The Building Environment: Active and Passive Control Systems - Assignment Example

Name Course Date Table of Contents Name 1 Course 1 Date 1 Table of Contents 2 Residential sprinkler system 3 Design requirements 4 Types of fire sprinklers systems 5 Design objectives 6 Advantages of residential sprinkler systems 7 Disadvantages 7 Residential Water Mist System 8 Design criteria 8 The fire control mechanisms 9 Fire control objective 9 Duration of protection of water mist 10 Protection of fire fighting access and the means of escape 10 Technology 10 Advantages of water mist sprinklers 11 Disadvantages 12 References 13 Residential sprinkler system Residential sprinkler systems are automatic sprinkler systems used in residential premises and are designed, installed and maintained according to the British Standard BS 9251. It is a combination of overhead and underground piping which is installed throughout the building and is connected to an automatic water supply. The system detects and controls the residential fires and therefore provides protection against the loss of life, injury and damage to property. If the system is installed as designed in accordance to the residential standards, it is expected to prevent the fire from reaching flashover, thus improves the opportunity of the occupants to escape (Li & Baker, 2012). Due to the complexity related to different aspects of sprinkler system design and installation, various terms have been defined in NFPA 13. This was meant to establish uniformity and consistency. The main term, sprinkler system is defined as a combination of overhead and underground piping connected a water supply. The piping is design hydraulically with the piping system located overhead in the building. Sprinklers are attached the overhead piping are connected systematically and are attached to sprinklers. Valves that control each riser are located on the supply piping. Heat detection mechanism activates the system so that it can discharge water over the fire area. When the system starts operating, an alarm is actuated by a device located on the system riser (Cote & NFPA, 2003). Various components that comprise a sprinklers system are shown in the figure below. Figure 1: Various sources of water supply and attached system attached to sprinkler system (Cote & NFPA, 2003) That rules that address private fire service mains, water storage tank and fire pumps are found in NFPA 20, 22 and 23. The system response faster to fire and has a unique water distribution pattern. The sprinklers are required to have more uniform distribution pattern because residential fire often depends on one sprinkler per room, unlike in standard sprinklers which produce overlapping patterns in order to cover up for the voids. Residential sprinklers are also required to wet furnishings including sofas and the periphery location of the room. Design requirements The escape travel distance is prescribed in order to minimize the time taken by the occupants to reach an exit. The escape travel distance can be extended by installing automatic sprinklers as one of the considerations. The reason is that sprinklers can be able to suppress the fire growth and maintain the conditions that are tenable for the occupants to exit safely than if the sprinklers were not installed. This technique allows more time for escape and thus is it allowed to travel longer to an exit. According BS 9991:2011, the maximum travel distance for escape to the stairs, in a building fitted with sprinklers system, in a single direction may be increased from 7.5m to 15m, but fro escape in at least two directions, the travel distance may be increased from 30 to 60m. Residential sprinkler system should not be used as a compensatory measure to allow extended travel distances along the corridor. BS 9991:2011 also allows an open plan if the sprinklers are fitted throughout the building with three storey. But this should also be in conjunction with fire resistant doors and partitions (British Standards Institution, 2011). 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 In addition, according to the requirement, an open plan flat design is not suitable for buildings with single stairs on internal entrance. Types of fire sprinklers systems There are two types of sprinklers systems available. They include wet pipe system and dry pipe systems. Wet type system is installed in places where there no likely to be freezing. The pipes are permanently filled with water, and have constant supply of water available in case of fire. The system reacts quickly to fire and is the most common type installed in buildings. When fire occurs and produces sufficient heat that is able to activate the sprinklers. The system also requires low maintenance and is cost efficient (Bradshaw, 2006, 402). Figure 2: Basic components of wet pipe sprinkler system (Cote & NFPA, 2003). Dry pipe system- In this system, the pipes is filled with air and water is allowed to flow after air has escaped. As a result, the water discharge will delay, which is suitable for buildings in areas where the temperature is below 40C, so that water does not freeze ion the pipes. The sprinkler system is fitted with fast opening mechanism to allow air move out and hasten the flow of water. The type is more reliable and less costly to maintain, but it operates