Fire Protection Engineering: Pressurisation Systems and Sprinkler System Design - Term Paper Example

Name of Student Student’s number Institution Course Code Instructor’s name Date Fire Protection Engineering Introduction Fire tragedies have been in occurrence in recent times where they have resulted in huge losses arising from damage of property or even loss of life. If most of these fires had been detected and stopped at their earlier stages, then the damage could have been reduced drastically, or even the fire put off completely. There lies a variety of strategies that can be applied in order to control fires in the early stages hence limiting the spread of damage to a small area while reducing disruptions to in operations and, most importantly, reducing loss of life. Among these methods is the use of sprinkler and pressurization systems. These are very vital safety features that should be installed in any building (NFPA, 2003). However, in order to guarantee optimal performance, sprinkler and pressurization systems ought to be properly installed and maintained regularly (Jones, 2008). A defective system or one that is not properly installed and serviced may have a lot of negative impacts such as wasting water due to leaking or even failing to work when a fire occurs. Therefore, it is very essential to ensure proper installation and maintenance of these systems. Proper functionality can be achieved by regular servicing, maintenance and testing which helps identify any damaged or defective system (NFPA, 2003). This report addresses pressurization and sprinkler systems and how they should be installed in a building in order to reduce loss of life and property damage in the event of a fire outbreak. Overview of pressurization systems Pressurization systems are provided with the aim of maintaining safe conditions, through smoke control, within an area that could be used as a means of escape and fire fighter access in the event of a fire. Pressurization is a technique aimed at ensuring that escape routes are protected against the ingress of deadly smoke. This is achieved by maintaining the pressure within the escape routes and fire isolated exits at a pressure higher than that of the adjacent spaces (Colt, 2012). In high rise buildings, these escape routes and exits are mostly vertical exits such as stairs and thus the term stair pressurization. The prime effect of pressurization systems is creation of an air velocity via the openings from the escape routes so as to minimize the spreading of smoke against the direction of flow into the exits. To achieve this, a minimum air velocity of 1m/s should be maintained. These systems are often required as part of a buildings fire strategy to protect a fire fighting shaft or to compensate for any non-compliances in other aspects of design. There are various design codes for the design of pressurization systems. It is very essential that the design of the systems be carried out by persons with the relevant experience in order to guarantee optimal performance of this system. A pressurization system is made up of two main components; supply air and Air release. Supply air is the air that is instilled into the area to be protected while air release is the air and smoke that is released from the adjacent fire area. The two elements are combined together creating a positive pressure difference (COLT, 2012). Venting Accommodation areas It is necessary to vent accommodation areas as this reduces pressure build up on the accommodation sides. A low resistance path should be provided to ensure air supply leave the unpressurized side of the space (COLT, 2012). Examples of vents are: Windows (should be distributed evenly around the building) Vertical dumping (Damper to automatically open on the fire floor) Mechanical extraction using high temperature fans and compartmented shafts. A typical pressurization system that is designed, manufactured, installed and commissioned to meet the required standards consists of the following: (a) Inlet Fans These are required in order to provide sufficient air into the designated area. Both the run and stand by fans and control equipment should be installed in a separate plant room and also protected from smoke. For high level inlets, dual inlets with automatic smoke dampers should be used. (b) Outlet Grilles and ductwork They are required in order to provide even distribution of air to the exact areas where it is required. The maximum distance between the supply grilles should not exceed 3 storeys. (c) Pressure relief Damper They are essential for releasing excess air in the closed air condition from the stair area. The purpose of ducting is to ensure that it discharges directly to the atmosphere independent of the wind direction. Damper blades ought to be set to begin opening at a differential pressure of 50 Pa. (d) Air release Automatic air release ventilations are used to prevent the build up of unwanted pressure in the adjacent spaces. (e) Pressurization systems control panel Pressurization systems should be installed to operate automatically from the smoke detection system (Cote, 1997). A manual On/off switch should also be provided either within: The pressurization plant room Near the entrance of the building (in order to suit the fire service) Within the central building services room. Requirements for pressurization systems There are 2 requirements that ought to be maintained within a pressurization system. These requirements are: (a) Maintaining a difference in pressure for a closed door condition. (b) Maintaining a velocity for an open door condition. Pressurization systems should be designed carefully in order to acquire the correct balance and also make the system work effectively. An insufficient pressure difference across any closed door will permit the passage of smoke into the protected