Fire Engineering Solutions: Smoke Ventilation Systems in Apartment Corridors - Report Example

Fire Engineering Solutions Prepared By Student ID Institution Date Table of Contents Review of Smoke Ventilation Systems in Apartment Corridors 4 Types of Smoke Control Systems 5 Natural Smoke Control system 5 Mechanically Powered Smoke Control System 8 General principles 8 Installation and Equipment 9 Testing and documentation 11 Conclusion 12 Part 2: Using CFD modeling 13 Conclusion and recommendations 16 Bibliography 17 List of Figures Figure 1: Ventilator opening …………………………………………………………..6 Fig 2: UniVent Stairwell System ………………………………………………………6 Fig 3: uniVent AOV and OV system…………………………………………………..7 Fig 4: Univent Louvre…………………………………………………………………..7 Fig 5: uniForce Pressurization……………………………………………………….10 Fig 6: UniForce Mechanical Smoke extract…………………………………………10 Fig 7: Scenario 1……………………………………………………………………….13 Fig 8: Scenario 2……………………………………………………………………….14 Fig 9: Scenario 3………………………………………………………………………15 Review of Smoke Ventilation Systems in Apartment Corridors Smoke and heat exhaust ventilation systems (SHEVS) are natural and mechanical systems that remove smoke from the building by allowing escape areas to be free of smoke to save life and reduce damage to the building. The three components of SHEVS include the exhaust ventilators for removing the smoke, smokes barriers for limiting the spread of smoke while it remains in the building and inlet ventilators for allowing in fresh air to replace smoky one that were removed via discharge exhaust. There is a high annual fire incidence in residential flats within U.K resulting over 300 fatalities mostly caused by effects of smoke. The need to protect common access routes is important to facilitate escape and operation of fire fighters. Builders are required to select a good smoke control system. A good fire control system should be able to prevent smoke from spreading through escape areas such as corridors, lobbies and staircases within the apartment to facilitate escape of residents and fire-fighting operations. This is realized by reducing obscuration, thermal exposure and toxicity in common routs for escape and enhancing rescue services and fore conditions. Designers of smoke control systems are required to follow guidelines by smoke control associations (SCA). The SCA guidelines sets out parameters and information that should be included into system design using CFD models and/or other computations. For the proposed systems to be approved, they must be able to complement the fire strategy of the building and offer correct and expected level of fire safety. This paper reviews both the natural and mechanical smoke control systems in common escape routes within the apartments. Types of Smoke Control Systems Most smoke control guidelines advocates for natural ventilation systems because they are highly reliable solution and economical. The use of mechanical systems is only recommended as alternatives where the use of natural ventilation in apartments is constrained. The selected system ventilation system for apartments must conform to the building regulations provided in Approved Document B (ADB). According to 2006 edition of ADB, lobbies, stairs and corridors opening up to stairs are common areas that need smoke ventilation (DiNenno 2008). Natural Smoke Control system Natural ventilation is preferred over mechanical ventilation because it is simple, economical and reliable with low energy use and noise. However, the effectiveness of natural ventilation is sensitive to effects of the wind and possibility of losing large floor space using natural shaft systems (Nesse 2005). The use of natural wall vents, vents at stair heads and natural vent shafts are recommended by ADB. The aim of natural ventilation is to harness the forces of wind and thermal buoyancy to facilitate the flow of air through the ventilator. Effective performance of natural ventilator requires a source of air inlet and exhaust opening. Mounting vent in the wall provides both air inlets through the bottom vent and exhaust at the top. It is also important to position stair door strategically to let in air when it is opened. Mounting a vent at the head of stairs is critical to vent smoke entering through stairs. When designing smoke, heat and exhaust ventilation (SHEV) solutions, it is important to consider and actuate shaft doors and free open area of windows to allow smokes to escape. It is also critical to deign doors, windows and ventilators that can be opened wide enough for a large opening to enable as much smoke to ventilate from the building. Despite lack of regulations, it is crucial to mitigate the negative effects of winds such as the possibility of blowing the smoke back into the corridor and the stairs. To realize this objective, designers ought to carefully select and locate vent to reduce susceptibility to adverse effect of winds. In a building roof opening will be used to vent in the light a minimum of 140 degrees angle