Gaseous Fire Suppression System


Fire Suppression Systems


With today's demands on IT infrastructure, protection against collateral damage is paramount! Ask yourself, is your IT facility adequately protected against fire? The heat generated from the latest server technology is enormous, the potential for fire is higher now than anytime before, with powerful rack servers stacked on top of each other with serious heat outputs.


This article will give you the low down on fire suppression technology, with an unbiased view to the PRO’s and CON’s of the main types of fire suppression options.


What makes a fire suppression system work?


Standards and Codes of Practice


Fire suppression systems should be installed to at least the NFPA, ISO14520, BS6266 and BS5839 codes of practice for fire detection and fire suppression systems. Smoke detection in high airflow environments should be installed as per the recommendations of the BS6266 standard. This standard advises on the number of detectors required based on velocity of the high air flow, this is crucial for high airflow in this type of environment.


The Mechanical elements of a fire suppression systems, namely the fire suppression cylinders and delivery pipe work should conform to the ISO14520 standard. In addition to this, a theoretical demonstration of the flow performance should be demonstrated with use of the OEM’s flow modelling software. With all fire suppression systems, the design should be approved to ensure that the pipe runs are not obstructed and can be practically installed without adding elbows and other pipe work accessories to avoid any other obstacles such as light fittings, duct work, etc.


Smoke Detection Principles


A fire suppression system, must comprise of at least two fire zones and at least two smoke detectors. Traditionally a mix of Ionisation smoke detectors and Optical (Photoelectric) smoke detectors were used to detect a wider range of smoke particles. Today the optical technology covers this and provides more stability of than that of ionisation detectors, particularly in high airflow streams.


Alternatively, enhanced fire detection can be achieved with the use of VESDA air sampling systems. Using VESDA smoke detection can provide conclusive detection with accurate testing and measurement principles. Interrogation can also be achieved by looking at extensive event logging, which will paint a picture of events occurring prior to a fire suppression discharge!

Operation


The fire suppression system uses two modes:


MANUAL FIRE SUPPRESSION MODE : This is based on Human intervention, the operation of a gas release call point or manual actuator will discharge the fire suppression agent. The Fire Suppression system will not deploy the system automatically.


AUTOMATIC FIRE SUPPRESSION MODE : Two zones or two devices are needed to prove a coincidence. This coincidence is confirmation that there is smoke present and the fire suppression system will deploy the fire suppression agent. The delay from the first stage alarm (first detector activated) to the second stage alarm is variable, depending on how fast the detectors are responding. Once the second detector is activated that system normally incorporates a 30 second delay from alarm to fire suppression release!


The Environment that the Fire Suppression system is being used


Most fire suppression systems are only as good as the enclosure they are used in. It is vitally important to ensure that the protected enclosure can maintain the fire suppression agent at the highest level of equipment for 10 minutes following a discharge. Why do we do this? The fire suppression system is a fire ‘suppression’ system NOT an extinguishing fire system. Re-ignition will occur should the fire suppression concentration be reduced or if the fire suppression agent escapes/leaks out of the protected enclosure.

Room Integrity


To evaluate this, the fire suppression installer must carry out a Room Integrity Test. A room integrity test proves fire suppression retention capability of the room. The test procedure compares positive and negative pressurisation against flow. This calculates the accumulative aperture (this is a sum of all openings in the protected inclosure).


The room integrity test calculates that rate at which the gas will leak from the protected space. In simple terms, the best way of describing this is, imagine a fish tank of water filled to the very top, the very top being the room height. The tallest piece in the fish tank is like the tallest piece of equipment in the computer room. The fire suppression agent is the water! Now imagine that there where small holes in the tank, this is holes in the protected space. As the water (fire suppression agent) leaks out of the tank/enclosure, the tallest piece of equipment will eventually be exposed to air. If this occurs within 10 minutes, then essentially the room will fail the test. If the water (fire suppression agent) leaked at a slower rate, leaving the tallest piece of equipment covered longer than 10 minutes, then the room will pass the integrity test.


Why do we use ten minutes as the datum? The ISO1450 and NFP2001 deem this period as a minimum period to allow human intervention, such as the fire brigade to deal with the problem without the risk of allowing the fire to spread and do more damage!


With this in mind choosing the correct fire suppression agent is critical.

