Pressurization and Ventilation, which is a Better Protection to High Rise Building Stairs - Literature review Example

Pressurization and ventilation, which is a better protection to high rise building stairs LITERATURE REVIEW According to Ferreira & Cutonilli (2008), the objective of existing design standards for protection of staircase in high rise buildings is to offer 'smoke-proof' enclosure that prevents movement of smoke into the stairwell during a fire incident. The current International Building Code (IBC) recognises three means of providing "smoke proof exposure": stair pressurisation system, mechanical ventilation of stairs and natural ventilated stair balconies (Wan-ki et al 2013; Hung and Chow 2001). The present review of literature explored the various aspects of pressurization system and ventilation systems and their application in high-rise buildings. Smoke control systems Comparing the low-rise buildings to the high-rise buildings, Lay (2012) discusses that the high rise buildings feature a number of intrinsic attributes, which increase the range, likelihood and seriousness of accidental fires such as longer periods of evacuation, higher load of occupant, issues of accessibility linked to response by the fire rescue as well as the distinct stack effects. Installing sufficient provisions for smoke control in the design process of high-rise buildings plays a crucial role in resolving these issues. According to Ferreira & Cutonilli (2008), "smoke control" denotes control of the flow smoke right through a building through active and passive means. Installing smoke and fire barriers with protective openings is, according to Lay (2012), a means of passive smoke-control. Wan-ki et al (2013) also argue that use of automatic sprinkler systems also offer a means of smoke control as they limit the extent and intensification rate of fires. To ensure this, Wan-ki et al (2013) comments that they cool the smoke as a result lessening the pressure and buoyancy differences. Pressurisation systems Staircase pressurisation systems, according to Ferreira and Cutonilli (2008), are popular methods of offering protection to exit staircase in tall buildings from smoke during an accidental fire. Ferreira and Cutonilli (2008) draw attention to the fact that staircase pressurisation system is reliant a single fan that has a ducted shaft directed to various injection points. The multiple fans are further spread above the stairs’ height. Putting this into perspective, Hung and Chow (2001) comment that the design recommendations for stair pressurisation systems consists of several standards and codes such as the IBC and the NFPA 92A, both of which specify the relevant degree of pressure differences. Several building codes such as NFPA 92 require that pressurisation be used rather than a smoke-proof vestibule to reserve the pressurisation system as the basic line of protection. Under such circumstances, malfunction of the pressurisation system places the evacuees and fire fighters at a high risk if incapacitation and even death. In a related review, Lay (2012) argues that pressurization system has remained a popular solution for protection of staircase enclosures in high-rise buildings. The principle through which the pressurised systems work is comparatively simple. According to Lay (2012), the pressurization system is designed to deter smoke from leaving out of the closed doors and into the stairs as it injects in clean air into the staircase enclosure. Under this circumstance, the pressure within the staircase is more intensive than the pressure from the nearby fire compartment. Afterwards, when the stair door is open, the system is designed to sustain movement of air through the open doorways, which resists the flow of smoke and prevents undue contamination of the staircase enclosure. Earlier evidence presented by Tamura (1989) was among the seminal works to raise red flags on the performance of pressurization systems, specifically in simulated environment, field trials ad test facilities. Budnick and Klote (1989) also studied smoke control using pressurised systems that emphasises the significant challenges linked to using the systems. According to Lay (2012), effective functioning of pressurization systems is usually held in doubt by some fire experts, fire-fighters as well as some distinguished engineers, who have raised red flags regarding the handy application of pressurization systems. Still, some past and current studies have established that pressurization systems are a standard aspect of tall building codes in the United States, United Kingdom, India, China and the United Arab Emirates as well as many other countries globally. Indeed, there is significant sketchy proof of the tribulations associated with pressurization systems. A survey provide by Lay (2012) indicates that fire fighters in the United Kingdom, United State and India have determinedly expressed concern that the lack trust for pressurization systems. Similarly, Lay's (2012) discussions with several fie engineers and safety officers in the three countries revealed their discomfiture with the pressurized systems. Ferreira and Cutonilli (2008) reiterate that the pressurisation systems