts heat tolerance. Participants will be divided into two groups: younger adults aged 18-30 and older adults aged 50-69. Ideal participants are active, non-smoking individuals without pre-existing health conditions like diabetes or high blood pressure and who do not frequently work in hot conditions. As an unphased trial, this study offers participants the opportunity to contribute to important research that could improve safety and health guidelines for working in hot environments.

Will I have to stop taking my current medications?

The trial requires that participants do not use medications that significantly affect body temperature regulation, 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 this protocol is safe for assessing work duration in heat stress conditions?

Research has shown that working in hot conditions can affect health by raising body temperature, increasing blood flow to the skin, and making the heart beat faster. These changes can heighten the risk of heat-related injuries and illnesses. Workers in heat may also experience reduced physical strength and difficulty thinking clearly, which can lead to accidents or absenteeism.

Long-term exposure to heat might increase the risk of health issues like liver problems and skin cancer. This trial aims to determine how long people can safely work in the heat before needing a break.

The trial includes both younger and older adults, but only those who are healthy and without existing health conditions. As this is a simulation of working in heat, the conditions are controlled to ensure safety. While heat stress poses risks, the research seeks to find the safest balance between work and rest to mitigate those risks. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about this trial because it aims to explore how different age groups handle working in hot conditions, which could lead to better guidelines for work safety in heat stress environments. Unlike standard approaches that might not differentiate between age groups, this trial specifically compares the heat tolerance and work duration of younger adults (18-30 years) and older adults (50-69 years) without pre-existing health conditions. By doing so, researchers hope to identify age-specific strategies that could improve safety and performance for workers exposed to high temperatures.

What evidence suggests that this protocol is effective for managing heat stress in different age groups?

Research shows that working in high heat can make physical tasks harder and reduce productivity. Studies have found that heat stress can lower work performance by 30 to 40%. This trial will divide participants into two groups: younger adults aged 18-30 and older adults aged 50-69, both without pre-existing health conditions. Older and younger workers may react differently to heat exposure, with older adults possibly having more difficulty maintaining stable body temperature. Strategies like staying cool and drinking enough water can help manage these effects. Understanding how age and work effort level affect heat tolerance and recovery is important. ^{2 6 7 8 9}

Are You a Good Fit for This Trial?

This trial is for workers of various ages who can safely perform heavy-intensity simulated work in hot environments. It aims to refine guidelines for managing heat stress by considering individual differences like age.

Inclusion Criteria

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

Non-smoking individuals

I am either 18-30 or 50-69 years old.

Exclusion Criteria

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

I am not taking medication that affects my body's ability to regulate temperature.

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

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Initial Work Bout

Assessment of initial stay times for heavy-intensity work for a single work bout

1 day

1 visit (in-person)

Second Work Bout

Assessment of initial stay times for a second work bout preceded by an extended rest period

1 day

1 visit (in-person)

Follow-up

Participants are monitored for safety and effectiveness after work bouts

1-2 weeks

What Are the Treatments Tested in This Trial?

Interventions

• Simulated work in the heat

Trial Overview The study tests how long people can initially stay working in the heat before needing a break, and if recommended rest periods effectively control core body temperature during intense work bouts across different times and days.

How Is the Trial Designed?

Group I: Younger adults. Experimental Treatment 1 Intervention

Adults aged 18-30 years with no pre-existing health conditions

Group II: Older adults. Adults aged 50-69 with no pre-existing health conditions Experimental Treatment 1 Intervention

Adults aged 50-69 with no pre-existing health conditions

Who Is Running the Clinical Trial?

University of Ottawa

Lead Sponsor

Trials

231

Recruited

267,000+

Published Research Related to This Trial

A study of 31,642 heat stress illness cases among active duty servicemembers from 1998 to 2019 found that higher daily heat indices, particularly maximum wet bulb globe temperature (WBGT) and heat index, significantly increase the risk of heat-related illnesses, with risks nearly doubling at higher temperatures.

The research suggests that prevention strategies should consider previous day's heat levels and monitor various heat indices, not just WBGT, to better assess risks and implement effective control measures for heat stress illnesses.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat stress morbidity among US military personnel: Daily exposure and lagged response (1998-2019). Lewandowski, SA., Shaman, JL.[2022]

The study developed advanced equations to accurately quantify physical work capacity (PWC) under varying heat stress conditions, based on 338 work sessions in controlled environments, which is crucial for understanding the impacts of climate change on labor productivity.

The research found that PWC significantly decreases with rising heat stress, showing a 10% reduction at mild heat (WBGT = 18°C) and a staggering 78% reduction at extreme heat (WBGT = 40°C), highlighting the economic risks posed by global warming.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

An advanced empirical model for quantifying the impact of heat and climate change on human physical work capacity. Foster, J., Smallcombe, JW., Hodder, S., et al.[2023]

Occupational heat stress significantly raises core and skin temperatures, heart rate, and urine specific gravity in outdoor workers, while drastically reducing their capacity for manual labor and metabolic rate, as shown in a meta-analysis of 38 studies involving 2,409 workers.

