Automatic fire suppression refers to a system designed to either completely put out a building fire or confine it to a limited space without the need for immediate human oversight and control. Standard automatic fire suppression systems utilize a connected series of smoke and fire detectors, along with ceiling-mounted water sprinkler systems to isolate and contain fires. Special cases where water would do irreparable damage to equipment, such as in computer server rooms or offices that rely on computer networks, often employ an automatic fire suppression system that uses inert gasses. This gaseous fire suppression method puts out a fire by starving it of the oxygen that it needs to burn fuel such as wood and synthetic furnishings.
The fire sprinkler system is identified as the most standard type of automatic fire suppression system, and has been deployed in US businesses as long ago as 1874. Estimates as of 2010 show that it has produced significant benefits both in terms of saved lives and reduced property damage as opposed to waiting for a fire department to arrive to extinguish a fire. Statistics show that wet pipe sprinklers worked properly 96% of the time and reduced death rates from fires by 83%, as well as property damage by at least 40%. Where sprinkler systems have failed to do their job, it has most often been due to the fact that the building in which they were being installed was still under construction, or because 53% of the time they had been deliberately shut off when a fire wasn't expected.
The two most frequently used types of automatic fire suppression systems are wet pipe sprinklers and dry pipe sprinklers. While both look similar externally, wet pipe sprinklers are pipes that are constantly filled with water under pressure that can be released immediately when a fire is detected. They outnumber dry pipe sprinklers by a factor of 10 to 1 and account for 73% of all fire suppression systems.
Dry pipe sprinklers are considered effective fire suppression methods in the US only 79% of the time, and are based on a design where the sprinkler piping is initially composed of compressed air or nitrogen gas. This is due to the fact that dry pipe systems exist in areas where the year-round temperature periodically drops below the freezing point of water, or because the building its built to protect does not see routine human habitation, such as in warehouses and storage depots. A dry pipe system still uses water to suppress the fire, but the gas must first be evacuated from the pipe by water pressure before it is effective.
Another type of water-based automatic fire suppression is the water mist or condensed aerosol fire suppression system. Instead of spraying a stream of water, it sprays a mist that covers a wide surface area as it vaporizes to steam and quickly dilutes the oxygen content in the room. It also reduces heat levels and acts similarly to fogging systems that firefighters use, with the advantage that it causes less water damage and can protect large areas for which inert gas systems are often used.
Chemical fire suppression systems for sensitive electronic equipment used to rely on such inert gasses as halon and carbon dioxide to remove oxygen from a room and extinguish the fire. Both of these chemical suppressants have been discontinued for different reasons. Halon is known to be a powerful ozone-depleting gas, and it was internationally banned for fire suppression at the beginning of 1994. Carbon dioxide has been discontinued for effects similar to that of halon, in that anyone trapped in a room when the system went on would be asphyxiated and killed by the lack of oxygen present. Replacement compounds for these chemicals include INERGEN®, composed mostly of nitrogen and argon, and FM-200®, or heptafluoropropane, which comply with standards that require at least 12% of the concentration of gas in a room to be composed of oxygen while they are in operation.