are intended to safeguard the occupants of the building along with the fire fighters. Hung and Chow (2001), comments that evacuation of high-rise buildings is usually phased to disallow the occupants from moving to the escape stairs simultaneously. Rather, the occupants most at risk, or at the affected floor, are first allowed to evacuate ahead of the other occupants, from one phase to the other. The outcome of this is that the routes used for evacuation require protection from smoker for longer durations. In particular, pressurisation is intended to offer this protection. At this rate, Lay (2012) notes that Fire fighters will need to depend on pressurisation to ensure the environment is smoke free, where they can initiate their fire-fighting activities. While fighting the fire, pressurisation is intended to protection the escape route to allow the fire fighters to use it as necessary. The elevator and lobby cores may as well as be pressurised to contain movement of smoke. In circumstances where the elevators have to be relied on to support the evacuation and fighting, then pressurisation of elevators cores may be designed to ensure that the elevators are accessible as well as freed from contamination. While the pressurisation systems are considered to be popular in the United States, where they were initially used to ensure life safety of buildings are maintained, a study by Lay (1996) found that some 35 percent of the pressurisation systems are likely to fail. An earlier study by Tamura (1992) also found that none of the pressurisation systems he tested performed as intended. Problems associated with pressurisation systems As Lays (2012) describes it, the principles of a pressurisation system is simple yet the challenge linked to it are varied and complex. For this particular review, they are categorised into the challenges linked to commissioning, design, legacy, and operation. Regarding the challenges associated with design, Lay (2012) mentions that a range of basic design parameters have be taken into perspective. The most crucial parameters that affect the design are essentially estimates of leakages emanating from the core. The air leakage parts may consists of windows, stairway doors, doors of the elevator, crevices or gaps n the walls, or the service shafts. While standard estimates exist that are recommended for guiding the design of pressurisation systems, the calculations need to be precise to allow the system to perform effectively. However, this may not always be the case (COLT 2014). In addition, the designers or architects have to depend on the variables that are static from the "pint of design." In Ferreira and Cutonilli’s (2008) view, the remainder of the design process including the construction, refurbishment or subcontractor design also need to rely on these estimates throughout a building's lifetime. However, this is unrealistic as the estimates may always not be accessible, which makes the pressurisation systems to be unreliable in the long-term, particularly for buildings that survive for long periods. Hung and Chow (2001) acknowledge that while most engineers will traditionally include tolerances during the design process of a building, the tolerances cannot effectively guarantee adequate design flex that can contain substantial changes in leakage paths. At the same time, the desire to have an integrated building services design cannot be necessarily efficient as it is difficult to effect changes in the elements like sizes of fans, ducts, power supplies after the very first design process. The commissioning process also presents significant challenges to the effectiveness of the pressurisation systems. According to Lay (2012), it only happens on condition that the building is significantly completed. He adds that any major problem that is identified during the commissioning phase, which cannot be addressed by fine-tuning the equipment that has already been installed, has to be restructured. This may result to cost and time overruns of the building projects. Lay (2012) further comments that it is commonplace for the temporary doors to be already installed during the commissioning process. Sdditionally, buildings are usually designed and passed on as 'shells' and left for the tenant to perform the final fit-out. This may have substantial implications on the air supply and leakage paths. According to Wan-ki et al (2013), the outcome of the commissioning is highly conditional on the temperature and wind conditions during the day of testing. This discrepancy is addressed by the design codes intended for pressurisation systems, including the BS EN 12101- The BS EN 12101-6 consists of protocols for normalising the system that is tested against the conditions of climate during the day of testing. The consequence of this varies depending on the location and the height of the building. Still, in large cities with extreme variations in temperature across the year, as well as in cases of high rise buildings that experience wind effects as a typical feature, the importance of setting a system to allow it to function limited to a single climate potentially leads to performance problems of the pressurised system (Anon 2008). Hence, in