Fires in Buildings - Case Study Example

Fire in buildings Introduction Fire is a chemical reaction that releases energy. It is called exothermic chemical reaction. “Joules” is the unit of measurement of the energy. It is measured as joules per second (J/sec) or Watts (W) The energy radiated over an area is called radiant heat flux and identified as kilowatts per square meter. (KW/m²) For a burning to take place all liquids or solids must transform into gases by vaporisation or decomposition. (Lentini J and Lentini L, 2006) The built structures are equally susceptible to fire as forests and fields are. Designing of the hearth, house or town cannot afford to ignore fire possibilities. Buildings are more prone to fire than the fields around them since crowding of people increases the fire density and structures tend to pack fuels. Behaviour of fire depends up on the terrain, fuels and wind present in the buildings’ environment. It can start from a spilled candle or a lightning bolt. Control of fire is characterised by extinguishing the flames, removing the fuels from the site of fire and setting backfires. The building must be designed not to burn so easily and not to make fire to spread even if kindled. The building should have architectural firebreaks for containing the fire that spreads. The fire in a room behaves like a hearth fire than a forest fire in that just like a candle placed in a box , a fire in a closed room will absorb the oxygen inside the room and later convert into ready-to-combust gases while the heat will dissolve fuels into vapours and gradually die down unless a fresh air enters the room. On the other hand, if there is more oxygen inside the room without fully being devoured by fire, and if the heat radiating from the gases exceeds the ignition temperature of the room surface, all will burst into a flame. Or if the oxygen enters the closed room through a door or window forced open, the mix of the trapped gases will explode. Thus, main reason for fire behaviour is the airflow. Just as wildland flame travels with the wind, room fire travels along the ventilation flow within a building. Fire behaviour can be controlled in such situations by widening the vents and making a hole in the roof to direct the rate of combustion or reduce the possible backdraft. Water can also be used to control fire when poured or shot into the room and it then becomes steam by absorbing the heat inside and spreads out just as combustion gas does. This control is not possible in wildland or agricultural landscapes. Therefore, fire resistance or protection depends on the confinement of fire into a single room or set of rooms designed accordingly. Nevertheless, fire will not stay in single rooms and can spread among the surrounding buildings. (Pyne, 2001) One of the fourteen requirements for whole building performance defined by The International Standards Organisation is fire safety. It should be an integral part of performance design due to interactive nature of the fourteen requirements. Many a time this fire safety requirement as an intangible benefit is not realised unless real fire emergencies occur. (Marchant, 1985) The fourteen requirements are ….stability, fire safety, safety in use, tightness, hygrothermal, atmospheric, acoustic, visual, tactile and anthropodynamic, hygiene, spatial suitability, durability and economy.(Marchant, 1985) Since each of the above requirements interacts with all others, fire safety will depend upon all other requirements also for the building performance. For instance, interaction between tightness and hygrothermal aspects promote condensation which will have a second order impact on fire growth. There are regulations in the U.K. in respect of fire safety in buildings. In respect of Internal Fire Spread (surfaces), it has been stated that in order to prevent fire spread within the building, materials used as finishes for walls and ceilings and in cavities shall be resistant to ignition, shall reasonably also resist the spread of flame over their surfaces, and shall not release excessive rate of heat release on ignition. In respect of internal fire spread (structures), the stipulation is that construction of buildings should be in such a way as to maintain its stability when fire occurs in it. And that the building should be subdivided into compartments according to its use to prevent spread of fire from one compartment to another. Concealed spaces should also be properly enclosed so as to prevent unseen spread of fire and smoke.(Marchant, 1985) USA CASE STUDY The Roc Harbour Town House Complex fire, New Jersey The fire started at 1:00 pm when the temperature was 50°F and wind was blowing at a speed of 10 mph. The Roc harbour is woodframe town house complex situated on the banks of Hudson River. It is gated complex and is crescent shaped. At the time of arrival of the fire fighting team, fire and smoke was billowing out of the third floor on the south west side of the complex. The fire unit had to pancake the roof and all the floors up to the garage. However, the fire did not travel beyond the point of origin. The attached units of the buildings were also saved. Two factors contributed to the success of the operation. One was effective apparatus positioning in the initial stages of the operation and the other was aggressive and hard fought battle waged by the fire fighting teams to keep the fire confined to the point of origin. This however was possible due to timely arrival and access and positioning