Maybe add a fan? Keeping the air moving bound to help with heavy fumes finding the low place to congregate. Adding a CO2 or carbon monoxide monitor might help with unknowingly working in heavy concentrations of carbon monoxide. Adding a rail at each side to keep a tire from accidentally slipping off the edge. Adding a top that can support a heavy load when not in use to keep someone from accidentally walking off into it. Adding some cave-in protection might be a good idea too.....there are lots of common sense things that can be done to make a pit safer. My grandpa had one we all used as kids to work under the car. I remember leaning out of the window trying to make sure the front tire was positioned okay while pulling in.