Miles Teller insists there is an ''extra obligation'' for actors when they are playing real people.

The 30-year-old actor is currently starring as real-life heroin addict turned firefighter Brendan McDonough in new movie 'Only the Brave'.

McDonough was the sole survivor of the 2013 Yarnell Hill Fire in Arizona which took the lives of 19 City of Prescott firefighters.

When making the movie, Teller became good friends with McDonough and he realised he had a duty to tell his story in a truthful and honest way.

Speaking to The I Paper, Teller said: ''There's an extra obligation when you're playing a real person. Friendship isn't a requirement; it's not by playing a person that we're gonna be friends. But I've been lucky to get to know some pretty incredible people and, for me, it doesn't stop when filming is done.''

Tellers - who stars alongside Josh Brolin in 'Only the Brave' - had to go through a boot camp, similar to what McDonough did himself to join the fire rescue service, and he found it inspiring that this man did the training while coming off heroin.

He said: ''Brendan was the source for me on that. It's not something he is proud of, but he made it through hotshot boot camp while detoxing off some heavy drugs. I went through a version of that boot camp and came into it healthy - and it was still pretty tough.''

The firefighters were given the nickname ''hotshots'' which in the name given to top wildland firefighters and filmmaker Joseph Kosinski said the way ''they fight fires is very different''.

Kosinski said: ''The way they fight fires is very different: they don't carry water; they fight fire with fire.

''They dig lines and cut down trees and try to establish a border. They light fires, back burns, that they use to battle against the wildfire.''