Projected impacts of global warming suggest that outdoor workers will face even greater challenges in physical work capacity, leading to increased labor intensity beyond safe levels, highlighting the need for effective heat mitigation strategies like hydration and work-rest schedules.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis. Ioannou, LG., Foster, J., Morris, NB., et al.[2023]

The study evaluated heat stress indices among 184 workers in brick kilns in Qom, Iran, finding that the wet-bulb globe temperature (WBGT) index had the highest correlation with physiological parameters, indicating its effectiveness in assessing heat stress.

WBGT was determined to be the most valid and practical index for measuring heat stress in hot and dry workplace environments, due to its ease of use and strong correlation with workers' physiological responses.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Validating the Heat Stress Indices for Using In Heavy Work Activities in Hot and Dry Climates. Hajizadeh, R., Golbabaei, F., Farhang Dehghan, S., et al.[2022]

In a study of nearly 400 heat stress measurements over four years in Chennai's automotive industry, it was found that over 28% of workers were at risk of heat stress-related health issues, highlighting a significant occupational health concern.

The research underscores the importance of implementing simple control measures to reduce heat stress risks and emphasizes the need for comprehensive baseline data to assess the effectiveness of these interventions and predict future impacts from climate change.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Work-related heat stress concerns in automotive industries: a case study from Chennai, India. Ayyappan, R., Sankar, S., Rajkumar, P., et al.[2021]

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 17 surgical staff members, working in a hot operating theatre (34°C) led to significantly higher core temperature, heart rate, thermal sensation, and sweat loss compared to normal conditions (23°C).

While manual dexterity showed a tendency to be impaired in the hot environment, alertness improved for the more active subgroup, suggesting that while heat affects physical performance, it may not negatively impact cognitive function in all cases.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effects of a hot ambient operating theatre on manual dexterity, psychological and physiological parameters in staff during a simulated burn surgery. Palejwala, Z., Wallman, K., Ward, MK., et al.[2023]

Manual workers in high-risk occupations, such as farmers and construction workers, are increasingly vulnerable to heat stress due to rising temperatures from climate change, particularly in low-middle income countries.

The review of 55 studies highlights that the health impacts of workplace heat exposure are often underestimated, emphasizing the need for more research to understand how these workers adapt to extreme heat and to develop effective strategies for reducing heat exposure.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Health impacts of workplace heat exposure: an epidemiological review. Xiang, J., Bi, P., Pisaniello, D., et al.[2023]

In a study involving 26 firefighters, it was found that physiological heat strain, indicated by a higher core temperature, was significantly greater on the second day of back-to-back fire suppression work, despite no differences in hydration or heart rate between the two days.

Firefighters reported increased perceived exertion and thermal sensation on the second day, suggesting that even with full recovery, the demands of consecutive days of intense work can lead to greater heat strain and fatigue.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat Strain Is Exacerbated on the Second of Consecutive Days of Fire Suppression. Schlader, ZJ., Colburn, D., Hostler, D.[2022]

The perceptual strain index (PeSI) demonstrated a strong correlation (r = 0.94) with the physiological strain index, indicating it is a reliable measure for assessing heat stress in various thermal conditions.

PeSI can be effectively used to evaluate heat strain when other methods are unavailable, as it correlates well with physiological indicators like heart rate and oral temperature, making it a practical tool in workplace safety.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Validation of Perceptual Strain Index to Evaluate the Thermal Strain in Experimental Hot Conditions. Dehghan, H., Ghanbary Sartang, A.[2022]

In a study involving 50 young and older non-heat acclimatized men, the initial stay time for moderate-intensity work before needing heat-mitigation controls was found to be 111 minutes at 26°C WBGT, decreasing to 44 minutes at 32°C WBGT.

These findings provide important guidelines for managing occupational heat stress, indicating how long workers can safely perform tasks in varying heat conditions before their core temperature risks exceeding safe limits.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Initial stay times for uncompensable occupational heat stress in young and older men: a preliminary assessment. Notley, SR., Akerman, AP., Kenny, GP.[2021]

The study found that the average physiological responses to intermittent dynamic workloads (like treadmill walking) were similar to those of continuous dynamic work, suggesting that time-weighted averaging of workload can effectively assess thermal strain in industrial settings.

Including static loads (like weight holding) had little impact on overall physiological thermal strain, indicating that existing heat stress criteria for continuous dynamic workloads can also apply to intermittent combined workloads, as long as peak loading does not pose health risks.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Influence of intermittency and static components of work on heat stress. Graveling, RA., Morris, LA.[2008]

Citations

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