On a realistic note I think Jason is right BUT what I believe you are side stepping jason is the fact that YES, if you are in a AFV and a flamethrower would blast the tank, breathing would be impossible, if not VERY VERY terrible. So maybe they were not used in such a manner BUT if they COULD, the effects would be decent. Just the danger, speed, weight, ect ect of carrying one limits it from being used as a pure assault weapon.