while engaging in the design and construction process of a building, it may seem unfortunate that the consequences of weather on the endurance f the pressurised system is not taken into account. Indeed, while this may be the case, it is a matter of technicality. Next, the number of openings, such as doors and windows that are open at any single moment is crucial for establishing the rate of peak flow of the fans that serve the pressurization system. According to Ferreira & Cutonilli (2008), during the design process, it is normal for the doors situated at the foot of the staircase to be assumed to be opening during the actual process of fighting process to allow the fire fighters to make way into the building. Still, this may not depict the technicalities during the actual fire fighting or evacuation process in a high-rise building. In actual fact however, Lay (2012) opines that when any door is left open more than the small number supposed in the design process, it will lead to loss of air, which prevents the pressurisation system from functioning as required. As a consequence, it may potentially allow smoke to make way into the core. An additional principal concern for pressurisation systems actively in operation is its effects on the force at which the door opens. Ordinarily, doors open into the staircase. Due to this, intensified air pressure within the core that emanates from the pressurisation effect of the pressurisation system can deter the evacuees from easily opening the doors. Lay (2012) also comments that balancing the varied air flow requirements to create positive pressure can be tricky in a core that has closed doors as well as the extensive volume needed while the doors open. Such a problem tends to aggravate with the taller the building. In fact, the BS EN 12101-6 lacks reservations on the maximum height of any core's specific height. Ferreira and Cutonilli (2008) agree and further note that the effectiveness of pressurisation system are contingent on ensuring that the doors are largely closed to sustain the needed pressure differential in order to prevent smoke from flowing into the stairs. In their view, such a situation is impractical during the event of fire or in situations where the fire causes catastrophic damage to the staircase. Mechanical smoke ventilation systems Like the pressurised system, the basis for using mechanical smoke ventilation system in the stairs of high rise buildings is to prevent the movement of smoke into the stairwell to allow the occupants to escape from the building safely and for the fire fighters to access the building to the source of the fire. The Approved Document B (ADB) and British Standards provides guidance on smoke control systems basically through the natural means, such as through the use of natural smoke shafts and external automatic opening vents (AOV’s). According to Harkin (2013), an advantage of the mechanical ventilation system is that they offer cost-effective means of venting a fire-fighting shaft (Chow 2006). The ADB standards specify details where a fighting shaft needs to be installed into a high-rise building. The ADB recommends that a fire-fighting shaft needs to be installed in buildings that have floors beyond 18 metres the access level of fire a rescue vehicle. The ADB further specifies that in cases where firefighting shaft are installed to serve residential buildings, the smoke control provision for firefighting shafts may be similar to the vent of the common corridor. The reason for this is the high level of compartmentation that characterises residential apartment (Chow 2006). Studies have established that installation of mechanical ventilation system can substantially improve a high-rise building’s life safety (Harkin 2006: Chow 2006). According to Chow (2006), the significance of the mechanical ventilation system is to keep smoke away from the escape routes, eliminate smoke from the fire area in order to deter fire from migrating to other areas, to allow for fire-fighting operations and lastly, protect the life of the occupants and curtail loss of property. Harkin (2013) illustrates the fact that the mechanical smoke ventilation system works using the same principles as the depressurisation system. It eliminates heat and smoke from an affected area, hence depressurising the room. Since the surrounding area like the staircase will have greater pressure, it will facilitate air to be driven from these areas and into the smoke shaft as a result deterring movement of smoke into the stairwell and the adjacent areas. One fundamental weakness of the ventilation system, as Harkin (2013) explains, is that it requires installation of additional inlet air to the space to be depressurised in order to protect the area from excessive depressurisation. According to Hung and Chow (2001), in the event that mechanical ventilation systems are installed, a smoke detector should as well be installed. In case the space gets over-depressurised, damage to the smoke venting equipments are likely, which also means that smoke will be absorbed from the room affected with fire. The differences in pressure across the doors beneath the stairwell may also intensify, which can make the doors making