He’s been a firefighter for 31 years, all 31 of them served with Prince George’s County Fire Department – one of the busiest departments in the country.

But Melvin Batts was on a break when he did some potentially life-saving work.

“We transported a patient to the hospital, after we left the hospital we went to get a bite to eat,” he said.

Batts and his partner had just walked into the Subway on Greenbelt Road in Lanham, when their portable carbon monoxide detectors, which PGFD recently began carrying around with them at all times, started going off.

“It started chirping, like a smoke alarm chirps, and it read 70 parts per million,” he said. “Anything about 30 and something is wrong.”

So, 70 is just dangerous.

“They didn't know it,” Batts said. “They didn't know it because they didn't have meters.”

Carbon monoxide is odorless so without the detectors, it's not the sort of thing you'd know about until it's too late.

“You never know,” Batts said. “It's a silent killer.”

Firefighters evacuated the entire Aerospace Place shopping center before tracking the gas leak to a dry cleaning shop.

They shut the gas off and ventilated the buildings, allowing everyone to breathe in some fresh air and get back to work.

Then, Batts and his partner finally got back to lunch.