Residential Fire Sprinkler Systems - Assignment Example

Name Course Date Table of Contents Name 1 Course 1 Date 1 Table of Contents 2 Residential fire sprinkler systems 3 Wet pipe sprinklers system 5 Dry fire sprinkler systems 5 Design specifications 6 Residential Water Mist System 8 Design specifications 8 Working principle 8 Fire control mechanisms 9 Fire control objective 9 Means of escape 10 The main components 11 Advantages of water mist system 12 Disadvantages of water mist system 13 Conclusion 13 References 14 Residential fire sprinkler systems Residential fire sprinkler systems is an automatic fire sprinkler system that has quick response automatic sprinkler heads made for low water pressures and low heat release (International Association of Fire Chiefs, 2016). The sprinklers automatically detect and suppress, extinguish or control fires. It is expected that if the sprinklers are design and installed as recommended, it will control early warning systems as well as control fire. The sprinklers reduce the production of smoke and heat and delay fire to allow the building occupants to escape. They have ability to put off fire at an early stage of development, which is very critical in fire protection. When they are activated, they put off fire in the affect area and not other part of the building (Garrett & British Standards Institution, 2008). The installation of sprinklers in residential building will result in considerable savings in terms of building construction costs, improved level of property protection, enable flexibility of building design and enhance the levels of occupant safety. However, the main objective of sprinklers in residential building is to provide life safety protection for the occupants. They are designed to suppress or control fire that may occur to allow time for the building occupants to move to safety. They are designed to deliver water to the location of fire origin in order to suppress, control or extinguish fire, pre-wetting the surrounding structure and materials. The system protection continues for 30 minutes. The property is also protected by minimizing the damage at the room of fire origin (Bafsa, 2011). This report discusses the design requirements and the benefits of incorporating residential sprinkler system and water mist systems in a given design. It assists the stakeholders in determining the best approach to use in order to comply with the building regulations. It also considers how cost savings can be achieved. The sprinklers provide fast response to the fire incident as the sprinkler heads are strategically located, and when they are activated by heat, they automatically put off the fire within a short time after it starts. Since the sprinkler heads located at a point near fire operates, small amount of water is needed compared to normal fire fighting. Residential sprinklers provide the following benefits. There will be less fire damage to the building It provides a quick response that limits fire to the location of origin Minimize the risk of loss of life or injury due to fire There will be less water damage to the building (Garrett & British Standards Institution, 2008) The source of water for residential sprinklers can be from bonds, the city water mains or from storage water. Different water supply methods can be adopted in these systems. One of the systems is direct connections to the mains water using one supply for domestic services and for fire sparkler systems. This connection is shown in the figure below. Figure 1: Direct connection system using pipe for both domestic water and sprinkler systems The alarms and the valves monitors and control the water flow, and the distribution pipes carry water to fire sprinkler heads from water source and increase the water pressure. Current systems detect fires and discharge water before the fire grows into unmanageable or catastrophic conditions, thus reducing the deaths. Residential sprinkler systems are designed, installed and maintained according to the British Standard BS 9251. Residential sprinklers are divided wet pipe sprinkler systems and dry pipe sprinkler systems. NFPS 13D and 13R standards provide the guidelines for the installation of both types of residential sprinklers. However, they are only limited to a maximum of two storey buildings. The two types of sprinklers are discussed below. Wet pipe sprinklers system They are the most popular systems as they use less number of components and short in time compared to other systems. They have automatic fire sprinklers connected to pipes distributed regularly, filled with water from the main riser and under pressure all the time. They cannot be installed in places where the pipes are exposed to low temperatures, below 400F, as the water can freeze in the pipes making the systems to be inefficient. The system has minimal maintenance, hence results in financial saving. They are the most reliable systems and require less maintenance. In addition, the water flows immediately after fire detection (Giesler, 2011). The operation of this system depends on the heat reaction by the head of fire sprinkler. When fire occurs, a metallic heat sensor or fusible glass bulb in the head of the sprinkler melt or shatters and separate. Either of the action results in water discharge through the piping and water sprays over fire in an engineered pattern. Wet pipe systems are activated if the temperature is between 1550F and 2850. Dry fire sprinkler systems These are sprinkler systems which are installed in places where the temperature is low like the parking garages or unheated buildings. These fire sprinkler systems have compressed air that is supplied by electric air compressor (Giesler, 2011). Dry pipe fire sprinkler systems alarm port and a valve clapper that is held closed by the pressure gradient between water pressure and air pressure at the valve interface. They also have pressure switches