of the equipments and personnel though at an incredible speed. (Avilo, 2002) LONDON CASE STUDY HERON TOWER The tower is of a real high-rise design. It is subdivided into three storey blocks known as villages. They are connected internally by an atrium. The northern, western and eastern sides are covered with glass windows. Southern sidewall is an interior wall. Each village is of measurement 50 x 25 m² with 3 m high ceiling. The atrium has 1250 m² surface area on each floor with glazed facades and is not within the permitted ranges of the codes. Heron Tower is an office complex and assumed fuel load is 25kg/ m² of cellulose type with a heat combustion of fuel to be 16 KJ/g. The mass burning in a typical office building is 20 to40g/ m² s¹¹ and the relative heat release per unit area will be from 320 to 640 KW/ m². Simulations were carried out in order to ascertain the fire dynamics in the buildings that are built outside the code ranges. (Rein et al, 2007) The study looked at both well-distributed and travelling fires. The analysis indicates that a travelling fire through the bottom of the atrium leads to marginally lower temperatures than a uniform fire all over the floor. However, the spreading process can result in a much longer fire and thus could be considered a worse scenario than a well-distributed fire. Comparison with the standard fire curve shows extreme divergence respect to the travelling fire curves after 1 hr of burning time. The standard curve is shown to extend into a temperature/time range that cannot be explained in terms of fire dynamics. Comparison to the parametric fire curve used in the Heron Tower structural design shows agreement with the 600 m2 travelling fire captured by our methodology. The meaning of this agreement needs to be further investigated.(Rein et al, 2007) JAPAN CASE STUDY Analysis of Fire and Evacuation in a Multi-purpose Office Building, Osaka, Japan A fire took place on April 4, 1984 at the Science and Technology Centre of Osaka housed in a multipurpose office building occupants of which were regular users of the building except those used the assembly halls. Purpose of this study was to serve as guidance for future evacuation of multipurpose buildings types of which have become common in later years. The survey on the fire conducted among the people who were present at the building during fire highlighted the difference in perceptions between the regular users and infrequent users of the building. The difference was in respect of action taken by them on coming to know the fire, the manner of selection of escape routes and the successful exiting the building. There were eight floors in total apart from three sections of basements. Total number of occupants was 679, number of evacuees was 577 and the rest 102 persons were rescued by window. Floor area was 12,485 m² and burnt area was 473 m². The survey was taken two weeks after the fire incident with 23 questions and distributed among 679 persons who were at the Science and Technology centre. 458 of them alone returned the questionnaires. .(Grant and Pagni, 1986) Analysis Date and time were April 4, 1984 and time 11.25 am approximately. Location of fire was at 3rd floor at the hallway near the western stairs. The burnt areas were 473 m² of the 3rd floor, 62 m² of the ceiling surface of the third floor and 88 m² of the exterior wall surface of the 4th floor. Totally 8 person injured because of carbon monoxide poisoning and they were all alive. Cause of fire was suspected arson. The building was 8 stories high of reinforced concrete with the facilities such as elevators, stairs and lavatories at the centre core. There were also enclosed stairs on the eastern and western corners of the building. The enclosed stairs fitted with fire doors that had been kept closed. Users of the third and fifth floors were regular occupants of the office premises therein and those who were in the fourth and sixth floors at the assembly halls therein were newly recruited employees undergoing training sessions. They were not familiar with the building. Similarly, there were also people at the seventh and eight floors attending conferences who were infrequent visitors though they had visited the building on earlier occasions. . (Grant and Pagni, 1986) Discovery of fire On hearing an explosive sound at the third floor, an employee working therein rushed and found hallway floor and west stairway in flames and the ceiling covered by smoke. Another employee in charge of fire prevention from the same floor while asking asked another one to bring the fire extinguisher, rushed to the security office at the first floor and asked security officer to alert the fire department. He also alerted all floors through public address system asking the occupants to avoid central stairway and evacuate through east or west emergency stairways. The fire department noted the time of report of fire as 11.32 am. Fire services arrived at 11.39 am along with fire fighters. The smoke was coming out of the window of the floor. Many employees came out by themselves to the streets and surrounded the building. Those who could not evacuate from the 3rd and 6th floors, were waving their hands trough windows. . (Grant and Pagni, 1986) Spread of smoke Since the fire shutters for the central stairway had not been closed, smoke spread to the top floors. The occupants of the third floor reported not having seen heavy smoke, probably because they had already discovered the fire much earlier. . (Grant