JACKSONVILLE, Fla. -

Each year, Jacksonville firefighters respond to more than 115,000 calls for fires, car crashes and medical emergencies. But now they're doing it differently.

Recently, the department has started classifying its calls into two different priorities: hot and cold. Hot refers to dire emergencies where time is of the essence. Cold refers to less dangerous situations.

So if a call goes out as a cold response, generally, two firefighters in an ambulance running without their lights and sirens on will respond. But if it's upgraded to a hot response, those two firefighters and the ambulance, as well as additional firefighters in a fire engine will respond full speed with lights and sirens on.

The new system has been used by rescuers across the country but has gotten some criticism. Jacksonville fire union President Randy Wyse says having fewer firefighters respond could cause problems.

"They can do a whole lot more with more hands on the scene quicker," Wyse said.

Wyse said there have already been instances where a call has been classified by dispatchers as a cold response but has turned out to be a matter of life or death.

"It was a cardiac arrest. It came in as a cold call," Wyse said.

He said luckily rescuers went with their gut and requested backup. But he believes it could have ended badly.

"Even if they called and said, 'Hey, I sprained my ankle three days ago. Can you come look at it?' our policy was to run lights and sirens," Jacksonville Fire-Rescue Chief Marty Senterfitt said.

Senterfitt said the new system makes sense and is very efficient. He believes it has actually made the city safer by not having rescue units speeding all over town for calls that aren't necessarily urgent.

"Yes, there's always this possibility that somebody might make a mistake, but think of the liability of running lights and sirens all over Jacksonville when we don't need to," Senterfitt said. "We don't want to cause accidents. We don't want people to get hurt when we have no reason to."