Suppression

Automatic fire suppression

Automatic fire suppression systems control and extinguish fires without human intervention.

According to the National Fire Protection Association, there were 1,602,000 fires reported in the United States in 2005. There were 3,675 civilian deaths, 17,925 civilian injuries, and $9.2 billion in property damage. A fire department responded to a fire every 20 seconds and a structure fire was reported every 62 seconds.

Although man has fought fire for centuries, it was not until Feb. 10, 1863 that the first fire extinguisher patent was issued to Alanson Crane of Virginia. The first fire sprinkler system was patented by H.W. Pratt in 1872. But the first practical automatic sprinkler system was invented in 1874 by Henry S. Parmalee of New Haven, CT. He installed the system in a piano factory he owned.

The Society of Fire Protection Engineers was founded in Boston on Oct. 31, 1950,

Types of automatic systems

Automatic system in a computer room

Today there are numerous types of Automatic Fire Suppression Systems. Systems are as diverse as the many applications. In general, however, Automatic Fire Suppression Systems fall into two categories. These are engineered and pre-engineered systems.

Engineered Fire Suppression Systems are design specific. Engineered systems are usually for larger installations where the system is designed for the particular application. Examples include marine and land vehicle applications, computer clean rooms, public and private buildings, industrial paint lines, dip tanks and electrical switch rooms.

Pre-Engineered Fire Suppression Systems do not require the involvement of a design engineer beyond the original product design. Pre-engineered systems are comprised of pre-designed components. Examples of pre-engineered systems include commercial kitchen systems and industrial paint rooms and paint booths and industrial storage areas.

Pre-engineered systems most commonly use a simple wet or dry chemical agent, such as potassium carbonate or monoammonium phosphate (MAP). Engineered systems use a number of gaseous or solid agents. Many are specifically formulated. Some, such as 3M Novec 1230 Fire Protection Fluid, are stored as a liquid and discharged as a gas.

Components

By definition, an automatic fire suppression system can operate without human intervention. To do so it must possess a means of detection, actuation and delivery.

In many systems, detection is accomplished by mechanical or electrical means. Mechanical detection uses fusible-link or thermo-bulb detectors. These detectors are designed to separate at a specific temperature and release tension on a release mechanism. Electrical detection uses heat detectors equipped with self-restoring, normally-open contacts which close when a predetermined temperature is reached.

Remote and local manual operation is also possible.

Delivery is accomplished by means of piping and nozzles. Nozzle design is specific to the agent used and coverage desired.

Extinguishing agents

In the early days, water was the exclusive fire suppression agent. Although still used today, water has limitations. Most notably, its liquid and conductive properties can cause as much property damage as fire itself.

Agent	Primary Ingredient	Applications
FM-200	Heptafluoropropane	Electronics, medical equipment, production equipment, libraries, data centers, medical record rooms, server rooms, oil pumping stations, engine compartments, telecommunications rooms, switch rooms, engine and machinery spaces, pump rooms, control rooms
3M Novec 1230 Fire Protection Fluid	Fluorinated ketone	Electronics, medical equipment, production equipment, libraries, data centers, medical record rooms, server rooms, oil pumping stations, engine compartments, telecommunications rooms, switch rooms, engine and machinery spaces, pump rooms, control rooms
Argonite	Argon and nitrogen	Same applications and FM-200 and Novec 1230 fluid; less Class B style hazards
FE-13	Fluoroform	Police evidence freezers, inerting natural gas pumping stations or trains/trucks/cranes operating in cold weather, electronics, medical equipment, production equipment, libraries, data centers, medical record rooms, server rooms, oil pumping stations, engine compartments, telecommunications rooms, switch rooms, engine and machinery spaces, pump rooms, control rooms
Wet Chemical	Potassium carbonate	Commercial kitchens
ABC Dry Chemical	Monoammonium phosphate	Paint booths, dip tanks, coating operations, flammable liquid storage areas, paint mixing areas, exhaust ducts
Regular Dry Chemical	Sodium bicarbonate	Gasoline, propane and solvents, live electrical equipment, flammable liquids
Carbon Dioxide	Carbon Dioxide	Non-occupied control rooms, coating operations, paint lines, dust collectors, transformer vaults, live electrical equipment, flammable liquids, commercial fryers
Foam	Synthetic detergent, polysaccharide, fluoroakyl suffaccant	Flammable liquids
Purple K Dry Chemical	Potassium bicarbonate	High hazard commercial and industrial applications, especially with flammable liquids
Halotron 1	2,2-dichloro-1,1,1-trifluoroethane	Live electrical equipment, flammable liquids
Water Mist	Water	Ordinary flammables (Paper, wood, cloth)
Water	Water	Ordinary flammables (Paper, wood, cloth)

