With cardiac failure as the No. 1 killer of firefighters — accounting for close to half of the line-of-duty deaths in the past four years, according to the U.S. Fire Administration — efforts are being made to try and change that.

A study released in March by the Harvard School of Public Health showed that firefighters on active duty face a heart attack risk up to 100 times greater than that of workers with non-emergency roles, according to a USA Today report.

The National Volunteer Fire Council has joined forces with fire departments across the U.S. to combat this. The council mailed out heart health information this month to all of the nation's 30,000 fire departments and issued a fitness challenge online. This followed a June alert from the National Institute for Occupational Safety and Health (NIOSH) urging fire departments to develop fitness programs and follow medical screening guidelines.

“Firefighters do have long periods of downtime, and that's followed by a sudden jolt when the alarm goes off,” said council spokeswoman Kimberly Ettinger. “They have to right away get in gear, and their adrenaline goes up. That's a lot of strain even for people who are in shape.”

One example of the measures fire departments across the country are taking involves the Orange County Fire Authority in Irvine, Calif., which is conducting research of its own to try to find out what factors may underlie the high heart attack rate among firefighters. In the study, 125 firefighters swallow a tiny transmitting device and go into a fire simulator in which researchers can measure the temperature in the building and the internal body temperature, according to USA Today.

Another example is in Denver, where the Fireman's Fund Insurance Co. put up $50,000 in March to help pay for heart scans for the city's more than 900 firefighters.