area. On the other hand, excess pressure will hamper door opening hence escape (Cote, 1997). (a) Closed door condition Pressure difference is required in order to overcome buoyancy pressure that is generated by the hot smoke layer, the expansion of gases in the compartment as a result of heating, stack and wind pressure. (b) Open door condition For an opened door condition, maintaining a velocity is required in order to hold back smoke on the fire floor once the door onto the fire floor is open. Elements of a pressurization system As discussed earlier, a pressurization System has two major components; Supply air and exhaust air system (COLT, 2012). The two components are as shown below. A. Supply air system This system is fan powered and blows a sufficient quantity of air into the protected spaces in order to maintain the required air velocity or pressure level. It has 3 major modes of operation: Mode 1: The Detection Phase It raises a pressure differential in the area to be protected by the required amount when all doors are closed. Mode 2: The Escape Phase Its function is to maintain a specific air velocity through the open doors onto the fire floor with the other doors open. Mode 3: The Fire Fighting Phase It maintains a specified air velocity through the open doors onto the floor of the fire with the various doors open. B. The Exhaust Air System This system ought to be designed in such a way that it provides a low resistance route for the supply air to leave the building through the floor of the fire. In order to achieve this, a variety of methods can be used. These are: (a) Through the leakage provided by the window cracks on the outside parts of the building (Cote, 2003). (b) Automatically via the vents or open windows around the perimeter of the building. However, this is only possible where the concerned area has enough wall space to accommodate the necessary vent area. (c) Providing a vertical duct through the building while arranging a damper to automatically open on the fire floor. This is the most effectual method as it ensures a low resistance path. (d) Mechanical extract coming from the unpressurised space. There are various methods of achieving this. These are: (i) Providing the vertical duct with an exhaust fan that is chosen to overcome the resistance of the duct work as well as handle the hot smoke. (ii) Utilizing any mechanical exhaust system that exists from the unpressurised space. Advantages of using powered exhaust systems There are two main advantages of using a powered exhaust system from the fire room. 1. An exhaust fan would be chosen to overcome any form of resistance from the exhaust vent. The pressure residue from the stair case, with the doors open, would be reduced as well as the quantity of air leaving the building via the exit door. This would result in a reduced quantity of supply air into the system. 2. The system can be designed in such a way that it removes more air than that supplied by the pressurization system. This would create a negative pressure in the fire area as compared to the rest of the building. This ensures that all the air flow through the building is directed towards the fire area. Therefore, smoke will be prevented from entering parts of the building that are unaffected (Jones, 2008). Designing an effective Pressurization system There are a number of pitfalls that should be avoided in order to ensure that a smoke ventilation system provides fire safety in all necessary situations. The following practices are aimed at helping the designer avoid these pitfalls and as a result design a pressurization system that is effective. 1. Build quality It should be ensured that the builders achieve the desired level of build quality. This is by for example ensuring that penetrations are sealed properly, there are no gaps between the mortar joints and that the plasterboards are continuously sealed. 2. Air inlet ventilator sitting The correct sitting of the air inlet ventilators is very vital as it prevents the pressurization system from filling the stairs with smoke once smoke contaminates the pressurization air inlet. 3. Quick response to change in conditions In order to ensure correct design conditions, pressure controlled inverters, with the ability to respond rapidly to changes in conditions, may be used. A quick response to changes in conditions is essential for any pressurization system to function properly. Otherwise, the internal space can be over pressurized by the fans, slamming the doors and making them difficult to open. 4. Adjustable door closers Adjustable door closers should be correctly set up during commissioning in such a way that inward opening doors do not require excessive force to open as well as preventing outward opening doors from being blown ajar. 5. Correct commissioning Correct commissioning is very critical and should be carried out by qualified individuals. Therefore, ample time should be allowed for it. The final commissioning cannot be fully complete until all finishes are in place and until the building is ready for occupation. This is because small changes in the finishes can greatly affect the performance ability of the pressurization system (COLT, 2012). Service and Maintenance of smoke pressurization systems After the smoke pressurization systems have been successfully designed and installed by qualified personnel, it is vital that the systems get serviced and maintained regularly in order to ensure that they function optimally. Proper service and maintenance involves carrying out weekly tests to ensure that: (a) The electrical supply wiring is well protected. It should be ensured that the main supply is in such a way that the pressurization fans continue to run even when electrical supply is switched off. (b) The smoke detection, fan switching mechanism, emergency power supply and