I've never really had to cope with a major disaster, but in the local scenes with which I have been involved, correcting the condition creating the anxiety is important, as well as sorting out the situation, and taking effective action to care for injured victims seems to help. Basically, impose order on chaos, and then demonstrate to anxious people that things are working once more, and that there is a task they can accomplish to help.

Isn't that why husbands, in an emergency childbirth situation, are always detailed to boil water?