As I mentioned earlier, they don't really work for firefighting. They only filter the ambient air before delivering it, which can expose the user to anything that filter isn't designed for. There's no filter that works for everything--you pick different ones based on what you'll encounter, which doesn't work in an environment where you don't know the hazard. I don't know for sure, but I also think they don't have any way of compensating for high ambient temperatures.