Sprinkler Systems and Their Use in the Design for Life Safety - Term Paper Example

FIRE PROTECTION ENGINEERING Critical assessment of sprinkler systems and their use in design for life safety and property protection purposes 1. Sprinkler Systems 1.1 Sprinkler System A sprinkler system is typically a device installed within buildings to detect a fire in its early stages. The main idea in the development of sprinkler systems is to protect property but recently they have been used for life safety as aid to the means of escape of people from a burning building. Generally, sprinkler system consists of water supply with control valves and pipes fitted with sprinkler heads. These sprinkler heads are fitted in strategic locations below the ceiling. It operates in certain temperature determined from the ambient temperature condition of the place in which they are to be installed. In the United Kingdom, more than 60% of fires are controlled by sprinkler systems (Snow, 2003, p.4). Worldwide, a number of reports show that significant number of people survived a fire because of effective sprinkler system. For instance, the National Fire Protection Association of NFPA 2007 report shows there are lower death rate per fire and lower damage to property in buildings fitted with sprinklers (House of Commons, 2009, p.23). Statistics in Australia shows that out of 9,022 fires in sprinklered buildings, 99.5% were controlled or limited by sprinklers (Snow, 2003, p.4). Installing fire sprinkler systems in buildings have a number of benefits, these include 24 hours, and 365 days protection from fire, savings in compartmentation construction, reduced insurance premium, and others (Snow, 2003, p.4). However, the principal benefits are undoubtedly the potential reduction in losses from fires and probability of fire and improved life safety due to significant reduction in probability of death or injury from fire (US Fire Administration, 1989, p.5). Since sprinklers operate directly over a fire, smoke, toxic gases, and reduced visibility do not affect their operation. Moreover, since sprinkler heads are strategically located and only those fused by the heat of fire operate, less water is consumed to put out a fire (American Water Works, 2008, p.40). The value of automatic sprinkler protection according to Cote (2003), is not only the sharp reduction in property loss but life safety benefits coming from diminishing treat to building occupants by warning people and putting out the fire at its early stage. For instance, sprinkler systems enable extended travel distances, reduced ratings required in wall assemblies and interior finish materials (p.301). 1.2 Sprinkler as Life-Safety Systems The main functions of sprinkler are to detect a fire at its early stage and distribute water on the fire area in order to extinguish or limit fire spread. A sprinkler is considered life-safety systems and in BS EN 12845, it is defined as an integral part of measures required to protect life (DOH, 2007, p.6). The Approved Document B for Fire Safety in Buildings Volume 2 emphasized the reduction of risk to life if sprinkler systems are installed in buildings. It can be installed as a compensatory feature in order to address a particular risk or throughout the building to ensure protection. However, design and installation of sprinkler systems must comply with either BS 9251:2005 Sprinkler systems for residential and domestic occupancies and BS DD 252 for specification and test. For non-residential buildings, installation should comply with the requirements of BS 5306-2:1990 and BS EN 12845:2004 (Approved Document B, 2007, p.11). Residential fire sprinkler systems are often automatic and equipped with fast response sprinkler heads (see discussion in the next section) designed for low heat release and low water pressures. The difference between commercial and residential fire sprinklers is that residential types have smaller piping and thinner heat sensitive elements. Smaller piping is used because water requirement in residential buildings is small while thinner heat sensors enable rapid heat collection and faster activation. Another difference is that residential systems are not required in every room thus bathrooms, closets, and pantries are often not included. The driving principle of these systems is for life safety rather than property protection thus its design goals include preventing flashover in the room of origin and increasing the possibility of escape (Geisler, 2010, p.196). The latter design goal is very useful in buildings whose occupants cannot quickly escape or evacuated due to physical incapacity such as hospitals, and others. Fire sprinklers allows increase in travel distance limit to an exit, provides for reduced fire resistance in walls and doors resulting not only in increased chances of survival but savings in construction cost (Smith & Harmathy, 1979, p.191). 