Heat Stress Effects on Firefighter Injury Risk

Overseen By Cory Coehoorn, PhD

Age: 18 - 65

Sex: Any

Trial Phase: Academic

Sponsor: Louisiana State University Health Sciences Center Shreveport

Disqualifiers: Recent injury, Pregnancy, others

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

Compensation: Varies

Number of Visits: 10

28 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial aims to understand how heat stress affects the risk of muscle and joint injuries in firefighters. Participants will experience varying levels of heat—either rapidly (Rapid Heat Condition) or gradually (Gradual Heat Condition)—while performing exercises. This approach helps researchers observe how heat influences strength, balance, and movement. Ideal participants are healthy professional firefighters who can safely exercise. As an unphased trial, this study allows firefighters to contribute to important research that could enhance safety and performance in their field.

Will I have to stop taking my current medications?

The trial information does not specify whether you need to stop taking your current medications.

What prior data suggests that these heat stress conditions are safe for firefighters?

Research has shown that firefighters often suffer from heat-related illnesses. One study found that 74.8% of firefighters reported symptoms of these illnesses, with some experiencing them frequently throughout the year. Sudden exposure to heat can be very hard on the body.

Firefighter protective gear has improved over time, reducing the risk of injuries from chemicals and extreme heat. However, the gear can still cause body temperature to rise quickly, which might be difficult for some individuals to handle.

Specific data on the safety of gradual heat exposure for firefighters is lacking. However, a gradual increase in heat might be easier on the body, allowing more time to adjust.

In summary, while sudden heat exposure can be tough on the body, protective gear and gradual heat exposure might help manage the risks. It's important to consider personal tolerance and health when deciding to participate in such studies. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about this trial because it explores how different heat exposure methods might impact firefighter safety. Unlike typical safety protocols, which may not differentiate between varying heat stress conditions, this trial examines both rapid and gradual heat exposure in controlled environments. By understanding how these distinct conditions affect core temperature and injury risk, researchers aim to improve safety measures and gear design for firefighters, ultimately reducing their risk of heat-related injuries.

What evidence suggests that this trial's heat stress conditions could affect injury risk in firefighters?

Research has shown that heat stress greatly increases the risk of injuries for firefighters. This trial will expose participants to different heat conditions to study these effects. Participants in the Rapid Heat Stress arm will experience sudden increases in heat, raising body temperature and heart rate, which puts extra strain on the body. This strain might reduce focus and decision-making, affecting physical performance. Meanwhile, participants in the Gradual Heat Stress arm will experience a more gradual increase in heat exposure, which might help the body adjust better, possibly reducing injury risk. Overall, heat stress is a major factor in injury risk during firefighting, and understanding its effects can help create better safety measures. ^{1 3 4 6 7}

Who Is on the Research Team?

Erin McCallister, DPT

Principal Investigator

LSUHSC-Shreveport

Are You a Good Fit for This Trial?

This trial is for firefighters who can safely undergo heat stress conditions. They'll participate in four sessions, including consent and pre-tests of strength, balance, and movement. The study excludes those with health issues that make heat exposure unsafe.

Inclusion Criteria

Professional firefighter

Healthy per the Physical Activity Readiness Questionnaire+ screening

Exclusion Criteria

Unable to swallow core temperature capsule

Unable to follow pre-testing hydration criteria

I've had a recent injury that affects my ability to move.

Timeline for a Trial Participant

Screening and Familiarization

Participants are screened for eligibility to participate in the trial and familiarized with outcome measures

1 week

1 visit (in-person)

Pre-test Data Collection

Participants complete pre-test data collection including strength, balance, and movement quality measures

1 week

1 visit (in-person)

Heat Stress Testing

Participants undergo heat stress testing with rapid and gradual heat stress conditions, followed by post-test measures

2 weeks

2 visits (in-person)

Follow-up

Participants are monitored for musculoskeletal injuries and other outcomes

24 months

Follow-up calls every 6 months

What Are the Treatments Tested in This Trial?

