Fire Suppression

Fire Suppression Systems

The need for fire suppression systems

Fire suppression systemWith the growth of the computer age and sensitive electrical equipment, equipment of critical importance to companies and assets of high value, business and insurance companies are concerned about the effects a fire would have on such vital assets. In a high percentage of cases, a business would not survive a fire.

One way many companies are choosing to avoid such a catastrophe is to have a Gaseous or also known as a Clean agent fire suppression system installed. You may be asking, what is a “Fire Suppression System”? Well, the simplified explanation would be; a fire suppression system is a very large fire extinguisher that can be automatically activated on sensing any smoke within the protected area. However, this explanation is in a very simple form and there is a lot more involved in an operational system.

The system will have automatic detectors situated throughout the protected area into zones that cascade. The strategy of the extinguisher system is to detect smoke at an early stage via the fire alarm control panel and extinguish the fire before it has a chance to develop into a full blown fire. The detectors send a signal to the control panel to initiate the gas discharge into the protected areas through a network of pipe work and nozzles.

There are two forms of extinguishant agents used in Gaseous suppression systems, you have an inert gas that is able to extinguishant the fire by reducing the oxygen within the are being protected to a level low enough that the combustion cannot be maintained. The extinguishant is stored in cylinders at a pressure of 150-300 bar. The other type of gas is chemical based and extinguishes a fire by reducing the heat and the temperature of the fire. The pressure in the cylinders of a chemical based system is lower than that of an inert system.

Detection, Control System and Actuation

Kentec fire supressionThis part of the suppression system focuses on detecting fire at an early stage, once detected the information is transmitted to the fire alarm control panel. The detection can be in the form of your standard smoke detectors, and this can be conventional or addressable, or an air sampling system detector is used to give a very early warning of smoke particles. In a typical computer room layout, the ceiling and floor voids would also be protected with detection. The type of detector used would be Ionisation and optical, to give the system the best chance to detect early, any type of smoke, whether it be smouldering or clearer smoke with smaller particles. The detectors are in a cascade format and zoned to provide a first and second stage operation. Detection in computer suites is to conform to BS6266.

The fire control panel is mounted outside the protected area usually by the entrance door and has a key switch facility to enable the user to switch the system between automatic and manual. The fire alarm control panel can be of a conventional type or addressable. Over the last 6 years or so, you will find that addressable fire alarm control panels are more commonplace. Kentec and Advance Electronics are the leaders providing fire suppression control equipment.

Extract, A separate smoke extract system should be installed to remove the gas and the products of combustion from the protected area, following a discharge. Where possible the duct work should do straight to an outside wall without passing through any other areas, furthermore, the extract system should not be part of the main building ventilation system. Within the protected area, the intake extract vent should be at low level and the outlet vent at high level. The operation of the extract system can be from a control switch at the front of the panel, or it can be an individual switch, labelled “Smoke Extract”.

Extinguishant Storage and Distribution

fire suppression cylindersThe next main component within a fire suppression system is the distribution and storage for the extinguishant gas or liquid. The agent is stored in cylinders under pressure and connected to a network of pipes that are terminated within each area or zone by discharge nozzles. The nozzles can have a spray range of 180 degrees or 360 degrees, depending upon their location.

Where possible the cylinders should be located outside the protected area for ease of maintenance and testing without having to access the protected zone. Inert gas storage is at a higher pressure than its chemical counterpart, and therefore this allows the cylinders to be stored at a further distance away from the area it is protecting, this can be as far as a hundred meters or more. In contrast, the cylinders for chemical systems have to be very close to the protected area, due to pipe work friction losses.

Operation

Fire suppressionThe basic operation of the system involves two stages, called “First stage” and “Second Stage”. The purpose of the two stages is to prepare the room for a possible gas discharge and to alert personnel of an early warning of smoke giving them time to investigate and perhaps resolve the issue that may have activated the smoke detection. In addition, it avoids accidental gas discharge that can occur if a detector were to get contaminated due to dirt, or water mist that can be discharged from a faulty air conditioning unit.

The term giving within the fire alarm detection side of the system is called “double knock” or a “Coincidence”. A fire suppression Addressable fire alarm panel, provides the best form of coincidence, as the effects can be archived within the programming features of panel, rather than having to wire the detectors in a specific format as required with a conventional panel. Kentec Electronics, Advance Electronics and C-TEC produce some of the most advance system equipment in this field. .

First Stage Alarm

fire suppression 1st stageOn detection of smoke from the smoke detectors or air sampling system, the fire alarm control panel should alert the occupants and personnel responsible for the room, with a bell and Xenon Beacon. In addition, shut down any air conditioning or ventilation services within the protected area. If fire dampers are installed to isolate the protected area, the dampers should also closed at this stage.

A first stage activation will give users time to assess the nature of the alarm and take reasonable measures to tackle the fire manually if appropriate, or to investigate if the activation is a false alarm. Investigation of such an alarm should be carried out by personnel who are deemed competent. If the situation warrants entry into the protected area, it would be wise to set the system to manual operation.

Second Stage Alarm

Following the activation of the first detector to initiate first stage, an activation of a second detector on a different zone would cause the system to go into second stage alarm. At this point, a different audible sound is activated and a different colour xenon beacon, the change in audible tone and xenon beacon colour is alerting staff that the system is going to discharge the extinguishant.

In addition, the activation of the pre-discharge timer will commence. After this time has elapsed, the extinguishant is discharged into the protected area. The fire suppression system would be interfaced to the main fire detection system serving the main building. This will alert the occupiers of the main building of the situation and if connected to a monitoring centre, it will call the fire brigade.

There was a time that the second stage alarm was connected to a company’s computer shutdown system; however, over time, this practice is not so common, due to the disruption that occurred to the business, during the shutdown period and the fact the no notice is given.

Extract

A separate smoke extract system should be installed to remove the gas and the products of combustion from the protected area, following a discharge. Where possible the duct work should do straight to an outside wall without passing through any other areas, furthermore, the extract system should not be part of the main building ventilation system.

Within the protected area, the intake extract vent should be at low level and the outlet vent at high level. The operation of the extract system can be from a control switch at the front of the panel, or it can be an individual switch, labelled “Smoke Extract”.

 

Integrity Testing

It is essential that a fire protection system operates correctly and to the specification it was designed to. To do this, adequate containment of the extinguishant within the fire risk area is essential and it is therefore a requirement that integrity testing is carried out on a regular, if not on a minimum annual, basis.

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Gas Extract

A separate extract system should be provided to remove the extinguishant after discharge. In the event of a fire, it may also need to remove the products of combustion as well as decomposition products that may be present with halocarbon gases.

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Inert v Chemical

The Advantages and Disadvantages of: Chemical Systems (FM200/NOVEC/CO2) v Inert Systems (i3/Inergen)

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