and Pagni, 1986) Awareness of fire Occupants reported coming to know of fire by various means such as seeing the fire, smell, explosive sounds, announcement over the public address system, yelling of others, on seeing smoke at the corridors on opening the doors, when smoke entered their room, alerts from seminar leaders, alerts from other and still other means. . (Grant and Pagni, 1986) Conclusion Regular users of the building have demonstrated that they will act in many ways in response to fire including attempting to put out fire, alerting people and helping them to evacuate. Those who are not familiar with the building, the tendency would be to evacuate immediately. The evacuation routes chosen evacuees depend on the density of smoke seen. However, sex, job and familiarity play important roles. Evacuation routes will be the usual routes for those already familiar with the building. Those who are not, will generally follow or take others’ advice. Familiarity with the building will enable the occupants to make exit even in thick smoke. For those not familiar, exiting is of great difficulty. Familiarity with the building is the sole determinant for the speed and ease with which evacuation can be achieved. (Grant and Pagni, 1986) SPAIN CASE STUDY WINDSOR TOWER FIRE CASE STUDY The fire that occurred at the Windsor Tower in Madrid on February 12-13, 2005 and lasted for 18-20 hours causing extensive damage to the structures of the upper floors. The concrete structure of the building with steel content without fire protection would cause severe damage. Damage occurred to floors 17-28 which lay above the transfer floor (T) of the building. It was found that perimeter steel columns at this height were not fire protected. As the columns lost strength, they could not serve as cantilever any longer resulting in their progressive collapse. Northeast corner of corner of the building collapsed at 01:15 hrs. There was no damage to the new fire escape on the west face due to additional support to the floor. In spite of a fully-flashed over fire for a long time after 06:00 hrs in the morning, concrete slab on the floor 9 did not suffer significant collapse. There was also no fire protection on two sides because of which steel columns also had undergone sever buckling. Because of the load sharing and support coming from protected steel columns above and below, contributed to the over all stability of structure. Fire occurred at 23.05 hrs on the floor no 21 in office no 2109 which was detected within 3 minutes at 23.08 hrs. The flame was reported seen at 50cm by 23.18 hrs within 13 minutes of fire breaking out and the fire was characteristic of waste-basket fire source. The fire brigade was called in 23.21 hrs and by 23.35 i. e within 30 minutes of breaking out, the 21st floor was fully flashed over. Once the fire established itself, the rapidity with which it spread from floor to floor demonstrates the mechanism of fire spread. Although it was initially over estimated at 00:00 hrs of rapidity, the spread rate varied from 6.5 minutes to 15 minutes per floor. Burning histories show that, the spread took 40 minutes to reach 22nd floor from the 21st floor and 70 minutes to 23 rd and 24th floors and only 30 minutes to the reach the top most 28th floor. National Scientific Police gave another estimate of 10 minutes per floor for the upward floor. Some inherent structural weakness in the glazed curtain walling systems could allow the fire to spread from floor to floor in various mechanisms. . (Fletcher, Borg, Hitchen, and Welch) Though there is no reason to suspect that fires are any more likely to develop in buildings with glazed facades, the tendency for substantially greater consequential loss per fire is a concern to insurers; this fact is clearly exacerbated when such fires lead to structural failures of major part of the building, as occurred in the Windsor Tower, with the costs of repair greatly increased. It is hoped that by better understanding these types of fires, and the behaviour of concrete structures, these types of losses could be minimised in the future. (Fletcher, Borg, Hitchen and Welch) Conclusion The case studies give a wide range of possibilities of fire scenarios including simulated one. Fire behaviour depends on the aggravating conditions like wind, fuel package and its severity and its after effects can be mitigated by proper designing of the buildings and precautionary steps for fire fighting in an eventuality. References Avilo Anthony, 2002 “Fireground Strategies: Fire Engineering” PennWell Books, 2002 p 287-294 Grant E Cecile and Pagni J Patrick, 1986 “Fire Safety Science: Proceedings of the August International Symposium’, Taylor and Francis, p 523-532 Fletcher Ian, Borg Audun, Hitchen Neil, and Welch Stephen, “Performance of Concrete in Fire: A Review of the State of the Art, with a case study of The Windsor Tower Fire” available accessed 11 December 2008 Lentini J. John, Lentini L, John 2006 “Scientific Protocols for Fire Investigation” CRC Press, p Marchant, 1985 ”On fire performance standards” in Harmathy T.Z. Fire Safety, Science and Engineering: A symposium ,ASTM Committee E-5 on Fire Standards, ASTM International p 10,11 Pyne J Stephen, 2001,” Fire: A Brief History “Jeremy Mills Publishing. p 102-106 Rein Guillermo, Zhang Xun, Williams Paul, Hume Ben, Heise Alex, Jowsey Allan, Lane Barbara, and Torero L.Jose, 2007, “Multi-Storey Fire Analysis For High Rise Building”availableaccessed 5 December 2008 Read More