Natural and Mechanical Smoke Ventilation Systems in Apartment Blocks - Report Example

Name Tutor Course Date Review of Natural and Mechanical Smoke Ventilation Systems in Common Corridors of Apartment Blocks Introduction Smoke ventilation systems are a very important design requirement in modern domestic and commercial buildings. These systems go a long way to contribute to the safety of occupants especially in case of a fire. The systems are designed to provide an exit for smoke and heat in the event of a fire and they go along way to ensure that the heat and smoke do not accumulate beyond a given level. Awbi argues that since heat is not allowed to accumulate in the building, casualties are therefore minimized. Yet again, most fatalities in the event of a fire result from inhalation of smoke and not from the fire itself. Smoke ventilations therefore play a major role in reducing such casualties. These ventilations also ensure that fire exits remain clear while fire services are also able to access fire points free of smoke. Natural Smoke Ventilation Systems Natural ventilations are very effective for smoke control if properly designed. In the event of a fire, the high level outlet vents and the low level inlet vents automatically opens to allow cool fresh air in while conveying the hot air and smoke out. Sicherheitssysteme points out that without these ventilations; smoke fills the room concentrated towards the floor by the convection currents of the rising hot air. The presence of such dense smoke greatly reduces chances of occupants to successfully escape. The design of such systems therefore requires specialized expertise with extensive knowledge of the associated international standards The natural ventilation has an added advantage since the openings could also be used on normal days to achieve a comfortable indoor environment depending on the weather. The system monitors temperature and automatically opens or closes these openings to allow in just the desired amount of air (smoke ventilation). It is a regulatory requirement that in large buildings, the corridor and lobby must be provided with a vent. The vent however must be located as high as possible so that the top edge is not below the top of the door to the stairs. In single stair apartments, the smoke vents should be provided with smoke detectors that function as the actuator of the vents. The system will therefore work automatically to open the vents at any instance smoke is detected. The detectors should however be positioned in the common access areas of the flat. In the cases where more than one staircase is available, actuation of the vent may be done manually. In this case however, the system must be designed so that the vent on the fire floor does not open before the one at the head of the stair. It is required that the vents be positioned on the external wall and must have a free area not less than 1.5m2. In the event that the corridor is not directly adjacent to the external wall a shaft must then be used, the operation of which can be natural or mechanical. The smoke shaft must however be erected vertically (Sicherheitssysteme p.44). Legislative requirements in design of natural smoke ventilation systems In the UK, legislative requirements derive from the building regulations for England and Wales (2000), with detailed requirements for apartments provided in Approved document B (ADB) 2006 where it is required that the smoke ventilation systems are designed to provide means of escape (MOE) for those within the building. Buildings 18m and above have been designed to include a fire-fighting lift to comply with the regulations. This requirement is also observed in buildings with basements 10m deep or more (smoke control in apartments and Fire Fighting Shafts). The standard BS 9999: Access and facilities for fire fighting requires that fire fighting cores without a lift be provided for more than two basements with areas more than 900m2 each. Fire fighting cores are meant to give fire fighters easy time while the attack the source of the fire. They are smoke free routes to the higher floors that allow fire fighters continue their work from positions of guaranteed safety. They include a protected lobby and/ or staircase and a fire fighting lift (Stationery Office, Great Britain pp.6) In buildings where the stair, corridor or lobby extend to the external wall, there may be used Openable Ventilators (OV) or Automatically Opening Ventilators (AOV) to channel the smoke to the outside. For closed corridors where direct access to the outside environment is not possible, smoke shafts with dampers or fire doors have been used. For natural smoke ventilation, the shaft must be of 3m2 minimum cross section according to the standard BS 5588 part 5:2004. At the top, the shaft is covered by an Automatically Opening Ventilator while at the bottom, there may be provided an Automatic opening Ventilator or a fire damper which must again be provided 1.5m2 minimum free area. To further protect exit/escape routes, pressurization systems have been used to maintain a high pressure in these areas. This helps to keep smoke from adjacent spaces away from such escape areas. As required by the Approved document B (2006) (ADB), any corridors that open into the staircase must be provided with ventilation since it is agreed that in the event of a fire in the apartment, smoke is likely to spread though the corridor into the stairs. All efforts must thus be made to prevent entry of this smoke into the staircase while occupants escape. It is within requirement for smaller buildings no more than 11m high that only staircase ventilation be provided so long as the escape distance in not more than 4.5m in the corridor. For larger buildings escape distance need not be more than 7.5m in one direction or not more than 30m if escape is in two directions. Any corridor and lobby opening to the staircase must however be ventilated. Landlocked corridors as in figure B and C are provided with a shaft as shown while in