slowly (Bradshaw, 2006, 402). Figure 3: Dry pipe system (Cote & NFPA, 2003) Design objectives Residential sprinklers normally designed to control fire, but some sprinklers allows fire suppression. The sprinklers control fire by limiting the fire size by pre-wetting nearby combustible materials and reducing the rate of heat release, but at the same time marinating the gas temperature at the ceiling in order to prevent structure damage. It can also suppress fire by reducing the heat release rate to the point where there will no fire regrowth after applying large water quantities by fire plume on the surface of the burning fuel. The figure below shows the graphical representation of fire control and suppression in terms of the rate of heat release as a function of time. Figure 4: analogy of fire suppression/control (Cote & NFPA, 2003) The main objective of residential sprinklers is life safety. The sprinklers are intended to maintain tenable conditions in the room of fire origin. The sprinklers systems that are designed according to NFPA 13D are meant to avoid flashover in the room of fire origin and to increase the possibility of the building occupants escaping or being evacuated safely (Giesler, 2011, 196). Advantages of residential sprinkler systems The system is recognized in European and UK standards It can last for long compared to mist systems The components are manufactured independently It less costly to install compared to water mists system They can be used to put off slow burning fires Disadvantages It requires large amount of water to extinguish fire Large pipes are used It cannot be used in areas with small spaces Residential Water Mist System Like residential sprinkler systems, water mist systems have fire detection system, water supply, distribution network and a discharging water mechanism (spray for residential sprinkler systems and mist for water mist system). There is no UK or European standard that covers water mists systems in residential buildings, and this has led to the growing concerns that the some systems may not perform as intended. In contrast to sprinklers system, water mist systems are specific to the project, and each occupancy or potential risk need a unique design. Thus, it is not possible to design the system by referring to one of the various standards like in sprinkler systems where BS 9251 or BS EN 12845 are used to design and produced full compliant system (British Standards Institution, 2011). This system consists of a water supply that is connected to piping systems which are connected to automatic nozzles. When water mist is operated, it discharges a cone of spray that contains small droplets of water which cover the protected area with water mist. For the water mist system to be effective, it should produce, distribute and sustain the concentration of droplets that can be able to control fire long enough to meet the objective of the protection. The main activities performed in order to achieve this include: Maintain the flow or pressure at the nozzle for a long time The nozzles should be able to have full coverage of space and minimum wastage of water because of the collision of the water droplets on surfaces. It may also require shutting down the airs flows through ventilation systems to reduce the loss of water mist from the protected area (British Standards Institution, 2011). Design criteria The detail about the criteria through which the system design is based on is provided. They include the following. The fire control mechanisms The objective of fire control The duration of protection The fire control mechanisms In case of a fire incident, a detector, which can be a glass bulb that is sensitive to heat, response quickly and actuate the water mist system. The system is likely to be actuated when the fire has already establish in the residential premises and suitable for water mist control. Water mist system uses fine water sprays to extinguish or control by cooling the fire plume and the flame, attenuation of radiant heat and displacement of oxygen by water vapour. It also minimizes the potential fire spread by cooling the smoke and fire gases, and wetting of the combustible fuels within the fire zone. Water mist usually uses less amount of water at relatively higher pressure in comparison to the residential sprinkler systems (Madrzykowski, 2002). The spacing between the nozzles of the water mist systems are smaller than the residential sprinklers spacing, thus more nozzles are required to provide fire protection for a particular area. Thus, water mist systems can provide the same levels of fire protection in relation to residential sprinkler systems, but at a relatively higher cost (Madrzykowski, 2002). Due to the fact that water mists system is not meant to extinguish fire by directly wetting the fuels, it has less impact on deep seated fires. The system is not also effective in extinguishing shielded fires and small fires. Fire control objective The objectives of fire control for water mist system include the following; Fire control/suppression – This is reduction of heat release rate which results in control of fire growth and protection of structure through cooling the fire gases, and the objects by pre-wetting combustible materials. Fire extinguishment – this is a sharp reduction in the rate