You are not being silly; it's right and good that you worry about your husband.
I'm sure that he will wear a harness & have it clipped in the proper safety-procedure way. If the harness works like a rock-climbing harness does, he won't fall far if (and only if) he falls - maybe 1 foot. (sorry if that does not help ease your mind).
I'm also sure the other crew members keep an eye out for each other.