Health and environmental concerns

Despite their effectiveness, chemical fire extinguishing agents are not without disadvantages. In the early 20th century, carbon tetrachloride was extensively used as a dry cleaning solvent, a refrigerant and as a fire extinguishing agent. In time, it was found carbon tetrachloride could lead to severe health affects.

From the mid 1960s Halon 1301 was the industry standard for protecting high value assets from the threat of fire. Halon 1301 had many benefits as a fire suppression agent; it is fast acting, safe for assets and required minimal storage space. Halon 1301s major drawbacks are that it depletes atmospheric ozone and is potentially harmful to humans.

Since 1987, some 191 nations have signed The Montreal Protocol on Substances That Deplete the Ozone Layer. The Protocol is an international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion. Among these were halogenated hydrocarbons often used in fire suppression. As a result manufacturers have focused on alternatives to halogenated hydrocarbons, such as Halon 1301 and Halon 1211.

A number of countries have also taken steps to mandate the removal of installed Halon systems. Most notably these include Germany and Australia, the first two countries in the world to require this action. In both of these countries complete removal of installed Halon systems has been completed except for a very few essential use applications. The European Union is currently undergoing a similar mandated removal of installed Halon systems.

Modern systems

Since the early 1990s manufacturers have successfully developed safe and effective Halon alternatives. These include DuPont FM-200, American Pacific’s Halotron and 3M Novec 1230 Fire Protection Fluid. Generally, the Halon replacement agents available today fall into two broad categories, in-kind (gaseous extinguishing agents) or not in-kind (alternative technologies). In-kind gaseous agents generally fall into two further categories, Halocarbons and Inert Gases. Not in-kind alternatives include such options as water mist or the use of early warning smoke detection systems.

Gaseous fire suppression

Gaseous fire suppression is a term to describe the use of inert gases and chemical agents to extinguish a fire. The system typically consists of the agent, agent storage containers, agent release valves, fire detectors, fire detection system (wiring control panel, actuation signaling), agent delivery piping, and agent dispersion nozzles. Less typically, the agent may be delivered by means of solid propellant gas generators that produce either inert or chemically active gas.

Theory

There are four means used by the agents to extinguish a fire. They act on the "fire tetrahedron":

Reduction or isolation of fuel

No agents currently use this as the primary means of fire suppression.

Reduction of heat

Representative agents: Novec 1230.

Reduction or isolation of oxygen

Representative agents: Argonite / IG-55, carbon dioxide, Inergen, and NN100.

Inhibiting the chain reaction of the above components

Representative agents: FE-13, FE-227, FE-241, FE-25, FE-36, FM-200, Halons, Halon 1301, Freon 13T1, NAF P-IV, NAF S-III, and Triodide (Trifluoroiodomethane).

Application

Broadly speaking, there are two methods for applying an extinguishing agent: total flooding and local application.

Systems working on a total flooding principle apply an extinguishing agent to a three dimensional enclosed space in order to achieve a concentration of the agent (volume percent of the agent in air) adequate to extinguish the fire. These types of systems may be operated automatically by detection and related controls or manually by the operation of a system actuator.

Systems working on a local application principle apply an extinguishing agent directly onto a fire (usually a two dimensional area), or into the three dimensional region immediately surrounding the substance or object on fire. The main difference in local application from total flooding design is the absence of physical barriers enclosing the fire space.

In the context of automatic extinguishing systems, local application does normally not refer to the use of manually operated wheeled or portable fire extinguishers, although the nature of the agent delivery is similar.

Safety precautions

Systems using certain agents, such as carbon dioxide, in enclosed spaces present a risk of suffocation. Numerous incidents have occurred where individuals in these spaces have been killed by carbon dioxide agent release. To prevent such occurrences, additional life safety systems are typically installed with a warning alarm that precedes the agent release. The warning, usually an aural and visible alert, advises the immediate evacuation of the enclosed space. After a preset time, the agent starts to discharge. Accidents have also occurred during maintenance of these systems, so proper safety precautions must be taken beforehand.