Deb, most people simply make a walking surface using 3/4" plywood layed over the joists. Just try to keep it away from any exposed wiring. As for it being a fire hazard, no more so than the rest of your house, the joists are wood, as are the studs inside of your walls, and the subflooring throughout the whole house. If you want to tack the electrical wires to the joists, DON'T staple them, you can buy insulated tacks at the hardware store, althougth unless the wires are in the way I wouldn't bother. Hope this helps, and watch out for whatever might be lurking up there after 30 years.