Chlorine is a dangerous chemical that can lead to burn injuries if not used properly. This is especially true for indoor pools with poor ventilation. There, chlorine in the water evaporates into the air - becoming chlorine gas - and gets trapped in the room, unable to escape and becoming more and more concentrated. This can lead to uncomfortable chemical burns throughout your respiratory tract, as well as in your eyes and on your skin. Chlorine must be used in moderate amounts in the swimming pool.