Interventions

• Gradual Heat Condition
• Rapid Heat Condition

Trial Overview

The study tests how rapid or gradual heat stress affects musculoskeletal injury risk factors in firefighters. Participants will be exposed to one of the two heat conditions before undergoing post-test assessments.

How Is the Trial Designed?

Group I: Rapid Heat Stress Experimental Treatment 1 Intervention

Participants in the rapid heat stress arm will perform an exercise protocol on a treadmill in a hot, humid environment while wearing firefighter protective gear. This results in an uncompensable heat environment with a rapid increase in core temperature.

Group II: Gradual Heat Stress Active Control 1 Intervention

Participants in the rapid heat stress arm will perform an exercise protocol on a treadmill in a hot, humid environment while wearing light exercise clothing. This results in an uncompensable heat environment but with a gradual increase in core temperature.

Who Is Running the Clinical Trial?

Louisiana State University Health Sciences Center Shreveport

Lead Sponsor

Trials

52

Recruited

19,400+

Published Research Related to This Trial

A study involving 301 wildland firefighters found that increased physical exertion during fire management tasks significantly raises core body temperature (Tc), with higher activity levels leading to greater temperature increases: 0.07°C for light, 0.19°C for moderate, and 0.44°C for high exertion tasks.

The research indicates that both the type of task and its duration affect the rise in Tc, suggesting that updated safety recommendations are necessary to protect firefighters from heat-related illnesses during their demanding work.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Risk for heat-related illness among wildland firefighters: job tasks and core body temperature change. West, MR., Costello, S., Sol, JA., et al.[2020]

A basal heat stress test (HST) can identify individuals at risk of heat intolerance during heat acclimatization (HA), with those showing higher rectal temperatures (Trec) and heart rates (HR) during the test being more likely to benefit from HA but still remaining less tolerant to heat afterward.

Participants with a basal Trec above 38.5°C after HA were classified as 'at risk', indicating that monitoring these physiological markers can help military personnel select individuals who are better prepared for operations in hot conditions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A basal heat stress test to detect military operational readiness after a 14-day operational heat acclimatization period. Malgoyre, A., Siracusa, J., Tardo-Dino, PE., et al.[2021]

U.S. Navy personnel experienced significant heat strain while fighting fires, with core temperatures reaching an average peak of 39.2°C and skin temperatures peaking at 39.5°C during intense firefighting activities.

The study quantified the rapid increase in heart rate (averaging 186 bpm) and body heat storage, highlighting the extreme conditions faced by firefighters, which can inform safety protocols and training for heat stress management.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Physiological responses during shipboard firefighting. Bennett, BL., Hagan, RD., Banta, G., et al.[2006]

The Adaptive Physiological Strain Index (aPSI) provides a more accurate assessment of physiological strain in firefighters wearing protective clothing compared to the traditional Physiological Strain Index (PSI), with aPSI ratings significantly higher during work activities.

In a study involving nine male firefighters, the aPSI indicated a greater level of strain, particularly when core temperatures approached occupational limits, suggesting it could better inform safety measures for firefighters in high-exertion scenarios.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Indices of physiological strain for firefighters of the Australian Defence Forces. Hunt, AP., Stewart, IB., Billing, DC.[2021]

In a study involving 14 firefighters, two practical cooling strategies (BASIC and ADV) significantly reduced core temperature and heart rate compared to a control method after simulated firefighting tasks in a hot environment.

Both cooling interventions improved thermal sensation, indicating enhanced comfort and safety for firefighters, although no significant differences were found in physical or visuo-motor performance outcomes.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Cooling strategies for firefighters: Effects on physiological, physical, and visuo-motor outcomes following fire-fighting tasks in the heat. Fullagar, H., Notley, SR., Fransen, J., et al.[2022]

The study developed a new index called the Thermal-Circulatory Ratio (TCR), which combines rectal temperature and heart rate to assess heat tolerance in individuals with a history of heat-related injuries, showing 100% sensitivity and 89% specificity at a TCR value of 0.279 °C/bpm after a 120-minute heat tolerance test.

