In a study conducted collaboratively by the University of Cincinnati, Underwriters Laboratories and the Chicago Fire Department, researchers found exposure to harmful ultrafine air particulates could predispose firefighters to heart disease — particularly those in less-than-optimal personal health, said C. Stuart Baxter, associate professor in the university’s department of environmental health. Exposures can occur during the overhaul process when breathing apparatus often is removed.

The study was the first to characterize the size and distribution of particulates, including those in the ultrafine range, during domestic fires, Baxter said. Researchers conducted a series of simulated house and automobile fires to measure breathable particulates released during combustion and fire suppression, including the knockdown phase where firefighters are required to wear protective breathing equipment and the overhaul phase when they are not. He said researchers found that levels of ultrafine particulates invisible to the naked eye were highest during overhaul.

“This is the stage the firefighter may remove their equipment,” Baxter said. “A firefighter would normally assume he can breathe the air, but that may be a mistaken assumption.”

Instead, more than 70% of the particles in the air during overhaul were invisible, ultrafine particles that have been found to cause heart disease, Baxter said.

“We think firefighters should be aware that they should be wearing some breathing protection right through overhaul,” he said. “Air during overhaul is still hazardous to breathe.”

While it’s probably too much to ask a firefighter to wear heavy gear all the way through overhaul, which may last an hour or more, Baxter said firefighters should have breathing protection throughout the firefighting process. At least, firefighters should be encouraged to wear well-fitting masks with a filter. He also recommended chiefs swap out personnel during overhaul.

“Have firefighters with fresh air rotate in and bring the other ones out who have been working for awhile,” he said. “Of course, that will be difficult in these times, where unfortunately the fire service [personnel numbers] have been reduced.”