Fire Safety Engineering of a 20 Storey Building Block - Case Study Example

Fire Safety Engineering The following reports focuses on faire safety engineering, the construction and design of a 20 storey building block which has multi-occupied premises (50% - hotel and 50% - offices), in the city centre of Preston. The idea in the report is to investigate the construction material used along with the designs for fire safety taking into consideration practical, environmental and economic constrains on the building. The report also seeks to appraise the need to control smoke movement in this building and making a decision with regards to the extinguishing agents that should be used after examining the advantages and disadvantages and disadvantages of the same. Materials used in the building have to be a combination of a brick, metal, glass, concrete and plastic among other things. The basic material used in the building construction is concrete which is made up of cement and an aggregate composite such as sand. Metal is to be used in the structural framework of the building and the external surface covering. Steel is to be used for the structure. Other metals like aluminum, brass and zinc are to be used for specialty items. Glass has to be used in the windows and also in the designing of the building giving it a more look more pleasing to the aesthetic senses. Ceramics have to be used for tiles and fixtures such as counter tops. Besides these, plastics and foams such as polysyterene and polyuretane will also have to find place in the construction of the finish of the building. The building construction method can be that of steel framing which is not very common option for residential homes but very popular in commercial buildings. Benefits from adopting this method will include faster build, reduced dry out times and flexibility in project planning. Though not very common it can be a feasible option because of its low costs and easy maintenance. For a successful fire safety design we have to understand the interaction between a number of different components, such as: The fire source Smoke movement Heat transfer to the structure Detection Active fire safety features Human behavior and egress Toxicity The main objective of ensuring safety in building design is to reduce the level of damage to the building and its contents and to minimize the loss of life in the event of an accident or natural hazard. To achieve this objective the building has to have adequate resistance against accidental loads. In case of an accidental fire, the building should be able to withstand the fire for a reasonable time, and the fire should be contained within a localized part of the building. Several safety measures must be taken to meet the expected performance, including evacuating people from the building, detecting and suppressing the fire, stopping the fire from spreading, and protecting the load-bearing members from losing their strength at elevated temperatures. Site Requirements—the design seeks to integrate performance requirements associated with fire department access, suppression, separation distances and site/building security. Fire department access The layout has to be such that the fire department can zero in on the spot with as much ease as is possible. Provisions have to be made in order to provide rapid access to various features such as fire department connections, hose valves, elevators and stairs, key boxes, etc. Accommodate the access of fire apparatus into and around the building site Building Construction Requirements, at a minimum will have to address the following elements: The height of the various floors has to be in keeping with fire norms Occupancy types Interior finish The basics requirement that has to be kept in mind is that of exit from the building in case of a fire. For the purpose special care has to taken of the exit fire stairway. The factors to be kept in mind with regards to egress requirements are as follws Exit stairway remoteness Exit discharge Areas of refuge Accessible exits Door locking arrangement{security interface} The design of the building has to be inclusive of fire detection and notification systems. For the purpose fire detection devices have to be installed in all the key areas including corridors, staircases, elevators, rooms and toilets. The three main points to be kept under notice here are fire detection, notification and surveillance. Fire Suppression Requirements, at a minimum will have to address the elements such as water supply, type of automatic fire extinguishing system (Water-based and non- water based fire extinguishing system) along with standpipes and fire department hose outlets. Also have to addressed are the issues of emergency power, lighting, and exit signage. This includes: Survivability of systems Electrical Safety Distributed Energy Resources In designing the building, the incorporation of a smoke control system can significantly improve the life safety protection of the building. A Smoke Control system (sometimes known as fire ventilation or smoke vents) is to be installed. It comes in many forms and range widely in complexity, but the basic objectives are usually the same. Smoke containment systems prevent the movement of smoke and heat from one area to another. These take the form of physical barriers either as smoke curtains or fire curtains, or as pressure differential systems, also known as pressurization systems. The objectives of the smoke control system installed in the buliding are: To keep escape and access routes free from smoke. To facilitate fire fighting