There are essentially two different types of security guards, and they can be identified by whether or not they wear guns. An unarmed security guard is rarely in much danger, except from boredom. He wears a uniform and patrols a certain area like a watchman. If he spots any trouble he is generally expected to call the police and not take action himself. That is why some security guards can be quite old.
When a security guard wears a handgun in a holster, he is expected to use it against criminals if necessary. Chances are that the burglars or robbers will have guns too. So if a security guard is required to carry a gun he can be pretty sure that his is a dangerous job. Such a job should pay more money. Unarmed security guards generally get minimum wages and are near the bottom of the labor market.
Any profession can be hazardous and require much skill. Training for your profession is essential. When it comes to security, learning proper restraining techniques, problem solving strategies, proper weapon usage (if required) and being physically/emotionally healthy can reduce the risk of injuries and faults on the job. Hope this helped!