Tim O’Brien is a third generation firefighter.

He offered to gather some coworkers to watch the pilot episode of “Chicago Fire” and give an insider perspective on how closely the show resembles the real thing.

The new NBC drama centers around the Chicago Fire Department. It premieres Wednesday at 9 p.m., but the first episode was available On Demand and online ahead of the air date.

So earlier this week O’Brien served up some homemade beef vegetable soup. He relegated his two dogs - Shadow and Irish - into the backyard. He threw a log into the fireplace and everyone settled into his living room for the show.

Pat Duddleston, a 22-year Fire Department veteran, lives just down the street from O’Brien. He’s with Truck 17 on the South Side.

Rebecca Bolluyt is a paramedic from Uptown.

The real firefighters watched their fictional counterparts respond to car crashes, house fires and gunshot wounds.

O’Brien said the biggest difference between real fires and the fires on television is the amount of smoke on a scene.

 “A lot more smoke (in real fires),” he said. “But…you can’t watch the show if all you can see is smoke.”

No matter how intense the action got on the screen, they always seemed to be able to top the scripted stories with real life experiences.

“You ever have one who was shot in the head talking to you?” O’Brien asked the others. “I had one once. Real small caliber bullet from far away. It broke the skin but didn’t penetrate his skull. It was the weirdest thing in the world.”

Some moments got big laughs - like when when the wide-eyed rookie character gets stuck with some grunt work.

“That’s true,” O’Brien said. “That’s exactly how it goes. That would happen.”

Duddleston said the show does a good job of showing how the fire department is like a family.

“A lot of people don’t understand it cause everybody goes to a nine to five job and they’re done,” he said. “Here we spend one third of our lives with these guys and girls. It’s brothers and sisters.”

Bolluyt said she likes that the show focuses on how the job bleeds into firefighters’ personal lives too.

“I know other people have stressful jobs,” she said “But we’re with each other in some of the most extreme, most stressful situations that you could ever be with someone in and it makes you become closer to other people.”

The very unscientific focus group gave the show passing marks for its portrayal of life in the firehouse.

The NBC show, from creator Dick Wolf, has used real Chicago locations for much of its filming. Mayor Rahm Emanuel makes a cameo in the pilot too.

O’Brien said even the set decorations were authentic - real calendars, posters and old photos hang on walls in the background.

But the real firefighters couldn’t help laughing at some of the Hollywood touches - like when the first chiseled actor sauntered on screen without a shirt.

“That’s the way I looked when I came on the job,” O’Brien said. “And I used to walk around with my shirt off. But now that I look like this, I leave it on.”