(CBS) -- Pulling the trigger on a gun can be a life and death decision. It's a decision police officers face on a daily basis.
How do they train to make sure they're making the right choice? CBS 2's Mai Martinez got a crash course from Chicago police.
The training scenario: a domestic dispute. It's a chaotic scene. As officers arrive at the door of the home, they see a man with a gun screaming at another man.
The two officers repeatedly order the armed man to drop his weapon. Finally he does, but he draws another and points it at the other man, prompting officers to open fire.
The man is hit but fires his weapon, shooting the other man. Both men fall to the ground.
It's a situation no officer wants to face -- the use of deadly force. Fortunately, this is only a training exercise and everyone lives.
That's not always the case in real life.
"No officer wakes up, goes to work, thinking, 'I'd like to get involved in a shooting today,'" explains Sgt. Larry Snelling, a supervising instructor at the Chicago Police Academy.
The purpose of the training scenarios is simple: expose recruits and officers to as many potential real-life situations as possible before they hit the streets. That way, when the moment comes they'll know whether or not to pull the trigger.
"It helps them and inoculates them to stress," says Officer Joseph Hancin, a tactics instructor at the Chicago Police Academy. "When you have people that are in front of you yelling or they have a weapon in their hand it's a different kind of stress."
Officers don't always make the right call. That's something Martinez learned first-hand when she was startled by a man with something in his hand as she ran to help another officer.
Martinez fired a practice gun. Only after the mock suspect hit the ground did she realize the man was only holding a cell phone.
"It's the closest thing we can get to reality," Hancin says.
The training is invaluable when officers respond to calls and have to decide in a split second whether they need to fire.
"Any hesitation in that officer's response could cost him his life or someone else's," Snelling says.
In another scenario, Martinez and her training partner arrived at the scene of a call for a man with a knife. As she tried to reason with the man to drop the knife, he lunged and "stabbed" her before she could draw her weapon.
That experience helped on the next drill: a carjacking scenario involving two armed offenders.
Knowing they were armed better prepared Martinez for what happened next. One suspect wouldn't stop coming toward her even as she called for him to halt.
The man kept walking and shouted, "I'm not going to jail."
As he reached into his pocket, Martinez shot him once.
The man fell as he pulled a cell phone out of his pocket, but a pat-down revealed the real danger: a gun under his sweatshirt, tucked into his waistband.
"A police officer goes out every day to do the job. He never knows if he's going to come back home," Snelling says.
Martinez received about 30 minutes to 45 minutes of training before being dropped into the scenarios.
Recruits at the Chicago Police Academy receive between 900 and 1,000 hours over six months before they're put on the streets as probationary police officers.
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