The weight can be a real issue too. Swinging around that saw gets real old in a hurry, not to mention the fumes/exhaust the engine gives off, those aren't good for ANYBODY.
The bar is thin enough to do some major damage/injury to people and property when you get to swinging it around. That first injury, and the lawsuit that comes with it, will be for more than your haunt will make for many years combined, not to mention that you won't be able to get insurance or permits to carry on.
Consider using fiber-optics sprouting from the bar, and pipe in the sounds of the chainsaws surrounding the guests. The surround-sound will disorient the guests as to where they are being attacked from, adding to the element of surprise, and the fiber optics (think fine fishing line) sprouting from the bar will appear to be sparks without the chance of fire or burns. Using a little tech light @ 5000 lumens or so, will give you a light weight but solid light source for the fiber optics, and it gives you an inexpensive way to get your effect. They use a 18650 battery, which can be recharged, so you can always have your effect of "sparks" at the touch of a button.