Residential Fire Suppression Systems - Assignment Example

Student Name: xxxxx Tutor: xxxxxx Title: Residential Fire Suppression Systems Date: xxxx ©2016 Table of Contents Table of Figures 3 1.Introduction 1 2.Residential Water mist System 2 2.1Components 3 2.2Operation 4 2.3Design criteria 5 2.4.1 Advantages 6 2.4.2 Disadvantages 6 3. Residential Sprinkler System 8 3.1Components 8 3.2Operation 9 3.3Design criteria 10 3.4.1Advantages 10 3.4.2Disadvantages 11 4. References 11 Table of Figures Figure 1: Illustration of a Water mist fire Suppression System (Source: Tyco(TM) Aquamist) 2 Figure 2: Prototype Residential Sprinkler (Sourced from Tyco Fire and Building Products) 8 1. Introduction Open plan is a generic term used in architectural and interior design for any floor plan which makes use of large, open spaces and minimizes the use of small, enclosed rooms as private offices. Open planning has the advantage that the occupants will be aware of the presence of fire quickly, as it offers any impediment to the spread of smoke. When an unprotected corridor is enclosed by partitions, those partitions provide some defense against the spread of smoke in the early stages of the fire, despite having no fire resistance rating [The10]. The company intends to service a number of flats through a single staircase and an unprotected extended common corridor of 25m. This is more than the recommended escape distance of 7.5m provided in Approved Document B. however, in order to protect the safety of the occupants, as well as provide them with sufficient time to escape the building in case of a fire outbreak, the company intends to install a mechanical smoke extract system coupled with a residential water spraying system. This water spraying system is intended to extinguish common household fires, usually flammable liquid fires, or to provide cooling to an exposed area likely to be subject to intense heat radiation from a neighbouring fire. This is to prevent wanton spread of fire in the building providing life safety and asset protection to the occupants. This is important as recent studies have shown that many victims of fire outbreaks are very vulnerable, such as sleeping people, the elderly, pre- schoolers, handicapped or those impaired by drugs or alcohol [Bry07]. This paper focuses on the main components, key design criteria, operation and the pros and cons of a residential water mist system and residential sprinkler system to provide the company with enough information to make a choice on the most appropriate system for the building. 2. Residential Water mist System A water mist system is a fixed fire protection system, comprising of components for automatic detection and actuation, water supply delivery and water atomization systems. The water is discharged as a spray of small droplets [Wil06]. Over 1,000 water mist suppression systems have been installed in the UK in the recent past as a compensatory measure to the meet the provisions and regulations specified in the ADB. Water mist fire suppression systems have demonstrated relative efficiency in suppressing various types of fire, with the added advantages of no toxins or environmental pollution. They have also been found to be effective in the protection of spaces onboard ships, life safety building applications and protection of assets, such as electronic equipment and machinery spaces. Recently, they have been considered for use in residential buildings for fire suppression [Liu04]. Figure 1: Illustration of a Water mist fire Suppression System (Source: Tyco(TM) Aquamist) 2.1 Components The components of the water mist suppression systems that facilitate their operation include; 1. Fire fighting medium – The medium commonly used for fire suppression is water, which works by removing the heat of ignition of the fuel. Additives, such as antifreeze and inert gases, may be added to the water to increase its suppression efficiency to different types of fire, especially where plain water may not be sufficient, such as Class B and C fires. 2. Detection system – For the water mist system to be activated, there needs to be a system that will detect the outbreak of a fire. Smoke/ heat detectors and actuators and automatic quick response glass bulb nozzles are generally used to detect fires, with an alarm system to warn the occupants of the impending danger. 3. Atomization system – This reduces the stream of water into a spray of small droplets for easy dispersion. This is done with the aid of nozzles and orifices, filters and strainers to achieve the mist state. The system may be single fluid or twin fluid depending on the type of fire to be suppressed. The pressure of the atomization is dependent on the area the mist is required to cover, with pressures ranging from low (), medium () to high () 4. Delivery system – The atomized water particles need to be transmitted to the area of the fire, as well as to means of escape to prevent the fire from engulfing these regions. The water may be delivered using wet/ dry pipe, pre- action or deluge systems. The material used to make the pipes should be free from corrosion to prevent malfunctioning of the system, as this could have dire consequences. Common materials used are stainless steel, fire rates CPVC1 plastic or copper pipes. 