Enclosure Fire Dynamics - Assignment Example

pT1: Radiation Radiation can be described as the process in which energy travels through space to be absorbed by another body. Some features associated with radiation include electromagnetic wave spectrum, black body (emissive power and spectrum), opaque objects and some laws that define thermal radiation (Mahan, 2002, p. 89). Moreover, it brings into consideration view factors. Radiation usually contributes to fire spread especially due to its characteristics. Radiation is a major component that makes buildings to collapse because of fire, and also to spread fires externally. Since, the radiation process carries heat from one point to another, the heat may contribute to the spread of fire between buildings. The requirement is that the material that is utilised for external and internal lining should resist movement of radiations and hence decrease the impact of radiation associated to fires. Thus, space requirement is inherent to ensure that radiation does not take place. Radiation is dependent on surfaces; hence, the surfaces of the walls should be resistant to radiation factors. Moreover, technological advancement has ensured that materials have been developed that can mitigate the consequences of radiation. Building materials that can shield against radiation have been developed and they can be used in any building (Hancock, 2003, p. 45). T2: Enclosure Ventilation Enclosure ventilation has immersed impact on composition of smoke and on combustion. Usually, composition of smoke is dependent on conditions of combustion and the nature of burning fuel. Fire that access large amounts of oxygen burn at higher temperatures producing small amounts of smoke. On the other hand, fires with lack of oxygen burns producing wider palette of compounds (Siegel, & Howell, 2002, p. 68). The nature of combustion is controlled by the type of ventilation and hence enclosure ventilation manipulates adversely affects nature of smoke and combustion. Ventilation is an important component in any building and this means that it should be strategically located or planned. Enclosure ventilation T3: Building Geometry/ Smoke The geometry and location of the smoke in the building may determine analysis of smoke. Bringing into consideration doors, windows, walls ad may easily help in understanding production of smoke. Different types of smoke plume exist. Wall plume smoke is a type of small that follows the wall as it grows (International Code Council, 2003, p. 90). Thermal spill flume is the entrainment of air into a smoke flow that originates from a compartment opening that spills, and rises into adjacent void. Conversely, adhered spill is generated from a fire compartment that has a wall, which projects vertically and no balcony above the opening. Axisymmetric smoke plume is the type of smoke that rises above a given point source e.g. smoke rising from a cigarette. This means that the smoke moves away from the walls. Window plume comes from a compartment that has a fully developed fire while balcony spill plume originates around a balcony before rising. Generally, the building geometry shapes the behaviour of smoke, and may determine the impact of smoke on the building. It is appropriate to ensure the strategy that has been utilised ensures smoke cannot move from one room or compartment to another. Smoke is associated with numerous deaths of both fire extinguishers and inhabitants of the dwellings. Thus, measures should be in place to utilise technologies that are in place to improve on smoke management (International Code Council, 2003, p. 142). T4. Smoke Control In the case of fire incident, he products caused by the combustion usually are heat, flames, gases and smoke. Gases and smoke may bring into consideration hydrogen cyanide, carbon monoxide, and hydrogen chloride that are usually fatal to humans. Furthermore, most fatalities occur because o inhalation of smoke and gases that directs exposure to heat and flames (International Code Council, 2003). Thus, smoke control systems are used by building designers to respond to such hazards. The control system ensures that smoke is restricted from passing from one smoke “area” to another. Common smoke areas that requires utilisation of smoke control systems include floor levels, health care and detention occupancies, rated corridors, stages, horizontal