Using a TCR threshold of 0.320 °C/bpm after 60 minutes can effectively identify heat tolerance with 100% sensitivity and 69% specificity, potentially allowing for a shorter and more efficient heat tolerance test for those who meet this criterion.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The thermal-circulatory ratio (TCR): An index to evaluate the tolerance to heat. Ketko, I., Eliyahu, U., Epstein, Y., et al.[2020]

Firefighters (FFs) performing tasks in 40 degrees Celsius while wearing personal protective equipment (PPE) experienced significantly higher core temperatures, with a maximum of 40.4 degrees Celsius, compared to 37.79 degrees Celsius without PPE, indicating that PPE increases heat stress.

The developed experimental model effectively simulates uncompensable heat stress (UCHS) in firefighters, allowing for controlled studies to improve work-rest cycles and rehabilitation conditions, which is crucial for their safety and performance during firefighting operations.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

An experimental model of heat storage in working firefighters. Van Gelder, CM., Pranger, LA., Wiesmann, WP., et al.[2008]

Firefighters performed 19% less work in very hot conditions (45°C) compared to temperate conditions (18°C), indicating that extreme heat significantly reduces physical performance during firefighting tasks.

Increased core and skin temperatures, along with higher heart rates and perceived exertion in the hot environment, highlight the need for fire agencies to prioritize safety and hydration for personnel working in extreme heat, as it can impact both health and productivity.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Simulated Firefighting Task Performance and Physiology Under Very Hot Conditions. Larsen, B., Snow, R., Williams-Bell, M., et al.[2020]

Simulated firefighting activities under heat stress improved reaction times immediately after the exercise, but these benefits diminished during recovery, indicating a temporary boost in attention that may not be sustained.

Incident rehabilitation (IR) did not influence performance, but factors like self-rated energy and conscientiousness were linked to reaction times, suggesting that individual psychological traits can affect cognitive performance in high-stress situations.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The influence of short-term firefighting activity on information processing performance. Greenlee, TA., Horn, G., Smith, DL., et al.[2022]

Citations

1.

pmc.ncbi.nlm.nih.gov

pmc.ncbi.nlm.nih.gov/articles/PMC6961651/

Functional Performance of Firefighters After Exposure to ...

Improvements in firefighter PPE have effectively reduced the risk of injury due to exposure to chemicals and extreme heat; however, PPE has been reported to ...

2.

withpower.com

withpower.com/trial/phase-heat-stress-disorders-6-2024-7e847

Heat Stress Effects on Firefighter Injury Risk

The studies show that firefighters experience significant heat strain, with increased core and skin temperatures and heart rates during firefighting activities.

3.

centerwatch.com

centerwatch.com/clinical-trials/listings/NCT06442956/effect-of-rapid-heat-stress-on-firefighters-musculoskeletal-injury-risk

Effect of Rapid Heat Stress on Firefighters Musculoskeletal ...

This study will examine the effect of heat stress on factors that influence musculoskeletal injury risk in firefighters.

4.

sciencedirect.com

sciencedirect.com/science/article/abs/pii/S037971122030758X

Firefighter neural function and decision-making following ...

Importantly, our results suggest that rapid heat stress and the resulting increase in physiological strain causes a decrease in cognitive control that could ...

5.

fsi.illinois.edu

fsi.illinois.edu/documents/research/fflsrc_finalreport.pdf

Firefighter Fatalities and Injuries: The Role of Heat Stress ...

The final section of Part 1 explores the role of heat stress and specifically proposes a model where heat stress influences cardiovascular events and the ...

6.

pmc.ncbi.nlm.nih.gov

pmc.ncbi.nlm.nih.gov/articles/PMC6546580/

Frequency of firefighters' heat-related illness and its ...

The results showed that 74.8% of firefighters experienced HRI symptoms and 5% of firefighters suffered from symptoms of HRI 20 times or more in a year.

7.

nfpa.org

nfpa.org/education-and-research/research/nfpa-research/fire-statistical-reports/firefighter-injuries-in-the-united-states

United States Firefighter Injuries | NFPA Research

An estimated 63,175 firefighters were injured in the line of duty in 2023, a decrease of 4 percent from the 65,650 injuries reported in 2022 ...