Fire Detection and Suppression

Fire can be one of the most damaging physical events. Damage to systems, buildings, and people can cost a company great deals and be a tragedy. Because of this it's very important that fire safety be taken seriously. It's also why regulations exist that ensure a minimum amount of protection against fire. This post will discuss the different technologies used for fire detection and suppression. Equally important is fire prevention which includes proper training and ensuring the correct supplies are accessible in case of emergency, though this will not be discussed.

Fire detection

Fire detection systems come in two base varieties, manual and automatic. Manual systems are the red pull boxes that many people are familiar with. These systems are activated by a person once a fire is detected. Automatic systems are able to sense heat or smoke in a variety of ways. When a fire is detected the system will sound an alarm before triggering a suppression system.

A common type of smoke detector uses a photoelectric device to test the air for smoke. In one variety, a beam of light originates at an emitter and ends at a receiver. The system monitors the intensity of the light and sounds an alarm if the light becomes obscured. Another variety draws in air surrounding the detector and tests the air quality with a photoelectric device.

Heat activated systems monitor the temperature of the environment and watch for noticeable changes. These systems can be set to sound an alarm if a certain temperature is reached (fixed temperature) or if the rate of change exceeds a predefined limit (rate-of-rise). Rate-of-rise systems can provide an earlier alarm than fixed temperature systems but can also be the source of more false alarms.

It is important that fire detection devices be installed in all the proper areas and not just in obvious places like offices and hallways. Many office buildings have dropped ceilings and raised floors where wiring is ran. There should be detection devices installed in both of these to ensure an early alert in case of an emergency. Additionally, smoke or heat can often gather in ventilation systems before being dispersed to the surrounding areas, so there should be detection devices installed in these areas as well.

Fire suppression

Not all fire is equal. There are four types of fire and each requires a certain type of suppression device. Use the wrong one, and you could end up making the fire bigger/stronger rather than extinguishing it. The table below summarizes the classes of fire and the appropriate suppression method.

Fire Class	Type of Fire	Elements of Fire	Suppression Method
A	Common combustible	Wood products, paper, and laminates	Water, foam
B	Liquid	Petroleum products and coolants	Gas, CO₂, foam, dry powders
C	Electrical	Electrical equipment and wires	Gas, CO₂, dry powders
D	Combustible metals	Magnesium, sodium, potassium	Dry powder

Foams are mainly water-based and are designed to float on top of a fire and prevent any oxygen from flowing to it. Gas, such as halon or FM-200, mixes with the fire to extinguish it and is not harmful to computer equipment. Halon has been found to damage the atmosphere, however, and is no longer produced. CO₂ gas removes the oxygen from the air to suppress the fire. It is important that if CO₂ is used there be an adequate warning time before disbursement. Because it removes the oxygen from the air it could potentially endanger people's lives. CO₂ is often used in unmanned facilities for this reason. Dry powders include sodium or potassium bicarbonate, calcium carbonate, or monoammonium phosphate. The first three interrupt the combustion of a fire, and monoammonium phosphate melts at a low temperature and smothers the fire.

Water sprinkler systems are much simpler to install than any of the above systems but can cause damage to computer and electrical systems. It's important that an organization recognize which areas require which types of suppression systems. If water is to be used in an environment that contains electrical components, it's important that the electricity be shut off first. Systems can be configured to shut off all electrical equipment before water is released. There are four main types of water systems:

• Wet pipe - Wet pipe systems always contain water within the pipe and are usually controlled by a temperature sensor. Disadvantages of these systems include that the water in the pipe may freeze, and damage to the pipe or nozzle could result in extensive water damage.
• Dry pipe - Dry pipe systems employ a reservoir to hold the water before deployment, leaving the pipes empty. When a temperature sensor detects a fire, water will be released to fill the pipes. This type of system is best for cold climates where freezing temperatures are an issue.
• Preaction - Preaction systems operate similarly to dry pipe systems but add an extra step. When empty, the pipes are filled with pressurized air. If pressure is lost, water will fill the pipes, but not be dispersed. There is a thermal-fusible link on the nozzle that must first melt away before the water can be released. The advantage of this system is it gives people more time to react to false alarms and small fires. It is much more effective to put out a small fire with a hand-held extinguisher than a full spray system.
• Deluge - Deluge systems have their sprinkler heads turned all the way open so that greater amounts of water can be released at once. These types of systems are not usually used in data centers because of this.