them difficult to open. The components of air for the system are achievable in numerous ways. However, this would be contingent on the layout of design of the building. Harkin (2013) suggests fours ways this can be overcome: installation of natural inlet through external air, inclusion of natural inlet through AOV positioned at head of the stairwell, use of natural inlet through the shaft, and lastly mechanical inlet through a shaft. In further review, Harkin (2013) adds that the ventilation system ‘pulls’ away smoke and heat from the corridors. They are not dependent on the smoke’s natural buoyancy. In fact, Wan-ki et al (2013) explain that the shaft area may be considerably lessened in comparison to the natural system. On the other hand, the smoke shaft area for the ventilation system is contingent on several factors like the system’s extraction rate, the corridor size the fire loading in the room. The idea is supported by Ferreira & Cutonilli (2008), who add that it provides a challenge as they have to be calculated during the design process, based on the computation fluid dynamic (CFD) modelling. The calculation determines the system’s extraction rate and the area of the shaft. Studies have emphasised the effectiveness of mechanical ventilation systems. Harkin (2013) examined the natural smoke venting of a fire-fighting shaft using an exterior AOV in addition to an AOV opening to a natural smoke-shaft. He established that a 3 square metre shaft offered better outcomes in the fire-fighting shaft compared to an external AOV opening. Still, the mechanical ventilation systems can extract more smoke and heat from a room it is highly possible using a performance-based design approach to condense the ventilation shaft since that serves the fire-fighting shaft. In return, it offers cost-effective means to protecting the staircase from smoke movement. Still, Ferreira & Cutonilli (2008) express doubt that this may not be obviously so as it depends on such aspects as fire load inside the room as well as the rate of extraction by the fans as well as size of the opening of the AOV’s into the shaft. According to Harkin (2013), the mechanical ventilation has several advantages. First, it optimises the limited space at the stairwell. Next, it is also cost-efficient due to its potential to eliminate smoke from the stairwell and make effective use of the condensed ventilation shaft areas. Additionally, it is less complex compared to the pressurisation system. Harkin (2013) and Chow (2006) also agree on the disadvantages of the ventilation system. The two states that the ventilation system to be installed needs to be first approved to ensure it is standardised and can work through the CFD modelling and calculations. Summary Based on the survey of literature, it is clear that ventilation provides better protection to high-rise building stairs than pressurization. While the pressurisation systems are popularly used, they are more likely to fail. While the principles of a pressurisation system is simple, the challenge linked to it are varied and complex. The key challenges are categorised into three: commissioning, design, legacy and operation. The pressurization system is designed to deter smoke from leaving out of the closed doors and into the stairs as it injects in clean air into the staircase enclosure. Under this circumstance, the pressure within the staircase is more intensive than the pressure from the nearby fire compartment. Afterwards, when the stair door is open, the system is designed to sustain movement of air through the open doorways. Like the pressurised system, the basis for using mechanical smoke ventilation system in the stairs of high rise buildings is to prevent the movement of smoke into the stairwell to allow the occupants to escape from the building safely and for the fire fighters to access the building to the source of the fire. References Anon 2008, High-Rise Buildings, Jones and Bartlett Publishers, viewed 30 Mar 2015, Budnick, K & Klote, J 1989, “The Capabilities of smoke Control: Pat II - System Performance and Stairwell Pressurised," Protection Engineering vol 1 no 1, pp.1-10 Chow, W 2006, "Fire Safety Provisions For Supertall Buildings," International Journal on Architectural Science, vol 7 no 2, p.57-60 COLT 2014, Smoke control and day to day ventilation systems for multi-storey residential buildings, viewed 30 Mar 2015, Ferreira, M & Cutonilli, J 2008, "Protecting the Stair Enclosure in Tall Buildings Impacted by Stack Effect," CTBUH Technical Paper, pp.1-7 Harkin, R 2013, Mechanical Smoke Ventilation Systems (MSVS), Lawrence Webster Forrest Limited Hung, W & Chow, W 2001, "Review on Fire Regulations for New High-Rise Commercial Buildings in Hong Kong and a Brief Comparison with those in Overseas," International Journal on Engineering Performance-Based Fire Codes, vol 3 no 1, p.25-51 Lay, S 2012, "Pressurisation Systems Don't Work & Present a Risk to Life Safety," CTBUH Technical Paper Tamura, G 1989, “Stair Pressurisation Systems for Smoke Control: Design Considerations.” NRCC-30896 Wan-ki, C, Nai-Kong, F & Che-Heng, L 2013, "Fire Safety Strategies for Supertall Buildings in Hong Kong,” CTBUH Journal iss 1, pp.3-31 Read More