1.3 Sprinkler Type and Performance Sprinkler performance can be improved several ways. One is by installing sensitive sprinkler heads that will quickly respond when it reaches operating temperature. For instance, the ESFR or Early Suppression Fast Response Sprinkler can deliver high volume of water in the early development of fire because of its fast-response operating element. A Large-Drop Sprinkler on the other hand can generate high percentage of large droplets because it has 15.9mm orifice and a nominal K factor of 11 that is very useful in penetrating high velocity fire plume. (Solomon, 2002, p.401) Wet-Pipe Systems are widely used in buildings where there is no risk of freezing. A water supply provides pressure to the piping while automatic sprinklers hold water back until it is activated. When temperature from fire trigger the heat-sensitive element of the sprinkler, water is released to control the fire. This type of sprinkler systems is the simplest, more reliable, effective and cheaper. However, like any other sprinkler system, water from wet pipes can cause irreparable damage to building contents (Lord & Lord, 1999, p.187). Moreover, since water pressure is constantly present in a wet pipe configuration, fatigue can cause leak to links and discharge water accidentally. In cold weather for instance, frozen pipes can weaken the joints and burst causing tremendous damage to property (Wallace et al, 2010, p.375). In contrast, the Dry-Pipe valves initially in a closed position located in a heated space. It prevents water from entering the pipe until sufficient temperature from fire activates the sprinklers. Since the air pressure must drop before water can enter the pipes and released through the sprinklers, delays may be experienced and allow fire growth until sprinkler is activated. This is the reason why the Wet-Pipe Systems is widely favoured over Dry systems but in cold climates, dry pipes are superior over wet pipe (Kubba, 2009, p.357). Aside from the usual leak inherent to failing sprinkler system, dry pipe systems are more complex to install and maintain. Its size is limited and do not allow add on to existing system (Wallace et al, 2010, p.375). A Pre-Action System uses a dry pipe approach but the valve controlling the water is activated by a separate fire detection system. The process involved in this system is simple. When the fire detection system detects the fire, the pre-action system releases the valve and allows water to enter the pipe and hold it until the head’s thermal link fatigues and allow water to flow into the fire. Pre-action systems are also called double-interlock system designed for mission critical areas. Since the pipes are dry and filled with compressed air, chances of water leak are low. Moreover, leaks in the system are easily identified by low-pressure switches and increased operation of the air compressor (Curtis 2011, p.375). The disadvantages of pre-action system are it high cost and short delay in releasing water (Wallace et al, p.376). The Deluge Systems are commonly used in environments that require special sprinkler protection and activated separately by fire-detection systems. Sprinkler heads of these systems are open while the pipe is not pressurized with air. Moreover, heat-sensing operating element of this system is removed during installation in order to allow smoke or heat detectors, installed in the same area, to control the system. Unlike other system, there is no water in system’s pipe until the system operates. The deluge valve installed in the water supply connect prevent water from entering the pipe. Since the heat-sensing element in this automatic sprinkler is removed, failure of smoke and heat detectors can affect its functions and reliability. Therefore, it is imperative that these detectors are maintained properly (Kubba, 2009, p.361). Aside from being costly, Deluge Systems are only suitable to areas water damage is minor concern as it deluge sprinkler will soak the area with water. A Cyclic Sprinkler System is more of a head type than a system because a built-in thermostat controls its head. This thermostat is installed in the head itself and opens when it reaches a certain temperature. Unless damaged, Cyclic Sprinkler heads need no replacement after a fire. However, one drawback of this sprinkler is that it only discharged enough water to keep the fire in the smouldering stage resulting to a lot of smoke (Fischer et al, 2008, p.272). 