operations by creating a smoke free layer. To delay and/or prevent flashover, and the subsequent full development of the fire. To protect the contents of the building. To reduce the thermal effects on structural components during a fire. To reduce damage caused by thermal decomposition products and hot gases. The key components of smoke and fire ventilation systems are fire dampers; ductwork; smoke curtains; and powered and natural smoke and heat extract systems (smoke vents). The time for total evacuation by stair shafts, as currently provided, however, increases with building height and can exceed one half hour for a typical building over 20 storeys high which is the case here. Many occupants would be physically incapable of negotiating the stair shafts from the upper floors to the ground level, particularly under emergency conditions. It takes on much more serious significance for high-rise buildings because escape routes may become untenable before the occupants can be evacuated. Two important features of smoke are that it contains toxic products of combustion and reduces visibility. The two factors are generally related. Dense smoke is usually highly toxic and reduces visibility substantially. It can be assumed, that smoke will probably follow the over-all air movement within a building. The devices that can be used to control smoke in the building are as follows: SMOKE CURTAIN A smoke curtain is an automatically operating smoke curtain designed for the channeling or containment of smoke. The curtain comprises a flexible, heat resistant fabric, which is impervious to smoke and hot gases, wound round a circular tube. The tube contains an electric motor which is normally held retracted at ceiling level, and which unrolls the fabric automatically upon a signal from a fire detection system. A bottom bar is fitted to the bottom edge of the fabric to keep it taut and provide a suitable finish when the smoke curtain is retracted. FIXED CURTAINS The fixed curtains that are designed either for the channeling or containment of smoke in the event of a fire, or for sealing off an area to contain a fire and to prevent it from spreading to other areas can be used. The curtain comprises a flexible, heat resistant fabric hung from the building structure. PRESSURISATION SYSTEMS Pressurization systems protect escape routes and fire-fighting shafts against the ingress of smoke by maintaining the pressure within the escape route higher than that in the adjacent spaces. A pressurization system consists of three main components: Supply Air (where air is injected into the area that is to be protected), Pressure Relief (to avoid overpressure when doors are closed) and Air Release (air and smoke is released from the adjoining fire area). Combining these elements creates a positive pressure difference which prevents lobbies and staircases from filling up with smoke. Extinguishing agents The choice for fire extinguishers that can be used the building is varied. There can be the usage of portable fire extinguishers, safe zones, sprinklers, escape routes and fire extinguisher signs. All of them have been created to reduce the risk of suffering a fatality due to an accident. Fire extinguishers can be divided into Class A, Class B, Class C, Class D and Class K. Class A extinguishers (those that were created for combustible materials based on cellulose, like paper, wood or cardboard, or materials like cloth, styrofoam, trash or plastics. Its markings are a green triangle with an A inside and a black square with burning wood and a burning trashcan) and Class C extinguishers (those made for electrical fires. Represented by a blue circle with a C inside and a square with a burning plug and socket, they were created for extinguishing fires created within a computer, an appliance or a fuse box) are the ones most suited to our purpose. Ideally water and chemical extinguishers have to be installed in the building. Water extinguishers or APW extinguishers (air-pressurized water) are suitable for Class A fires only. They can however, be very dangerous in the wrong type of situation. Only fight the fire in case ordinary combustible materials. Dry chemical extinguishers come in a variety of types and are suitable for a combination of class A, B and C fires. Dry chemical extinguishers have an advantage over CO2 extinguishers since they leave a non-flammable substance on the extinguished material, reducing the likelihood of re-ignition. Carbon Dioxide (CO2) extinguishers are used for class B fires. They don't work very well on class A fires because they may not be able to displace enough oxygen to put the fire out, causing it to re-ignite. CO2 extinguishers have an advantage over dry chemical extinguishers since they don't leave a harmful residue - a good choice for an electrical fire on a computer or other favorite electronic device such as a stereo or TV. References: Building material, available from March 2, 09, accessed on March 24, 2009 Building Construction Techniques accessed on March 24, 2009 “Mc Graw-Hill’s Access Science” Research update, Fire safety (Building design), accessed on 24th March ’09 Plan for fire protection updated and available from November 30, 2008 accessed on March 24, 2009, Products and systems, Smoke control accessed on March 24, 2009 CBD-133. Smoke Movement in High-Rise Buildings, pub Jan 1971, (G.T. Tamura, J.H. McGuire) accessed online on March 24, ’09 Fire Extinguishers - Simple Operation, Easy Inspection, But Multiple Benefits, accessed on March 24, 2009 Classes of fire Extinguishers accessed on March 24, 2009 Read More