Chlorine demand in wastewater is due to algae, bacteria, iron, manganese, hydrogen sulfide, COD, BOD, etc. The selection of a gas chlorinator is dependent upon the flow rate of water to be treated, and the chlorine demand of the water. Chlorine gas is supplied in steel cylinders, as a compressed gas in a liquid state. The pressure in the cylinder is dependent upon the temperature of the cylinder. As a safety feature, the cylinders are fitted with fusible plugs that will melt at about specific temperature. This is done to prevent the cylinder from exploding if it is in a fire situation.