Just use water. The illusion will still be there if you use a authentic(and clean) gas can.
Yes, authenticity is a a pleasantly refreshing feeling. I love authenticity in haunted attractions.Thanks for the thoughts... we always tread a very fine line (overstep, in some cases). The authenticity seems to be the main attraction - we've had 3 people quite literally wet their pants, 1 group of guests escorted off the premises and 1 person break down in floods of tears - but all of them rebooked for following years! It's a tricky balance - I guess that ultimately, they know we would break character if anyone got into serious trouble. Please be assured we take care of people though