Sian Claire Owen, Medical Journalist for Cardio Debate

Firefighters risk their lives to keep us safe, but recent research confirms that some of the risks they face – the risk of heart attacks – are less obvious than others.

A recent study published in Circulation explores the link between firefighters and cardiovascular disease, finding a “direct link between physical activity levels and risk of heart attack.” [1]

Lead researcher Professor Nicholas Mills from The University of Edinburgh and the British Heart Foundation Centre for Cardiovascular Sciences tells Business Insider that: “Heart attacks are the most common case of deaths among on-duty firefighters. They are much more likely to occur during or shortly after work to subdue a fire.” [2]

Researchers studied 19 non-smoking, healthy, 17 of whom participated in two fire simulation exercises, each a week apart. The exercise exposed participants to temperatures reaching upward of 400 degrees Celsius (752°F) as they attempted to retrieve a “victim” (weighing roughly 176 pounds) from a two-story structure. Heart rate and blood pressure were monitored for 30 minutes before the exercises and for the following 24 hours. [3]

These conditions were shown to “activate platelets, increase thrombus formation, impair vascular function, and promote myocardial ischemia and injury in healthy firefighters.” [1]

Professor Mills says: “Lower blood pressure immediately following fire suppression is likely due to dehydration and an increase in blood being diverted to the skin to help the body cool down.

“We discovered the core body temperature increased, on average, nearly 2 degrees Fahrenheit over 20 minutes. And increases in hemoglobin occur as the body loses water and the blood gets more concentrated.”

They found that in addition to the potential for injury to the heart muscle that occurs during fire suppression, firefighters are also at risk of blood clotting.

“We assessed blood clotting in response to both extreme heat and physical exertion. In this setting an increase in blood clotting is likely an exaggerated normal physiological reaction to both these stressors,” said Mills. [3]

In the light of these findings, simple and effective measures can be taken to reduce the risk of cardiovascular events in this population. Essentially, anyone who is undertaking strenuous exercise in extremely high temperatures must rehydrate and take the time to cool down afterwards.


  1. Fire simulation and cardiovascular health in fire fighters. Hunter LA, Shah ASV, Langrish JP, et al., Circulation 2017; 135: 1284-95.