“A water curtain system uses an array of spray nozzles to create a barrier of water to contain a fire inside a small area. The nozzles can be mounted to shoot water either upwards or downwards. The goal of a water curtain is to provide exposure protection or to stop the flow of flammable vapors from migration into a hazardous area.”
Reference: Center for Chemical Process Safety, Guidelines for Engineering Design for Process Safety, 2nd Edition, 2012
Comment: water curtains are effective by dispersing and diluting a flammable and/or toxic cloud quicker. Several cases can be distinguished depending on the molecular weight of the gas relative to air and the solubility in water. Evaporating initially cold heavy cryogenic gas shall be lifted quickly by heating it up and giving it momentum upwards. Heavy gases can be dispersed and ignition prevented by a deluge system. Clouds of in water soluble gases such as chlorine and ammonia will be effectively diluted by a water curtain.