Humidity Humidity Humidity is the amount of water vapour present in air. Water vapour, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. The amount of water vapour needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or losing water mass. The amount of water vapour contained within a parcel of air can vary significantly. For example, a parcel of air near saturation may contain 28 grams of
Air pressurized water Air pressurized water Air pressurized water (APW) extinguishers are a type of fire extinguisher that use ordinary water (HO) to suppress fire. The water is propelled by ordinary air (atmosphere), pressurized in the extinguisher. They are also known by the slang term "water can". Although only effective on Class A fires, they have the advantages of being inexpensive to build and maintain, and leaving no special chemical residue when used. A standard APW extinguisher in the United States contains of water in a stainless steel tank. The water is discharged by means of a ½-inch hose, with a smooth-bore nozzle