that can be used to maintain or regulate the pressure in the systems. Air is discharged after the sprinkler had is fused by heat. This allows the valve clapper to open and water flows into the system. Although these systems are slower compared to wet pipe systems, it is beneficial in areas where there is the risk freezing in the pipes (Giesler, 2011, 194). Design specifications Installation of sprinklers is recognized as alternative for extended travel distances in the corridors. British Standard BS 9251 and BS 9991 provide the criteria for installation of residential sprinkler systems. When a building is fitted with sprinklers, the travel distance to the exit routes should be kept at 7.5 m to 15m in one direction and 30m to 60m when there is more than one direction. NFPA 13 provides guidelines for the installation and protection of fire protection systems. The following principles are applied. Wet pipe system should be fitted with listed water flow automatic alarm Dry pipe systems should have listed alarm attachment BS 9991 allow the use of open flats if they are fitted with sprinklers systems throughout the building and installed according to BS 9251 or BS EN 12845, and the fire alarm should be installed according to BS 5839-6. But the limits set out for open flat designs include: The open flat should be less than 12m x 16m in size. The minimum ceiling height in buildings with open flats should not exceed 2.25m. Open flats are situated on single level The travel distance in a residential building should 7.5m in one direction and 30m if the escape routes are in two directions. BS 9991 allows a maximum dead end travel distance of 15m if the sprinkler protection is installed in all apartments. Figure 2: The maximum travel distance to the exit The advantages of residential sprinkler systems over water mist systems include the following: They are recognized as European and UK standards They have long systems life (over 30 years) There performance is based on a third party thorough testing procedure and approval of equipment and installers They are reliable as they have been tried and tested for several years. Their components are produced independently, has no lock –in They last longer than water mist system thus allow more time for escape. The systems have high water discharge, thus they are very reliable. The disadvantages include: They consume more space as they require large pipes. They use large amount of water compared to water mist system They cannot be installed in places with limited space Residential Water Mist System Water mist systems are fixed fire protection systems which utilize water to suppress, control or extinguish fire. The systems consist of automatic nozzles heads connected to a distributed network of piping system filled with water with high pressure. Water mist system operates by discharging a cone of spray that contains water droplets which fill the protected zone with water mist. In some cases, additives are added into the systems to enhance protection (Williams et al 2006). The system generates, distributes and continues produce water mists that is sufficient to fire risk for enough time to meet the objectives of the protection. The system also works under low pressure of below 12.5 bar (175 psi) or over 35 bar (500 psi) for high pressure systems. NFPA defines water mist as water spray whose droplets diameter is less than 1000 microns at maximum pressure of operation. The sizes of the droplets can be varied by changing the pressure through the nozzle. In order to achieve the objectives the following should be done: The correct pressure must be maintained for sufficient amount of time Careful positioning of the nozzles to minimize water wastage and to cover the space fully Design specifications The required minimum duration for the design systems should be selected depending on the project as there is currently no standardized value. The values for automatic sprinkler systems can be used. For BS 9251 sprinkler systems, the minimum duration for residential buildings is 30 minutes and 50 minutes for BS EN 12845 sprinkler systems. Working principle Unlike sprinkler system which fights fire by wetting or cooling the surfaces of the materials, water mist system works with a different principle due to the sizes of the droplets. When the droplets enter the fire zone, there is rapid heat exchange which converts the droplets into steam and cools the fire. The steam also displace oxygen that surrounds the fire, thus assist in extinguishing fire (British Standards Institution, 2011). Water mist system design shown state the fire control mechanism, the fire control objectives and the time duration of water mist protection as discussed below. Fire control mechanisms Heat sensitive glass bulb is used to actuate the water mist system. Thus, the actuation may occur when the fire will be well established. Then the water mist system discharges the water droplets which penetrate into the fire (Madrzykowski, 2002). It attacks two elements of fire triangle: heat and oxygen. It means that it combines traditional sprinkler system and gas suppression effect. It removes oxygen from the system and cools the fire. Figure 3: Water mists attacks two elements of fire triangle (Semco fire protection) The objective is to minimize the radiative heat, temperature and oxygen the within the compartment of fire origin. The rest of the compartment is protected by smoke fumes and fire (British Standards Institution, 2011). Fire control objective Since the objectives of fire control for water mists system include: Extinguish class A and class B fire types. Control temperatures in the room to avoid flashover and fire spread to neighbouring rooms Provide an alternative to residential sprinkler systems design constraints with similar level of fire safety (Cote & National Fire Protection Association, 2003) Early activation of the suppression