There's a beginners guide around somewhere that highlights the fact that the spark hazard to ignite a flammable gas is pretty comparable in energy to the shock hazards to humans. I haven't worked on stuff that presents a serious shock hazard, but I have done some intrinsically safe stuff. One technique to consider is just using an additional isolation transformer in the power path so that there is no current path when a user touches any single terminal. This is the concept used by shaver sockets in bathrooms.