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

Trial Summary

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 data supports the effectiveness of the treatment Gradual Heat Condition, Rapid Heat Condition for reducing firefighter injury risk?

The research suggests that understanding and measuring heat tolerance through indices like the Thermal-Circulatory Ratio (TCR) and Physiological Strain Index (PSI) can help identify individuals at risk of heat-related injuries. These indices can guide the development of heat acclimatization strategies, which may be similar to the Gradual and Rapid Heat Conditions, to improve safety and performance in hot environments. ^{1 2 3 4 5}

Is the heat stress treatment generally safe for humans?

The studies show that firefighters experience significant heat strain, with increased core and skin temperatures and heart rates during firefighting activities. While these studies focus on physiological responses rather than safety, they highlight the importance of monitoring heat stress to prevent heat-related illnesses. ^{1 4 5 6 7}

How does the treatment for heat stress effects on firefighter injury risk differ from other treatments?

This treatment is unique because it focuses on practical cooling strategies specifically designed for firefighters to reduce heat strain and improve performance during firefighting tasks. Unlike other treatments, it incorporates the Adaptive Physiological Strain Index (aPSI) to provide a more accurate measure of physiological strain by considering skin temperature, which is crucial for those wearing protective clothing. ^{1 5 6 8 9}

What is the purpose of this trial?

This study will examine the effect of heat stress on factors that influence musculoskeletal injury risk in firefighters. Participants will attend 4 data collection sessions. 1: informed consent, screening, and familiarization. 2: pre-tests (strength, balance, and movement quality). 3: heat stress (rapid or gradual) followed by post-tests (strength, balance, and movement quality). 4: heat stress (rapid or gradual) followed by post-tests.

Research Team

Erin McCallister, DPT

Principal Investigator

LSUHSC-Shreveport

Eligibility Criteria

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

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

Treatment Details

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.

Participant Groups

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+

Findings from Research

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]

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]

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]

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]

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]

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]

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]

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]

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]

References

1. England pubmed.ncbi.nlm.nih.gov

An experimental model of heat storage in working firefighters. [2008]

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

The thermal-circulatory ratio (TCR): An index to evaluate the tolerance to heat. [2020]

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

A basal heat stress test to detect military operational readiness after a 14-day operational heat acclimatization period. [2021]

4. Switzerland pubmed.ncbi.nlm.nih.gov

Simulated Firefighting Task Performance and Physiology Under Very Hot Conditions. [2020]

5. England pubmed.ncbi.nlm.nih.gov

Indices of physiological strain for firefighters of the Australian Defence Forces. [2021]

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

Physiological responses during shipboard firefighting. [2006]

7. England pubmed.ncbi.nlm.nih.gov

Risk for heat-related illness among wildland firefighters: job tasks and core body temperature change. [2020]

8. England pubmed.ncbi.nlm.nih.gov

Cooling strategies for firefighters: Effects on physiological, physical, and visuo-motor outcomes following fire-fighting tasks in the heat. [2022]

9. England pubmed.ncbi.nlm.nih.gov

The influence of short-term firefighting activity on information processing performance. [2022]