Another gas which potentially could be used in lieu of Nitrogen and Argon and that would still be safer then propane would be R 134A refrigerant. I don't believe that it would be nearly as flammable and it does not contain any oxygen in and of itself. It is available at most auto parts stores, Walmart etc. However, I would not discharge it inside an inhabited space, nor for that matter would I discharge propane under those same conditions. When I weigh the value of my A** to a little wasted developer the "apples and oranges" comparison becomes very apparent. But, hey, it's your deal...your mileage may vary.