5. Supply system – The fire fighting medium needs to be readily available for use in the case of a fire outbreak. This can be achieved by the use of storage tanks installed in the buildings, active connection to town mains and standby pumps to provide water from off-site locations. In residential buildings, most of the water mist systems used will be low pressure, wet pipe systems, with automatic smoke/ heat detector systems supplied by storage tanks containing potable water installed in the building. Quick response glass bulb nozzles may be used for more affluent neighbourhoods or in an office setup where there’s a lot of sensitive material that would be damaged or lost in the event of a fire. 2.2 Operation At operation, a cone of spray containing the atomized water particles is discharged by the system to fill the protected zone with water mist. Inert gases and other additives may also be included to supplement the action of the water when required. The system should be able to generate, distribute and maintain a sufficient concentration of small droplets for the effective suppression of fire risk in order to meet the objective for fire protection [Wil06]. The main considerations for the system to provide the required fire support are; a. Maintaining the correct pressure/ flow characteristics at the discharge nozzle for a duration sufficient to suppress the fire b. Optimal placement of nozzles in the structure to ensure maximum coverage of space, and minimal water wastage due to collisions of the water spray with solid surfaces such as structural elements or components installed by the occupants. c. Shutting down of natural airflows through ventilation systems, in order to minimize loss of water mist from the protected area2. Water mist systems cannot be used in isolation to protect the building, but come as part of a package with other systems that complement its operation, such as, fire detection systems in the form of smoke or heat alarms to trigger their operation. Passive fire protection may also be necessary to reduce the effective area the water mist system will require to act upon. 2.3 Design criteria 1. Fire control mechanisms When the heat sensitive quick response glass bulb detects the fire outbreak, the fire is usually at a relatively developed stage and appropriate for water mist control. Other response systems such as smoke and heat sensors may take even longer to detect the fire, meaning that the actuation of the water mist system should be immediate. The water droplets then penetrate the fire. The water mist suppresses the fire either by reducing the temperature of the fuel below its ignition point, reducing the radiative heat of the fire to prevent ignition of surrounding surfaces, and to reduce the oxygen concentration in the zone the of interaction with the fire. This cools the hot fire gases and smoke, as well as wetting other potential combustible fuels, effectively protecting the other parts of the room/ building from further spread of the fire. 2. Fire control objective This is the function the water mist system will be installed to perform. It affects the type of equipment the company will be required to install, which is subject to cost and maintenance operations. It may be; a. Fire extinguishment – the complete elimination of a flaming or smouldering fire by a sharp reduction in the heat release rate. b. Fire suppression control – a steady reduction in the heat release rate of the fire to achieve a lower level of burning by limiting the growth of the fire, thus protecting the structure. 3. Duration of water mist protection The ADB does not provide guidelines on the standard duration for which water mist should be applied, and it is up to the discretion of the company. However, in order to ensure sufficient suppression of the fire, there are minimum recommended durations of application (using BS 9251 sprinkler systems); a. Domestic – >10 minutes b. Residential – 30 minutes The minimum time may be extended in special cases, especially in areas where people may be sleeping, as more time is required for evacuation, or if there are few people to handle the spread of the fire. The company may consider the use of specialized sensors which detect when the heat levels fall below dangerous levels, and allow a small duration before the water mist system is stopped. This may be suited for the fire control objective systems. 2.4.1 Advantages 1. Water mist systems use less water than sprinkler systems 2. They produce less water damage as the pressure at the nozzles can be controlled 3. They do not always require a water mains connection 4. They are cheaper in terms of systems weight 2.4.2 Disadvantages Water mist systems have the following shortcomings; 1. Not effective for all kinds of fire Deep seated fires will take longer to extinguish as the water mist does not extinguish fires primarily by wetting of solid fuels. Small fires and shielded fires also present challenges as the spray of mist cannot cover them in sufficient quantity. 