There are few jobs that come attached with more peril than firefighting.
But the greatest threat to a firefighter's life may not be smoke or flames. It could be his or her heart.
Just ask Ronald Browne, a former 3-star chief with the New York City Fire Department.
Browne says his heart attack occurred when he was at home but still on duty. There were warning signs, he says -- but he ignored them until the pain was too intense to bear.
"Fortunately my wife is a nurse," he says. "My wife said I turned ashen gray. She recognized the symptoms of a heart attack, and she called 911 right away."
Browne was rushed to the hospital, where doctors treated him for his heart attack. He survived, but the episode led to his retirement from firefighting.
Now, a new study shows that episodes like Browne's may be more common than once believed, suggesting a tremendous increase in risk of death from heart attack and other cardiac emergencies for firefighters on the job.
"Although people have been discussing this issue for the past 30 years, there wasn't any scientific background on it," says lead study author Dr. Stefanos Kales of the Harvard School of Public Health.
Kales' study examined duty-specific risks of death from coronary heart disease among on-duty U.S. firefighters from 1994 to 2004.
What he and his colleagues discovered was that heart disease causes 45 percent of the deaths that occur among U.S. firefighters while they are on duty -- making it the most frequent cause of death in this dangerous profession.
The study, which appears in the current issue of the "New England Journal of Medicine", found that firefighters, while fighting a fire, experienced a risk of heart attack anywhere from 12 to 136 times as high as when they were engaged in normal day-to-day activities.
Their chances of heart-related death were also 2.8 to 14.1 times as high while responding to an alarm, 2.2 to 10.5 times as high while returning from an alarm, and 2.9 to 6.6 times as high during physical training.
Kales says the findings suggest that the psychological stress and physiological demands of some of the profession's most crucial tasks combines with other individual lifestyle factors to increase the risk of heart attack.
It's not the type of working environment that OSHA would smile about.
Raging blazes and blankets of sulfurous smoke set the stage for firefighters, often carrying more than 50 pounds of gear, to perform a wide array of demanding and dangerous tasks.
"Firemen have a job which appears to involve periods of exceedingly high physical demand and stress interposed with longer periods of relatively sedentary work," says Dr. Jeffrey Brinker, professor of medicine and radiology at Johns Hopkins University.
"There is little time to 'warm up.' In addition, the exposure to smoke may decrease the oxygen available for respiration."
All of these external hazards combine with the internal threat of psychological stress and adrenaline -- a "perfect storm" of sorts for a deadly heart attack.
"This fits with the data indicating that the major cause of death in athletes over 35 years old is coronary heart disease," says Dr. Doug Zipes. "So strenuous exertion in 'older' men, if it causes a fatality, that fatality is more likely to be due to coronary heart disease than other factors."