This was a topic covered in NBC training when I was in the Army.
The biggest problem with any major trauma is that human beings in a state of intense shock or fearfulness have a very powerful compulsion to imitate the behaviour of others around them. So when you are triaging victims of a nerve gas attack you have to be alert for the subtle variations of soldiers simply acting like those around them by trembling violently and gasping and troops actually exposed to nerve agent.
This is also a big part of the necessary psychology of shelter captains. If you are ever in a leadership role, you have to understand the grave responsibility of staying ice cool at all times. Never allow yourself to be swept up in the natural hysterics that follow in human beings when they have undergone a terribly traumatic experience. People coming into the shelter will try to draw you into their emotional state, screaming and babbling about imagined as opposed to genuine ills they fear. Many people will enter the shelter mimicking radiation sickness when in fact they are fit as fiddles. Others will not feel secure even once they sit down and are settled. It is extraordinarily important for the shelter leader to always be a combination of Clint Eastwood and Spencer Tracy. Firm and understanding but resolute and as calm as an unrippled pond. If the shelter captain loses it, that gives carte blanche to the most manic characters to go right off the deep end, usually in situations that don't warrant it in the least. The initial few hours are the toughest period to get acclimated. That's why you should have comfort food, distractions and soothing music or quiet environments for them to settle down in. Giving somebody a job works wonders for them when they are frightened, it often takes their mind right off their ambiguous worries and allows them to focus on something close at hand.