Firefighter health - FIREPROOF

The clinical question

It has been known for some time that the leading cause of death among serving firefighters is cardiovascular events, such as heart attacks, and not fire-related injuries as some people might assume. This is despite firefighters having regular health and fitness checks.

Professor Nick Mills and his team at the University of Edinburgh carried out the ‘Effect of Real-fire Training on Vascular Function’ (FIREPROOF) trial, funded by the BHF, to find out why.

What did the study involve?

The study, which ran from 2012 to 2013, recruited 19 healthy firefighters serving in the Scottish Fire and Rescue Service. The volunteers attended the study on two separate occasions, at least a week apart. 

• In one session, they participated in a fire training exercise at the Scottish International Fire Training Centre in Edinburgh. During the fire training exercise, they put out a fire and “rescued” an 80kg dummy from a two-storey structure. The firefighters were exposed to temperatures above 400°C during this exercise. 
• In the other session, firefighters undertook ‘light activity’, similar to tasks performed during a shift without emergency duties.

Before, during, and for 24 hours after each session:

• The firefighters wore heart monitors. The monitors continuously assessed their heart rate and rhythm, and the strength and timing of electrical impulses passing through their heart.
• The amount of sweat the firefighters lost was recorded.
• Samples of their blood were taken to test for markers of heart damage and to see how easily blood clots formed.
• The researchers measured the ability of the firefighters’ blood vessels to relax. 

What did the study show?

• The core body temperatures of the firefighters who took part in the fire simulation exercise increased by around 1 degree Celsius compared with their body temperature when they took part in light activity.
• Their body temperature remained high for three to four hours afterwards. 
• By measuring the firefighters’ heart function and testing for markers of heart damage, they also showed that exposure to fire simulation causes minor injury to the heart muscle in these otherwise healthy firefighters.
• Compared with the light activity session, their blood vessels were less able to relax in response to medication after the fire simulation. Their blood also became ‘stickier’ and more likely to form potentially harmful clots. 

The researchers believe that the increase in clotting was caused by a combination of fluid loss due to sweating and an inflammatory response to the heat of the fire. This leads to the blood becoming more concentrated and more likely to clot.

Why is the study important?

The FIREPROOF study suggested that these effects on the heart, vessels and blood, as well as the added stress of dealing with an emergency, may combine to increase the risk of cardiovascular events in firefighters. Professor Mills explained: "Studies from the USA have shown that nearly half of all firefighters who die on duty are killed by heart disease."

He added: "We've also found that there are simple measures, such as staying well hydrated, that firefighters can take to reduce their risk of heart attack."

The researchers therefore suggest that the time each individual firefighter spends tackling a blaze should be limited. They should also drink plenty of fluids and take time to cool down after putting out a fire. This advice can apply to anyone taking part in strenuous activity in a high temperature environment, such as endurance running in the summer months.

Study details

"Fire-fighters and acute myocardial infarction: understanding the mechanisms and reducing cardiovascular risk"
Award reference: PG/11/27/28842
Principal Investigator: Professor Nicholas Mills, University of Edinburgh
Trial registration number: NCT01812317

Publication details

Hunter AL, Shah AS, Langrish JP, et al. Fire Simulation and Cardiovascular Health in Firefighters. Circulation. 2017;135(14):1284-1295.