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

20 Participants Needed

Trial Summary

What is the purpose of this trial?

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 (e.g., age) 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, information on initial stay times for heavy-intensity work remains to be assessed. This project will assess the initial stay times for heavy-intensity work for a single work bout as well as for a second work bout that is preceded by an extended rest period such as a lunch break and a work bout performed on the next day to determine if refinements in initial stay times across these periods may be required. Further, the investigators will evaluate if the application of recommended 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). Given the known age-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will assess responses response in young and older adults.

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 data supports the effectiveness of the treatment Simulated work in the heat for managing heat stress?

Research shows that occupational heat stress can increase body temperature and heart rate, which suggests that simulating work in the heat could help understand and manage these effects. Additionally, studies on heat stress indices and mitigation strategies provide insights into how to optimize work conditions in hot environments. ^{1 2 3 4 5}

Is it safe for humans to work in heat stress conditions?

Research shows that working in high temperatures can increase the risk of heat-related illnesses like heat stroke and heat exhaustion. Safety measures, such as monitoring heat levels and taking breaks, are important to prevent these risks. ^{2 6 7 8 9}

How does the treatment 'Simulated work in the heat' differ from other treatments for heat stress?

The treatment 'Simulated work in the heat' is unique because it involves mimicking real work conditions in a controlled environment to study the effects of heat on physical work capacity over a full work shift, unlike other treatments that may not replicate actual work scenarios. This approach helps in understanding how repeated work and rest cycles in varying heat conditions impact performance, which is not typically addressed by standard heat stress treatments. ^{1 6 10 11 12}

Eligibility Criteria

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

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

Treatment Details

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.

Participant Groups

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+

Findings from Research

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]

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]

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]

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]

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 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]

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]

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]

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]

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]

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]

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]

References

1. Iran pubmed.ncbi.nlm.nih.gov

Validating the Heat Stress Indices for Using In Heavy Work Activities in Hot and Dry Climates. [2022]

2. United States pubmed.ncbi.nlm.nih.gov

Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis. [2023]

3. United States pubmed.ncbi.nlm.nih.gov

Heat Strain Is Exacerbated on the Second of Consecutive Days of Fire Suppression. [2022]

4. United States 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. [2023]

5. Iran pubmed.ncbi.nlm.nih.gov

Validation of Perceptual Strain Index to Evaluate the Thermal Strain in Experimental Hot Conditions. [2022]

6. United States 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. [2022]

7. United States pubmed.ncbi.nlm.nih.gov

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

8. Canada pubmed.ncbi.nlm.nih.gov

Initial stay times for uncompensable occupational heat stress in young and older men: a preliminary assessment. [2021]

9. Japan pubmed.ncbi.nlm.nih.gov

Health impacts of workplace heat exposure: an epidemiological review. [2023]

10. England pubmed.ncbi.nlm.nih.gov

Influence of intermittency and static components of work on heat stress. [2008]

11. United States pubmed.ncbi.nlm.nih.gov

An advanced empirical model for quantifying the impact of heat and climate change on human physical work capacity. [2023]

12. United States pubmed.ncbi.nlm.nih.gov

Work-related heat stress concerns in automotive industries: a case study from Chennai, India. [2021]