is required as per BS EN12101 to reduce the negative effects of winds. For ventilations involving the side of the corridor and outward bottom opening vent, the free area is the product of distance the ventilator opens and the length of vent that is opposite to the pivot mechanism as shown in the figure below. Similar approach applies to smoke shaft doors where the height of the door and opening distance are captured in the calculations. It is however important to select shaft doors that open fully or to the maximum 90 degrees to provide the greatest area possible for the free area for effective ventilation of smoke via the shaft. ADB recommends that measures of free area for ventilator opening should be measured at right angles to the direction of airflow and in the plane where its area is at a minimum. Figure 1: Ventilator opening UniVent Stairwell System This is a stairwell ventilation system consisting of a control system and roof ventilator (County 2013). It is a ventilator for the stairwell with automatic opening hatch with 120 degrees opening angle meant to minimize the effects of the wind. It is manufactured from aluminum materials that resistant to corrosion and insulated with Rockwool. The system has a geometric free area of I meter square and is available in a variety of finishes. The kit for control consists of a local control, tow switches remotely controlled at the staircase bottom and top and 24VDC battery. Fig 2: UniVent Stairwell System uniVent AOV and OV system This is automatic actuator for converting windows to Automatic Opening Ventilators and Opening Ventilators. This is chain drive actuator installed to a broad range of windows and with appropriate kit consisting 300N, 380mm stroke and 24VDC battery, it can be used both OV and AOV. The kit further contains a local control panel and for the AOV, an optical smoke detector is included. The signal sends the signal that opens up a stairwell ventilator automatically. This allows the fitted window to open to a minimum of 60 degrees. Fig 3: uniVent AOV and OV system Univent Louvre This is the most versatile and attractive ventilator integrating with all types of building façade. It is fitted with double glazed louvres blades and a thermal broken aluminum frame to provide good insulation and leakage of air. This vent is used both as OV and AOV subject to control kit. Fig 4: Univent Louvre Mechanically Powered Smoke Control System General principles According to ADB recommendations, this is used as an alternative where the use of natural ventilation is constrained. In SCA guidelines, the use of mechanical system is based on shaft system and the level of the floor can have its own powered system. The benefits of mechanical systems include low sensitivity to forces of the wind, have specified extraction rates, reduced shaft across sections and overcomes system resistance (Sheard and Jones 2012). The requirement of mechanical systems include fire resistance wiring, the need for maintain power, standby fans and temperature equipment. It is important to consider internal pressures within the building and should also be limited to allow the doors to open. Air inlet into the communal area is necessary to prevent damage to the system and also to ensure there is no depressurization or excessive pressurization in the ventilated area. This is because, excessive pressurization interferes with the drawing of the smoke from the apartment and also avoids differentials in elevated pressure that could make it escape doors inoperable and cumbersome to open escape doors. Designers of the system are advised to avoid opening ventilators on multiple floors, particularly those connected with smoke shaft to prevent spreading of the smoke to areas of the building unaffected and reduce removal rate of the smoke from the floor of fire origin. It is also required to construct smoke shafts using non-combustible materials while all vents in corridors and lobbies should be resistance to smoke and fire to at least an E30S fire door. Typically, the system is activated upon detecting smoke in lobby or corridors and once activated, the smoke vents on floor with fire, those ahead of the stairway and vents at the top opens up and fans start running at designed speed. The provision of basic power systems are equivalent to the natural systems as provide for in ADB document. However, systems that can provide higher performance can possibly be designed to allow for extended traveling distances in the corridors. However due care must be observed while removing subdivisions of corridors. It is also essential to limit the prospective travel distance through smoke and removal of these doors has the potential of compromising the safety of fire fighters. Installation and Equipment The equipment of powered system must meet its specific requirement for effective performance. Installation has to be proper with all its components to ensure the system operates correctly and is able to meet its performance targets. A detailed