Our Services - Fire Suppression
Fire Suppression Systems Sometimes we forget how important it is to have a suitable extinguishing system available until an accident occurs. Modern kitchens (amongst other critical function services) present a dangerous combination of high amounts of flammable oils and extreme sources of heat, creating an environment in which fire is a constant threat. As well, extraction hoods capture a large amount of grease that deposits in the interior of the hoods, the fans and ducts, providing possible ways to initiate or propagate a fire.What makes a fire suppression system work? Standards and Codes of Practice Fire suppression systems should be installed to at least the 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. 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. |