2. There is no reference data of their effectiveness, thus cannot be installed in residential and domestic applications 3. The small orifices may be susceptible to blockage by impurities in water, causing malfunction 3. Residential Sprinkler System A fire sprinkler systems is an active fire protection method which provides adequate pressure and flowrate to a distribution piping system, with sprinklers connected. Sprinkler systems have often been installed in schools, office buildings and factories for a long time now. However, the installation in residential buildings has not been the norm [USF08]. [The10] specifies that sprinklers should be provided for flats exceeding 30m in height. Despite the fact that the building in question is only 25m, the length of the common corridor, which exceeds the required limit necessitates the use of a sprinkler system to handle fire outbreaks. Figure 2: Prototype Residential Sprinkler (Sourced from Tyco Fire and Building Products) 3.1 Components The components for the sprinkler system are [BSI05]; 1. Sprinklers – they may be upright, sidewall or concealed types, suitable for residential applications. Only new sprinklers should be used and they should be fitted with a quick response thermal sensitivity rating. 2. Pipes and fittings – the transmission of water can be done in stainless steel, copper or plastic pipes. Fittings to metal pipes should be joined by soldering or brazing to ensure there’s no leakage or pressure damage. 3. Detection system - Smoke/ heat detectors and actuators and automatic quick response glass bulb nozzles are generally used to detect fires, coupled with an alarm system to warn the occupants of the impending danger. 4. Firefighting medium – The medium commonly used for fire suppression is water, which works by removing the heat of ignition of the fuel. Additives, such as antifreeze and inert gases, may be added to the water to increase its suppression efficiency to different types of fire, especially where plain water may not be sufficient, such as Class B and C fires. 5. Supply system – The firefighting medium needs to be readily available for use in the case of a fire outbreak. This can be achieved by the use of storage tanks installed in the buildings, active connection to town mains and standby pumps to provide water from off-site locations. 3.2 Operation Each sprinkler is connected to a network of pipes that supply water and it has a smoke/ heat sensor which activates that specific sprinkler only. This means that when the heat from the fire reaches the activation temperature of the sprinkler, only that sprinkler will direct water to the source of energy. This allows the system to control the fire without unnecessary discharge of water [SFP08]. A heat- sensitive glass bulb holds each sprinkler head closed, applying pressure to a pipe cap which acts as a plug to prevent water from flowing until the ambient temperature around the sprinkler is higher than the design activation temperature of that sprinkler. Therefore, only one or two sprinklers may be activated, maximizing the pressure over the point of origin of the fire and minimizing water damage to the building [PDR09]. The average pressure of a sprinkler system causes less damage as compared to a firehose. 3.3 Design criteria 1. Fire control mechanisms When the heat sensitive quick response glass bulb detects the fire outbreak, the fire is usually at a relatively developed stage and sprinkling is required. The sprinkler system suppresses the fire primarily by wetting the fuel. This has the effect of reducing the temperature below the heat of ignition of the fuel. This cools the hot fire gases and smoke, as well as wetting other potential combustible fuels. 2. Fire control objective Sprinkler systems are generally installed for complete fire extinguishment. The amount of water supplied at the head, coupled with the pressure ensure that the conditions are unfavourable for further fire spread. Sprinkler systems are used where the spread of fire needs to be curtailed immediately, and the contents of the building are not overly- sensitive to water damage. 3. Duration of sprinkler application For a single storey building spanning less than in floor area, the minimum volume permitted should be the water demand rate for two sprinklers times 7 minutes [Bry07]. Considerations to the total floor area, as well as the total height of the structure should be made to determine the most efficient duration for sprinkler application. 3.4.1 Advantages 1. Residential sprinkler systems will be smaller in size as compared to industrial ones due to the reduced area. 2. They have a low water requirement which can be adequately supplied by storage tanks 3.4.2 Disadvantages 1. The pressure requirements for efficient fire suppression are relatively high 2. For larger establishments, there is need for connection to town mains 4. References The10: , (The Building Regulations, 2010), Bry07: , (Bryan, 2007), Wil06: , (Williams & Jackman, 2006), Liu04: , (Liu, et al., 2004), USF08: , (U.S. Fire Administration, 2008), BSI05: , (BSI, 2005), SFP08: , (SFPE, 2008), PDR09: , (PDR&MD, 2009), Read More