engineering plan including the size, location and appropriate equipment with also power supply ratings, sizing and routing cables and cause and effect summary. It is important to the safety of users, environmental conditions, ease of access and protection should be considered when selection and installing components of the system. All system components should be safety maintained and cleaned after installation and accessible regularly for lubrication and cleaning to function smoothly. Beams and lifting eyes should be installed at the right place and doors and access panels be provided as per the requirements to facilitate the removal and repair of system equipment. System components should be installed such that they are able to prevent smoke and heat from discharging on to nearby and adjacent structure. Accordingly, discharge exhaust should point away from windows and walls and protect any combustible parts near the exhaust opening. uniForce Pressurization This system fully compliant and is engineered to save design, installation and commissioning time. The pressurization system provides a modular solution on the basis of the kevel of required protection and number of stories in the building. They are employed to protect escape routes by reducing entry of smoke in protected zones by raising level of pressure. High standard of protection and evacuation is guaranteed if it is correctly designed and installed. However, designing, implementing and commissioning is a laborious process and consumes time. Smoke pressurization Unit consists of inlet section for detecting smoke and shutting off dampers; fan section fitted with backdraft shutters; and discharge section fitted with integral control panel. Fig 5: uniForce Pressurization UniForce Mechanical Smoke extract This system removes smoke before it is accumulated thus protecting the escape routes such as stairs and corridors or lobbies. It is designed to offer simple modular solution with minimal risks possible. Fig 6: UniForce Mechanical Smoke extract Testing and documentation It is fundamental to test any system of smoke control ventilation to prove its performance against targets and design criteria. A smoke control system is basically a life safety system and assists fire and rescue operation, and hence imperative to be tested by installer and witness testing before it is approved by authority. Approval is subject to its conformity with approved design criteria and project specification. There are different types of documentation accompanying the handing of smoke control system over to end user. These include documentation with design information containing system’s performance criteria and system description. They include the cause and effect diagram or a control philosophy as well as drawings of installation and types of test certificates or appropriate CE marking documentation. Other documentation include commissioning, installation, witness testing certificates and any evidences to confirm the system was tested and approved by the authority, documents with instructions for fire service use and testing and maintenance instructions. The building regulations for England and Wales require the person conducting the work to provide adequate information to system in reasonable safety to operators and those maintaining the building. This is meant to assist the eventual occupier, employer or owner of the building in doing fire safety duties. Conclusion It is apparent from this review that any good smoke control system should be able to prevent smoke from spreading through escape areas such as corridors, lobbies and staircases within the apartment to facilitate escape of residents and fire-fighting operations. The use of natural system is preferable to mechanical system because of it is economical and reliable. The use of mechanical systems is only appropriate as alternatives where the use of natural ventilation in apartments is constrained. Part 2: Using CFD modeling This part examines the use of CVD modeling to control smoke in a 15 storey building provided in the plan. The building is to be constructed in Norwich city. The aspects to consider in CFD modeling include the escape time after detecting smoke, the characteristics of the fire, heat radiation and separating space, transportation of heat and smoke from the building and effectiveness of smoke control. In the provided plan, considering that fire begins on 4th of the 15-storey building with similar plan, the first action is to determine the heights of corridors and exit doors. In this case, the height of corridors in fourth floor is 3 meters high and all floors will have the same height because the plan is similar. In the CFD modeling, the exit doors will considered to be single leaf fire doors measuring 2 high by 0.8 in width with ambient temperature of 20 degrees Celsius. Therefore, fire will spread from the 9 meters square in the center of fourth floor corridor of the storey apartment. The CFD model to used has a heat flux of 702 