Summary Of Fire Suppression Agent


Inert Gas Fire Suppression


Naturally occurring Gases often used as blends, these blends are used to reduce oxygen to below 15% and above 12%. Oxygen levels below 15% will not allow a fire to burn as the oxygen is simply not there to fuel the fire. Levels of Oxygen between 12% and 15% is adequate to sustain human life. Oxygen levels between 12% and 10% will show visible signs of effects asphyxiation Oxygen levels below 10% are extremely dangerous. This type of fire suppression is considered a green option and does have many advantages used in the right application. Inert Gas Fire Suppressions are commonly found with the following blends and names:-


Inergen fire suppression - IG541


A Blend of Nitrogen, Argon and small percentage of CO2. This fire suppression blend is made up of 50% Argon, 42% Nitrogen and 8% Co2. What makes this fire suppression system unique? The mix of Co2 into the blend helps a humans absorbation of oxygen in a depleted oxygen environment. Co2 also increases the heart rate and induces hyper ventilation so that the body breathes in more than normal! On the flip side the disadvantage of IG541 fire suppression comes with contaminated air with bi-products of combustion that are breathed in with the intensified inhalation.


Argonite fire suppression - IG55


This is a blend of 50% Argon & 50% Blend of Nitrogen. The fire suppression gas is blended to offer better buoyancy for the fire suppression agent keeping the fire suppression gas at higher levels in the protected enclosure for longer!


I3 Fire Suppression - IG55


This fire suppression system is the same as above, however, it uses regulated valves to reduce the pressure shock when the fire suppression system is initially deployed! Again this system is a blend of 50% Nitrogen and 50% Argon. By reducing the initial pressure shock with the fire suppression generates in the first 10 seconds of discharge, the required number pressure relief vents are reduced.


Argon Fire Suppression system - IG05


This is not as common these days, but is a simple and effective solution. Argon is heavier than air and used as a single compound is makes this fire suppression system easier and cheaper to refill. The disadvantage of this fire suppression system is the weight of the gas which reduces the hold time.


Synthetic Gaseous Fire Suppression


Compounds and blends of man made chemicals to form a fire suppression agent. The method of extinguishing is basically like a coolant, this to attacks the free radicals of the heat make up in a fire. This type of fire suppression absorbs heat which suppresses the fire. Synthetic fire suppression uses small concentrations by volume which offers practicality and ease of installation, they are normally cheaper than the inert alternatives. We will list two types only, there are more, but all operate in the same way.

FM200 Fire Suppression - HFC227


This fire suppression agent has concentrations are set at 7.9% by volume for the room and ceiling voids and 8.5% by volume for the floor void. Concentrations levels higher than 10% are dangerous. FM200 fire suppression is an HFC. HFC’s (hydrofluorocarbon: a fluorocarbon emitted as a by-product of industrial manufacturing) have been banned by the Kyoto Protocol, but HFC’s used for the use of fire suppression systems have been excluded. There is no certainty that HFC’s will not be banned for the use of fire suppression in times to come, but for now there is no banned imposed on HFC227 (FM200). Advantages of FM200 Fire Suppression are:- Cost, ease of installation and it is safe to use in occupied spaces. The floor space required for the fire suppression cylinders is minimal. Disadvantages are that is much heavier than air and the room that it is being used in must be adequately sealed. The FM200 fire suppression agent has an atmospheric lifetime of 36 years and as a result will contribute to global warming if discharge/released!


Novec 1230 Fire Suppression - 1,1,1,2,2,4,5,5,5-NONAFLUORO-4- (TRIFLUOROMETHYL)-3-PENTANONE


This fire suppression agent in NOT an HFC. It is essentially derived from an cleaning material manufactured by 3M. The concentrations of this fire suppression agent is 5.3% by volume! Novec 1230 fire suppression works by reducing heat in the same way of FM200! The fire suppression agent is an extremely versatile agent! The advantages of Novec 1230 Fire Suppression are, installation is simple. The floor space required for the fire suppression cylinders is minimal and the refilling can be done on site! The Novec 1230 fire suppression agent is much heavier than air and requires a good room seal to be in place. The cost of the agent is almost twice that of FM200!

Water Mist Fire Suppression


This is a simple but effective fire suppression solution. Water misting fire suppression solutions work only when the heat is sufficient to draw in the micro particles of water. As the heat intensifies, air is drawn into the fuel/heat mixture and so grown the fire. This fire suppression induces water into this heat mix and the fire is cooled and suppressed. Water mist fire suppression has limited uses and is not suitable for IT infrastructures or in applications which will be harmed by the reformed water.


Dry Powder Fire Suppression


This is effective and works by discharging a blanket of inert powder. The dry powder fire suppression does not fit all applications and is limited to specific application which are not suitable for the fire suppression systems listed above


Oxygen Reduction Fire Suppression


A novel way of keeping a protected enclosures oxygen levels below 15% at all times. This eliminates the risk of ignition due to the constant low levels of oxygen. Effective in large warehouses where other fire suppression systems become too large and too cumbersome to install!


CO2 Fire Suppression


Out of all fire suppression systems, CO2 is the most effective at killing a fire but this includes humans too. It is not a suitable fire suppression agent for occupied spaces. CO2 cools the fire and removes the oxygen. CO2 systems are commonly used for local applications, they can also be used for total flooding, but stringent precautions must be used if this is the preferred fire suppression agent!

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