BS 7974:2020 Application Of Fire Safety Engineering

Added on -2020-02-19

| BS 7974 Application Of Fire Safety Engineering| 12 pages| 3928 words| 203 views

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RUNNING HEAD: FIRE ENGINEERINGINTRODUCTIONWith the structural developments in existence at the moment, buildings are growingmore and more complex. With some growing taller, a lot of them are also growing interms of area occupied laterally making them more and more complex. With this, it isbecoming harder to be able to protect and safely account for people occupying thesebuildings were a disaster to strike. While relevant codes of construction have givenenough advice on construction techniques, no one standard has provided fordisaster management. While some practices during the operation of a building’sfunction may be controlled to reduce such risks, it is impossible to out-rightly comeup with codes provide construction methods that totally protect against these naturaldisasters [1].Among these disasters is fire which can be a result of natural causes or a result ofhuman error. Fire in buildings is among the most dangerous disasters leading to thesecond largest percentage of deaths caused by elemental disaster. This is primarilybecause fires cause fatalities owing to the smoke, chemicals, fire damage and theheat itself [2]. In most cases, fatalities during fires occur mainly because the victimsin these fires were trapped and could not get out in time. While obstruction is a majorcause of trapping, smoke inhalation is also a huge factor leading to individuals beingtrapped because the smoke, apart from obscuring the paths to egress points, alsohas compounds which are poisonous to the human lung [3].This therefore necessitates the evaluation of the Required Safe Egress Time (RSET)and the Available Safe Egress Time (ASET). This time is important as it helps indirecting occupants in any evacuation procedures in the case of a fire hazard inoffice spaces, industrial buildings, residential structures or any generic enclosurewhere occupant’s evacuation in case of a fire should require prior planning [4]. Theevaluation is usually carried out by taking and comparing some severalpredetermined or stochastic performance criteria, analysing the duration taken forevery considered element to reach the established threshold limit and this is done forevery one of those preselected criteria [5]. Computational fluid dynamics (CFD)testing was done using a Fire Dynamic Simulator (FDS) model which presents anASET performance criteria [6]. A comparison between the values of a quick1
RUNNING HEAD: FIRE ENGINEERINGestimation of the ASET results and those of the computer generated FDS results inan analytical assessment of the conditions in enclosure shown is documented below.The building being tested is a warehouse mezzanine floor space. This space is notconsidered to be a storage facility and in coming up with the values, an assumptionwill be made that the percentage of the room occupied with highly flammablematerial is 0 - 10%. With this assumption, we can assume that very little to no toxicitywill be encountered courtesy of the stored material [7]. The building complexity willbe taken as class B1 as warehouses are, in most cases, plain and open in order tomaximize on storage space [8]. The alarm level will be A2. This is assumedbecause, owing to the fact that the building is a warehouse, protection of goods fromfire hazards is of paramount importance [8].A management level of M1 will be considered owing to the assumption that all staffand occupants of a warehouse premises have some degree of training on fireemergencies owing to the high safety level of environment expected in a warehouse[8]. This is assumed because of the industry regulations involving occupant safety inindustries, construction sites and warehouses. This indicated that the response andevacuation time for the staff will be relatively quick. Firefighting equipment is alsopresent in warehouses as a regulatory measure and thus any obstruction due to firesand smoke will be cleared by the trained staff [8].For the ASET analysis, a tenability criteria is derived from assuming the maximumlevel of exposure to the fire hazard that the warehouse personnel can tolerate fromthe fire without being incapacitated. From the CIBSE guide E, we see the growth rateof a fire in a warehouse characterized as ultrafast [9]. While this is a mezzanine floorwith possibly little storage facilities and hence low storage capacity, and while theCIBSE value is still dependent on the load, the worst case scenario is that of a firespreading from the storage area or starting at the mezzanine and spreading to thestorage area. With that information, the time taken will be 75 seconds while theconstant α is 0.1876 kW/s2 [9]. The mezzanine floor’s dimensions are 100m in lengthon each side, making up an area of 10000m2.The tenability criteria that were used in this analysis were derived from theassumptions that a minimum smoke-free layer height of 2m above the floor would beprovided for and that a maximum upper layer temperature of 200C would be felt by2
RUNNING HEAD: FIRE ENGINEERINGthe occupants. The warehouse’s occupants were assumed to be capable of rapidphysical movement and willing and able to evacuate the floor in clear air under sucha smoke layer. The downwards heat radiation value was also considered tolerablefor the occupants [10]. A ventilation system is designed in the FDS model and will beused to help divert the smoke away from the ground and allow some clean air tocome in under the smoke layer thus enabling the height of the smoke free layer toremain constant even as smoke increases. The ventilation system consists of 4exhaust vents and 2 make-up vents.To conduct the ASET, some values in the ASET equations and tenability criteriahave to be assumed in order to develop a characteristic model. The assumptionhowever should, however be made as relative to the model as possible. For thisproject, a visibility distance of 10m has been assigned as the space is large (100meters on each side) and the floor has minimum complexity. This will affect theresponse time and evacuation time in the building. It is also assumed that, while notmany details are known, the calculations based on worst case scenario assumptionshould work in this floor in order to prepare the best safe evacuation margin. Theformula for ASET is given below;ASET(t)=Cef3tg25H45¿Where;Cef3 = 0.937,H = the minimum smoke-free layer heighttg = growth timeA = Area of the roomZ = height of the first indication of smoke that can be noticed above the fire.The formula for z is as shown below:z=0.20Qp2/5Where Qp = the convective heat fire output. The values of Qp is given by Qp=Q/1.53

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