2.4 Design, Installation and Maintenance of Sprinkler Systems – BS EN 12845 Design, installation, and maintenance of fixed fire fighting or automatic sprinkler systems according to BS EN 12845 must be of high standard. Design and installation of these sprinkler systems are determined by hazard classification. For instance, areas with low fire loads with low combustibility and compartments with fire resistance of at least 30 minutes are considered Light Hazard or LH. The maximum protected area for LH is 10,000 square meter/control valve (UK Copper Board, 2005, p.1). Ordinary Hazards or OH is those with medium fire loads and combustibility. The maximum protected are for OH is 12,000 square meter/control valve. OH1 is for cement works, sheet metal product factories, hospitals, and so on while OH2 is for car workshops, bakeries, breweries, museum, and so on. OH3 and OH4 are for buildings with high combustible load such as storage facilities with highly combustible chemicals (UK Copper Board, 2005, p.1). BS EN 12845 requires sprinkler systems installed in LH to remain in operation for at least 30 minutes while 60 minutes for OH. This entails enough volume of water with specific discharge rate to sustain the operational period requirements as shown below. Figure 1 - Hazard and Corresponding Design Density (Source: UK Copper Board, 2005) Water density for Light hazard system or LH should allow at least 2.25 mm/min discharge while OH1 to OH4 systems should have at least 5 mm/min. Pipe sizing for sprinklers should be from hydraulic calculation including pipe friction loses. Pipe friction loss is calculated using Hazen-Williams formula as shown below. Where: p is the pressure loss L is the equivalent length of pipes and fittings in metres Q is the flow through the pipe in L/min d is the internal diameter of the pipe measure in mm C is a constant for the pipe material where cast iron = 100, mild steel = 120, and stainless steel = 140, and copper = 140. Note that water velocity should not exceed 6m/s through valves and 10m/s in any other point in the system. BS EN 12845 also requires pipe works to have adequate corrosion resistance and for this reason, pipes should be either steel or copper and easily accessible. Pipes should not be buried in concrete floors and not to disturb the flow of water. For instance, steel work should be screw threaded or welded to avoid interference. Similarly, copper pipers should be joined with fittings specified by EN 1254. Joints between copper and steel should be flanged using stainless steel bolts. The spacing or location of sprinklers should be within supplier recommendation regarding the area coverage of single head. The minimum distance between heads is 2 metres (UK Copper Board, 2005, p.4). Design and installation for Life safety using BS EN 12845 entails additional requirements. Sprinkler systems designed for Life safety reasons can only use hazard classifications OH1, OH2, or OH3 regardless if such fire hazard qualifies for LH only (FIRAS Explanatory Guidance Note, 2009, p.5). 1.4 OH3 Sprinkler System Design for Single Storey Building INSERT YOUR DESIGN AND CALCULATION HERE 2. Summary Sprinkler systems generally detect a fire in its early stages. The goal in their development is protect life and property by providing 24/7/ 365 protections from fire. Sprinkler systems reduce construction cost due to compartmentation, material fire ratings, and so on. It enhances life safety by reducing probability of death or injury. It prevents fire spread, smoke, toxic gases, and poor visibility. Some sprinklers have fast response capabilities such ESFR while others are installed with independent heat and detection systems such as Deluge and Pre-action Systems. Although Wet-pipe systems are widely favoured, dry types may be better in terms of leaks and fatigue such as double-interlock systems providing two steps leak protection. Design and installation of sprinklers should comply with BS EN 12845 hazard classification including water volume, rate of discharge, pipe work, and operational period. 3. References American Waterworks Association, (2008), Distribution System Requirements for Fire Protection, AWWA, US Cote A, (2003), Operation of Fire Protection Systems, Jones & Bartlett Learning, UK Curtis P, (2011), Maintaining Mission Critical Systems in a 24/7 Environment, John Wiley & Sons, US DOH, (2007), Firecode – Fire Safety in the NHS: Guidance in support of functional provisions for healthcare premises, The Stationery Office, UK FIRAS Explanatory Guidelines Note, (2009), Residential & Domestic Sprinkler Systems, FIRAS, US Fischer R, Halibozek E, & Green G, (2008), Introduction to Security, Butterworth-Heinemann, US Geisler M, (2010), Fire and Life Safety Educator, Cengage Learning, US House of Commons,(2009), Orders 2009 Relating to Domestic Fire Safety, The Stationery Office, UK Kubba S, (2009), LEED Practices, Certification, and Accreditation Handbook, Butterworth-Heinemann, UK Lord G. & Lord B, (1999), The Manual of Museum Planning, Rowman & Littlefield, US Smith E. & Harmathy T, (1979), Design of Buildings for Fire Safety, ASTM International, US Snow D, (2003), Plant Engineer’s Reference Book, Butterworth-Heinemann, UK Solomon R, (2002), Fire and Life Safety Inspection Manual, Jones & Bartlett Learning, UK UK Copper Board, (2008), Commercial Sprinkler Information: Content of EN 12845, UK Copper Board, UK US Fire Administration, (1989), Residential Fire Sprinklers Retrofit Demonstration Project, FEMA, US Wallace M, Webber L, & Webber L, (2010), The Disaster Recovery Handbook: A Step-by-Step Plan to Ensure Business Continuity and Protect Vital Operations, Facilities, and Assets, AMACOM, US Read More