A simulated office complex, made of plastic boxes, has been set up on the grounds of the Mid Valley Fire Training Academy near Del Rey in Fresno County.
Firefighters and deputies are being trained to work together in responding to "active shooter" situations.
A trainer describes the scenario: "You've been dispatched to a business, there's a report of someone inside the business shooting people, and there's multiple victims."
Law enforcement officers rush into real scenes like this with one goal in mind - to stop the killing.
But wounded victims can die waiting for emergency personnel to be able to enter.
Fresno County Fire Department Public Information Officer Michael Bowman says that is about to change.
"Historically the fire service has staged, outside the area and waited until law enforcement has secured the scene or neutralized the assailant. Now we are able to go in immediately to the scene."
Fresno County firefighters are being outfitted like combat medics, with supplies and bulletproof vests, enabling them to go in with deputies and render immediate assistance to survivors.
Fresno County Sheriff Margaret Mims explains why: "The goal is to save lives, so we don't have as many casualties. This program is unique."
Firefighters are used to risking their lives in dangerous situations, but Fire Chief Mark Johnson says training to face gunfire is something new.
"But it's necessary training in today's society that we are there to go in behind our sheriff's officers and provide life-saving medical attention to these victims when it does happen."
This training has been underway for 6 weeks.
It's expected that by August 1, all Fresno County Fire Department firefighters will be ready to face real situations like this.
Fresno County firefighters train to respond to shooting incidents