figure A an AOV is suitable ventilation. Mechanical smoke ventilation systems and associated legislative requirements Mechanical smoke ventilation systems have also been designed and have performed just as effectively as the natural smoke ventilation systems. Mechanical systems exhibit specific advantages as compared to natural system since these systems operate according to system specification and set values. Such mechanical systems are designed to work automatically. They are normally actuated by smoke detectors mounted on the common access areas of the apartments. The design of these systems must however follow the recommendations as outlined in the ADB (Smoke Control Association p.25). When designing these systems, there must be provisions for air inlet. This is important since smoke extraction is done by a powered machine which may cause pressurization or depressurization of the building and, among other things, cause damage to the system. According to Smoke Control Association, the extraction must therefore be carried out at convenient rates (25). Apart from resulting to depressurization or pressurization as has already been mentioned, high extraction rates may cause the exits or escape doors close tight or remain open due to the associated pressure differentials. It required that during such designs, the engineer must ensure that response to detected smoke must be confined to the floor of origin only. In this way, only those vents in the floor of fire origin are opened while those of the other floors kept closed especially when multiple floors are connected by the same vent. This ensures that smoke will not unnecessarily spread to unaffected floors. Again, it will avoid reduction of rate of extraction from the floor of origin. The smoke shaft must be of a non combustible material while all the vents m must be equivalent to an E30S fire door. As outlined in Approved Document B, most mechanical smoke ventilation systems are developed to function as natural smoke ventilation equivalents. However mechanical systems may be designed to provide higher performance and thus give longer travel distances. Care must however be taken in such cases since these doors goes a long way to limit the area that will need evacuation while at the same time they help protect fire fighters while they seek the source of the fire. The system must therefore adhere to guidance as provided in section 5. While locating the mechanical smoke ventilation equipment design requirements indicate that consideration must be given to the position of the staircase in the building and care must be taken to ensure that smoke must never spread to the stair at any time. While considering the staircase however, the designer must not forget the safety of the escaping people as well as that of the fire fighters. It is therefore common practice to position the extraction and inlet points so that extraction is done in a direction away from the stair (Smoke Control Association 24). Depending on the design requirements of the apartment, a designer may choose to have Mechanical extract-mechanical inlet system or Mechanical extract-natural inlet ventilation systems. In both cases, the mechanical system may be operated on variable extraction rate or steady extraction rate. In the variable extraction rate systems, the rates may be varied depending on the stage of the fire and may be increased immediately escape is over and fire fighting activities commences. Indicative layouts showing typical mechanical extraction-natural inlet ventilation and mechanical extraction mechanical inlet solutions for a common access corridor using a smoke shaft are shown below: Natural inlet mechanical extract layout (Smoke Control Association 27) Mechanical inlet mechanical outlet layout (Smoke Control Association 28) Comparison of mechanical and natural smoke ventilation systems Mechanical systems therefore brings with it advantages of high efficiency and reliability while still requiring a reduced shaft cross section area. At the same time, putting these systems in place will mean extra costs since they will require among other things, a dedicated power supply, extra wiring that should be fire resistant, and fan units. The dangers of pressurization or depressurization are also associated with these systems. On the other hand, although natural smoke ventilation may not be very reliable, its initial costs are far much reduced and on proper design according to legislative requirement, they give satisfactory performance. The choice of which system to be adopted will therefore largely depend on the specific requirements of the building and the amount of money available. Small apartments could comfortably be designed with natural smoke ventilation systems while large apartment with deep basements will require a mechanical smoke ventilation system. Works Cited Stationery Office, Great Britain. The Building Regulations 2000: approved document, B: Fire safety, Vol. 2: Buildings other than dwellinghouses: B1 Means of warning and escape; B2 Internal fire spread (linings); B3 Internal fire spread (structure); B4 External fire spread; B5 Access and facilities for the fire service, Volume 2. London: The Stationery Office, 2007. Sicherheitssysteme, Fachverband. Maintenance of smoke and heat ventilation systems: Preventive fire protection ; legal aspects ; economic aspects ; maintenance and service. Frankfurt, M: ZVEI, Specialist Group for Electrically Driven Smoke Ventilation and Natural Ventilation, 2009. Awbi, H.B. Ventilation of Buildings, London: Routledge, 2013. Smoke Control Association. Guidance on Smoke Control to Common Escape Routes in Apartment Buildings (Flats and Maisonettes). Revision 1: June 2012. Federation of Environmental Trade Association.2012 . Smoke Ventilation Association. Guidance for the Design of Smoke Ventilation Systems for Single Storey Industrial Buildings, Including Those with Mezzanine Floors, and High Racked Storage Warehouses. Federation of Environmental Trade Associations, 1993. Read More