I nearly murdered myself using this method last winter. I had just spent my Home Depot gift card on a little heater, and decided the first task would be to tidy up some greasy junkyard parts, using some chlorine-infused brake cleaner. The overspray from the brake cleaner made its way into the heater, and badaboom, gas attack. I've never coughed so violently! I had to vacate the garage, and let it air out. Naturally I learned my lesson, so I only gassed myself one more time that night.
The sad part is that I was entirely sober. My lungs hurt for a week. Learning is fun!