Is it safe to use a propane torch bought at a Hardware store?
Propane and butane are pure alkanes. They don't produce anything nasty when burned. The worst you could possibly get should be carbon monoxide (and I am not even sure it can be produced in a torch, the dioxide ifs much more likely), but it being a gas, it won't stick to your food. The complex molecules you get from heating the food itself have more potential for being harmful than the combustion products of a propane butane torch. Ago yes, it is food safe. 

Another matter of safety is that it is easier to cause a fire with a hardware store torch, because it has more power than the kitchen ones. But a sensible adult should be able to handle the thing safely.