If you are carrying any amount of chlorine gas, you must stop at every railroad crossing and be extra cautious about proceeding across. A chlorine spill from a collision with a train could be highly dangerous. Chlorine gas is poisonous. (If you're transporting chlorine in cargo tanks, you must have a gas mask with you in the cab.) Chlorine is also a strong oxidizing agent. It can react with flammable materials and start fires. The resulting fires can spread corrosive or toxic gases.