When you’re a police officer, a traffic stop can mean a routine exchange— or it can mean an attack on your or your partner’s life.

Being first on the scene, whether for gruesome murders, suicides, plane crashes or car accidents, is all in a day’s work for police officers. But for many, there’s a limit to how much tragedy they can take.

The tipping point for many cops — whether it comes as they witness their first or hundredth incident — can lead to post-traumatic stress disorder (PTSD).