of heat release that results in complete elimination of shouldering fire or flame. The objective must be stated by the contractor together with supporting evidence, in order for the authorities to assess risks and interactions with other residential premises protection systems. Duration of protection of water mist Although there is no standard prescription of the least time for the water supply, minimum duration should be selected for every project. The minimum values for the duration of water supply for automatic sprinkler systems can be used. For example, BS 9251 requires sprinkler systems for residential premises to have a minimum duration of 30 minutes or 60 minutes for BS 5306 or BS EN 12845. Residential water mist system may be used as an alternative to residential sprinkler system and it usually gets conditional approval. For water mist to be accepted by authorities for residential buildings, the design should be based on appropriate standards, performance tests and fire demonstration to ensure that the system meet the objective (British Standards Institution, 2011). Due to extended corridors and other factors such as the presence of old people, the state of the people (as they may be asleep or they may be drunk or under the influence of drugs), it is important to increase the time duration for water mist protection and install detectors with high sensitivity.  Protection of fire fighting access and the means of escape There are some issues that need to be considered and addressed in this system that are installed in compensation to meet the building regulatory requirements. They include the following: Extent of fire control/ suppression Time needed for fire-fighting access The tenability conditions in the premises The likely scenario after the exhaustion of the water mist The time needed for the escape of the premises occupants Technology Water mist system typically uses compressed gas at pressure between 150 and 1000 psi. The propellant controls the formation of mist and expels it through the nozzles and a suitable rate to fro complete dispersal. Low pressure water mist is more effective and is less costly. Water mist systems falls into one of the two groups High pressure Low pressure Head pressure is usually greater than 35 Bar. The pressure for cylinder based system is normally 200 to 300 bar. The pipework has small bore, stainless and has 12mm – 30 mm. It can either have stored water in tanks and high pressure cylinders or high pressure pumps The maintenance schedule is similar to residential sprinkler systems but close attention is given to the maintenance of nozzles to ensure that they are not blocked If the filters are prevent, the stored water can be supplement with tank systems The cylinder based system cannot the water supplies with other fire protection that uses water The nominal water density is normally 1 – 2 lpm/m3 Dry and wet systems are available The head pressure is usually 5 to 10 bar but not more than 12. The pipework is usually 20 to 65 mm and can be made of copper or steel. It usually uses electric pumps and stored water. The maintenance schedule is similar to residential sprinkler systems but close attention is given to the maintenance of nozzles to ensure that they are not blocked The stored water supply can be supplement by pumping in depending on the available connections. The system can share the water supply with other fire protection systems that uses water (whereas in residential sprinkler system, the design would not comply with BS EB 12845. The nominal water flux density is between 2 and 3.5 lpm/m3. Dry and wet systems are available Advantages of water mist sprinklers This system uses a relatively smaller amount water to fight fires. This is beneficial considering the cost of installation and the reduced amount of water used. Mist system also has a potential to be used in locations that are too small to accommodate big water tanks and pump equipment similar to that of residential sprinkler systems. The system is lighter compared to the residential systems Smaller pipes are used (Moran & Wiley, 2003) Disadvantages It entails high cost of maintenance Very high quality of water is needed to be used by this system They are less effective at extinguishing slow burning and deep seated fires compared to residential sprinkler system. The system has short run time; it usually run for 10 minutes. References Bradshaw, V. (2006). The Building Environment: Active and Passive Control Systems. Hoboken: John Wiley & Sons. British Standards Institution. (2011). Fire safety in the design, management and use of residential buildings - code of practice. London: BSI, British Standards Institution. 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. Giesler, M. P. (2011). Fire and life safety educator. Clifton Park, NY: Delmar Cengage Learning. Hurley, M. J. (2016). SFPE handbook of fire protection engineering, New York: Springer. 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. Li, G., & Baker, S. P. (2012). Injury research: Theories, methods, and approaches. New York: Springer. Moran M. J. & Wiley, (2003). Introduction to thermal systems engineering: thermodynamics, fluid mechanics, and heat transfer, Volume 1: Introduction to Thermal Systems Engineering: Thermodynamics, Fluid Mechanics, and Heat Transfer, Read More