the venting equipment are functioning properly. (c) Annual pressure measurements and flow rates maintain efficiency levels. Sprinkler Systems Design and Installation Sprinkler fitting and installation involves installing, inspecting, testing, and certification of sprinkler systems in different types of structures. They are designed for the purpose of suppressing or controlling fire and should therefore be designed, installed and maintained properly to ensure effective performance (Brannigan, 2007). After installation of sprinkler systems, a commissioning certificate should be issued in order to provide the highest possible assurances and offer a high level of quality, safety and reliability. Classification of sprinkler systems is done according to the building’s level of hazard- light, ordinary or extra hazard. After the hazard classification has been determined, the design area and density are determined by referencing tables in the National Fire Protection Association standards (NFPA, 2003). After the design area is determined, calculations are carried out to verify that the design can efficiently deliver the required volume of water over the required area. The calculations also account for all the pressure lost or gained between the source of water supply and the sprinklers expected to operate in the design area (Cote, 2003). During installation, it should be ensured that the sprinklers are located in an open space area without any obstacles in the spray pattern. According to the rack storage fire tests, sprinklers work most efficiently with clearances of 18-inches. Therefore, there should be an 18 inch clearance between the top of storage and the ceiling sprinkler deflectors. Installations of sprinklers should be done below a flat and horizontal ceiling construction using approved one-step cement. Listed hangers can also be used for sprinkler piping mounted onto the ceiling wall directly (Puchovsky, 1999). In Light Hazard pendent sprinklers, maximum quick response temperature is rated at 77 degrees Celsius. The deflectors should be within 203 mm (8 inches) from the ceiling with the maximum distance between the sprinklers not exceeding 15 feet (4.57 mm). The piping will be mounted directly onto the ceiling. For light hazard horizontal side wall sprinklers, the quick response temperature is listed as 93 degrees Celsius maximum. The deflectors should be installed 12 inches (304 mm) away from the ceiling and 6 inches (4.27 mm) away from the side wall. The piping shall be installed directly onto the sidewall (Bromann, 2001). Light Hazard Upright Sprinklers should have the deflectors installed 4 inches from the ceiling with a maximum distance of 15 feet between the sprinklers. The maximum distance between the ceiling and the centre line of the main pipe should not exceed 8 inches. The distance between the closest hanger and the centerline of the sprinkler should be 3 inches (Puchovsky, 1999). Design for the OH3 fire sprinkler system The OH3 (ordinary hazard group 3) sprinkler system should be designed and installed with a water source with sufficient capacity to provide the required flow rate while at the same time ensuring that the sprinklers remain in operation for a minimum of 60 minutes (Cote, 1997). The design for an OH3 system should have a 5mm/min discharge over a total area of 216 square meters as required by the European standard (Puchovsky, 1999). The project design will be as shown below. Calculations Compartment 1 Total area = (18 * 17) meters = 306 m2 Area covered by each sprinkler = 216 m2 Number of required sprinklers Calculated by dividing the total area by the area covered by one sprinkler = 306 / 216 = approx. 2 Volume of water required = (0.005m/min * 60 min) * (2 * 216 m2) = 129.6 m3 Distance between sprinklers and side wall = 6 Inches Compartment 2 Total area = (16 * 25) meters = 400 m2 Area covered by each sprinkler = 216 m2 Number of required sprinklers = 400/216 = approx. 2 Volume of water required = (5 * 60) * (2 * 216) = 129.6 m3 Total volume of water required = 129.6 + 129.6 = 259.2 m3 Conclusion Fires can result in extensive damages to property or even loss of life once they occur. All necessary measures should therefore be put in place to reduce the chances of their occurrence as well as put them off when they occur. This can be achieved by use of sprinkler systems and pressurization systems among others. However, a malfunctioning or defective may have very many undesirable effects on a structure when a fire breaks out (Jones, 2008). This may be in the form of destruction of property, loss of life and interruptions in operations. Pressurization and Sprinkler system malfunctioning can be avoided through proper design, installation, service, and maintenance. It is therefore vital to engage qualified personnel to handle the design and installation work in order to have a dependable system (Jones, 2008). References Brannigan, F. (2007). Brannigans Building and Construction for the Fire Service, Jones & Barlette Learning, Sudbury, Massachusetts. Bromann, M. (2001). The design and layout of fire sprinkler systems, CRC press, Florida. Pressurization System from Colt Int’l - Smoke and Fire Ventilation. [ONLINE] Available at: http://www.coltinfo.co.uk/products/pressurisation-system-smoke-fire-ventilation/. [Accessed 03 August 2012]. Cote, A. (1999). Fire protection Handbook, National Fire Protection Association, Massachusetts. Cote, A. (2003). Operation of Fire Protection Systems, Jones & Barlette Learning, Sudbury, Massachusetts. Jones, A. (2008). Fire Protection Systems, Cengage Learning, Stamford. National Fire Protection Association, (2003) Standard for the Installation of Sprinkler Systems, Viewed on 03 August, 2012. Puchovsky, M. (1999). Automatic Sprinkler Systems Handbook, National Fire Protection Association, Massachusetts. Read More