kilowatts per square meters, implying that total size of thinning fire into different directions is 6,318KW. This case considers heat travelling rate of 0.231kj/s in 30 meters distance. Considering travel distance of 30 meters at a speed of walking one meter per second, it would take a the smoke 300 seconds. The surface thickness is 25 millimeters while the breadth of the corridor is 1.8 meters. Smoke detection time is 60 seconds while highest estimated temperature in fire plume will be 300 degrees Celsius. There would a single case stairs for all the floors. There would be vertical smoke shaft to ensure that common areas such as staircase are protected from the extreme heat and ensure visibility in the heavy smoke occupying the corridors. For all the scenarios shown, smoke visibility is limited to 8 meters while highest temperature will be capped at 65 degrees Celsius. The three scenarios provided shall be investigated and this will involve varying the location of fire sources and vertical smoke shaft to complete CFD modeling. This will ensure that the design will be able to account for any worst situation of fire in the building. The methods to be used to control smoke and heat in the storey-building provided in the plan is demonstrated by the three scenarios as shown below Scenario 1 This scenario shows fire source right in the middle of corridor on the left wing of the building on fifth floor. The distance from source of fire to staircases at the end of left wing is 20 meters. Due to effects of natural wind, it moves to the right direction towards the main exit and ti the fire detector at a speed of 1 meter per second. Smoke detector is located about 20 meters from the source of fire and this takes 20 seconds for fire alarm to ring. The response time for occupants on the left wing will be able to escape using the left staircases. It will also take about 20 seconds for the smoke to exit through the vent adjacent to smoke detector. In this case, the smoke is sensed late making it difficult for right wing occupants to escape early from the smoke. Fig 7: Scenario 1 Scenario 2 This case presets situation in which fire begins on the right wing on the 9th floor of the building and travels toward the left wing of the building. The fire is detected early, after 10 seconds as smoke detector is within 10 meters from the source of fire. In addition, smoke is able to exit via the shaft opposite the source of fire thus reduces the intensity of smoke. Occupants on left wing and upper floor of the building have adequate time to comfortably escape using staircases located at the end of left wing. Extinguishing the fire can also be done in time using mechanical system located close to source of the fire. Fig 8: Scenario 2 Scenario 3 This case shows fire starting next to the main exit route, the central staircase on the 13 floor of the building. However, smoke moves to the left of the building and smoke detector is just 6 meters away from the fire source and hence it is detected within six seconds and hence fire alarm rings to alert occupants. The smoke is able to exit via smoke shaft located at the extreme left end of the corridor. Occupants on 12th floor and below are able to escape downwards using staircases. However, those on 12th floor and above will have to use emergency exit to get out of the building. It is also easy to put out the fire using smoke vent over the fire source. Fig 9: Scenario 3 Conclusion and recommendations It is possible to use CFD modeling in the building in plan and three cases above have shown that it is possible to control smoke. This is possible by installing natural and mechanical shafts at bot ends of extended corridors and also near the escape routes. It is also important to maintain boundary and surface conditions in all parts of the building to facilitate evacuation of tenants through the central staircases. The owner is advised to install mechanical smoke shafts at extreme end of the corridor and staircases of the building. However, occupants should be made aware of safe evacuation when fire occurs. Bibliography Chen, Q., 2009. Ventilation performance prediction for buildings: A method overview and recent applications. Building and environment, 44(4), pp.848-858. County, C., 2013. Gleneagles Iii Apartments. Bid. DiNenno, P.J., 2008. SFPE handbook of fire protection engineering. SFPE. Dols, W.S., 2001. A tool for modeling airflow & contaminant transport. Ashrae Journal, 43(3), p.35. Li, J.S. and Chow, W.K., 2003. Numerical studies on performance evaluation of tunnel ventilation safety systems. Tunnelling and underground space technology, 18(5), pp.435-452. Nesse, R.M., 2005. Natural selection and the regulation of defenses: A signal detection analysis of the smoke detector principle. Evolution and Human Behavior, 26(1), pp.88-105. Sheard, A.G. and Jones, N.M., 2012. Powered smoke and heat exhaust ventilators: the impact of EN 12101-3 and ISO 21927-3. Tunnelling and Underground Space Technology, 28, pp.174-182. Read More