You don't need brake fluid, any organic (hyrdo-carbon) fuel will work. What happens is the Chlorine reacts with something in the fluid (I think it's the water, but I'm no expert). Anyway, the reaction builds heat and pressure to the point that your fuel (brake fluid in this case) catches fire. This isn't a really smart thing to carry when trying to survive though. Chlorine has very few survival uses to humans, and under the right circumstances is extremely toxic and deadly.