systems will reduce HRR, otherwise the fire enters into rapid growth stage where it may become overwhelming and the suppression systems will not work. The figure below shows the effect of suppression system in HRR. Figure 4: Suppression on heat release rate (Maevski et al., 2011) The system can be able to detect small fire with the magnitude of 1MW to 5 MW. Means of escape The main aspects that are considered when installing water mists systems as a compensatory feature to meet the specifications of the building regulations include the following: Time needed for the building occupants to exit the building. The conditions in the compartment should remain tenable for a minimum time period to enable the egress of the occupants. The time needed before the arrival of fire fighters. There should be enough time for fire fighting and rescue services to arrive and perform the rescue operations. The conditions after fire protection by water mists The coverage of the fire protection system. Tenability limits in the building (British Standards Institution, 2011; Hurley, 2016). The main components Although the water mist systems available in the market are not standardized compared to automatic sprinkler systems, they can be categorized into the following components: Fire fighting medium- water with additive or antifreeze Detection – glass bulb nozzles for automatic response. They detect and actuate the system and can provide alarms Atomization – these is performed by fluid system, strainers and filters, orifice and nozzle, and pressure which can be below 12.5 bar (low pressure system), between 12.5 bar and 35 bar (medium pressure), or can be above 35 bar (high pressure). Delivery system – this can be dry pipe system or wet pipe system. Supply – can be from the mains supply, storage vessel like cylinders or tanks, pumps and propellant (Williams et al 2006). The common type of water mist systems in residential buildings is wet pipe systems with low pressure, fast response glass nozzles with water supplied from tanks. The residential building water mist system with the tank and pump is arranged as shown below. Figure 5: The layout for water mist system for residential building (Williams et al 2006) Advantages of water mist system The advantages of water mist sprinklers include: When the systems are used as a compensatory feature, it may have indirect cost reduction because of design changes. They require less water and thus economical when considering the amount of water needed or the installation of large tanks They are used in places where the space is limited as they use smaller pipes and smaller tanks compared to residential sprinkler systems The systems are lighter and is economical when weight is considered It is not necessary to use water mains connection They produce less water damage compared to sprinklers systems (Williams et al 2006) Disadvantages of water mist system The disadvantages include the following: The systems can run for a short time compared to residential sprinkler systems. It usually run for approximately 10 minutes There are no European, UK or international standards for designing the systems for domestic residential applications There performance can be affected by ventilation systems The system is costly if the cost of installation and provision of water as well as the costs of testing, inspection and system maintenance is considered. They require the use of expensive stainless steel pipe work They require very high quality water as it can be easily be blocked of small orifices. They are not effective in extinguishing fires that are deep seated or which are slow burning (Williams et al 2006) Conclusion Water mist system can control can be used successfully to control and suppress fire for different design scenarios. The system has a potential to replace sprinkler system. However the system does not remove insoluble toxic gasses like carbon dioxide which is produced in the interior building fires. Water mist systems can provide fire protection just like sprinkler systems. The difference is that in water mist system, use compressed air or high pressure pumps as a medium for atomization as the water moves out through the nozzle. References Garrett, R. H., & British Standards Institution. (2008). Hot and cold water supply. Chichester, West Sussex, U.K: Wiley-Blackwell. International Association of Fire Chiefs. (2016). Fire investigator: Principles and practice to NFPA 921 & 1033, Burlington, MA: Jones & Bartlett Learning Bafsa, (2011). Using Sprinkler Systems in Buildings and Structures, Compliance with current fire safety guidance, Technical Guidance Note No 2, Issue No 1: October 2011 Giesler, M. P. (2011). Fire and life safety educator. Clifton Park, NY, Delmar Cengage Learning. Williams C., Jackman L. and Principal Consultants, BRE, (2006). An independent guide on water mist systems for residential buildings, Building Research Establishment. Cote, A. E., & National Fire Protection Association. (2003). Operation of fire protection systems: A special edition of the Fire Protection Handbook. Quincy, Mass: National Fire Protection Association. Madrzykowski, D., Fleming, R. P., United States., United States Fire Administration., & National Institute of Standards and Technology (U.S.). (2002). Review of residential sprinkler systems: Research and standards. Gaithersburg, MD: U.S. Dept. of Commerce, Technology Administration, National Institute of Standards and Technology. Maevski, I. Y., National Research Council (U.S.)., National Cooperative Highway Research Program., American Association of State Highway and Transportation Officials., & United Semco fire protection, High-Pressure Water Mist System, The intelligent use of water, Semco States. (2011). Design fires in road tunnels. Washington, D.C: Transportation Research Board. Hurley, M. J. (2016). SFPE handbook of fire protection engineering, New York: Springer. Read More