exits, vertical shafts, stair entrance vestibules, exit passageways and stair enclosures (Goodfellow & Tahti, 2001, p. 1020; p. 1082). Two methods of smoke control exist, which are either active or passive. Active smoke control systems try to minimise smoke concentrations to tenable levels for enough period to allow safe escape and usually requires interaction between numerous building systems (Goodfellow & Tahti, 2001, p. 879). They usually fall into three categories, which are smoke evaluation systems, pressurisation systems, and hybrid systems. Pressurisation systems usually ensure positive pressure to keep smoke from moving from one point to another. Smoke evaluation system ejects smoke and prevents smoke from entering the building. The hybrid systems combine both elements of pressure and smoke evacuation to guarantee smoke control. On the other hand, passive method controls smoke through the use of smoke dampers and doors at smoke barriers, smoke barriers, utilising geometry and height of a space to create an area that forms a smoke reservoir. Moreover, passive smoke control systems may utilise building features e.g. doors and walls prevent smoke from moving from one zone to another. Passive protection generally utilises design of the building in creating a smoke reservoir. T5: Standard Fire Curves Standard fire curve is the simplest method to represent a fire incident through pre-defining temperature-time relationships through the use of arbitrary information. This information is usually independent on boundary and ventilation conditions (Goodfellow & Tahti, 2001, p. 98). Generally, such strategies were designed for fire resistance furnace tests of these elements and building materials for their classification and for their verification. This means that a fire resistance tests can be defined as determination whether fire protection products fulfil minimum performance requirements that are set out in a building code. An example of organisation that tests material is the Building Test Centre –British Gypsum (International Code Council, 2003, p. 67). Standard fire curves are applied differently in the case of offshore and onshore buildings. Examples of onshore building include general industry, public building and storage while offshore installations include jetties, platforms, and floating refineries. The offshore fire has a much faster rate compared to onshore fires especially in terms of initial increase in temperature (Goodfellow & Tahti, 2001, p. 989). Question 1 When T=450  = 2.75 * 1096 When T=900  = 1.34*1048 Comment =  = 2.75*1096/1.34*1048 = 2.05*1048 Question 2 Where T=20, 100, 200  = 20.023  = 100.58  = 202.31 Question 3: Diameter of cylindrical tank = Q5. T1= 293 k, pressure 1 atm and T2= 2300 k Pf= P  Pf= 1*2300/293 = 7.85 atm Laminar burning velocity Vb = Vbo (n{0.25→0.33} V=0.41(7.85/1)0.25→.33 V=3.220.25 to 3.220.33 V=1.34 to 1.47 N6: LFLi = 1/ Sum (Cfi/LFLi) = 1 / (0.3/0.05+0.2/0.41+0.25/0.04+0.25/0.125) = 1/ (6+0.49+6.25+2) = 1/14.74 =0.0678 N7. Q’ = πD2/4*Q = (3.4*2.92*500)/4 =2859.4 Lf=0.235(2859.4)0.4 – 1.02*2.9 =0.235(24.13) – 2.958 =.71255 N8 Area = 1.5 * 1.5 = 2.25m2 A = πD2/4 =√4A/π = √4*2.25/3.14 = √2.866 = 1.69 Lf = 0.235 * 23000.4 – 1.02*1.69 Lf= 0.235 * 22.12 – 1.02 * 1.69 Lf = 5.1982 – 1.7238 Lf = 3.4744 N9 D = 2.1m, Heat combustion 33.4 MJ/kg fuel, burning rate 40g/cm2s 33.4 = π2.12/4 * Q’ Q’ = (33.4*4)/ (3.14*4.41) Q’ = 133.6/13.8474 = 9.65 K/m2 Q10 Qf = Mf LV Burning rate = 40g/(m2s), Lv = 525 KJ/Kg = 0.040* 525 = 21 Kw/m2 N12 λmax = 2.9 * 10-3/T = 2.9*10-3/ 700 = 0.4143*10-5 = 4.143 * 10-6µm V = 1/λ > λ = 1/V > ¼.143 * 10-6= 2,500,000 = 2.5 * 106µm/s N13 The emissive power increases with increasing temperature at all wavelengths Eb(T) = бT4 = 5.67*10-8(2T)4 = 5.67*10-8(16T) = 9.072*10-7T N14 N15 Volume = 5*3.5*2.8 = 49m3 Area = 2*1.5 = 3m2 Mole fraction CO2 = 0.14 Water = 0.10 Soot volume fraction = 0.22*10-6 Cherry Red = 900 + 273 = 1173k L = 3.6V/A = 3.6*49/3 = 58.8 Ksoot = 258Co.T.Fv = 258*4*1173*0.22*10-6 = 0.242 Esoot = 1-e-ksootL → 14.2296 = ln 1/(1-E) → E = 0.623 Eco = 1-e-kcoL → 8.232 = ln (1/1-E) → E = 0.526 Ewater →5.88 = ln (1/(1-E)) → E= 0.435 EMixt = Egas1 + Esoot - EgasEsoot = 0.45 + 0.623 – (0.526*0.623) = 0.73 N. 16 N17 Flexible polyurethane (1390) Time = 30 minutes = ⅓RmV. Xco(%). t(min) =*4*1390*1000*50/100*30 = 1.11*107 Time = 8 minutes = ⅓RmV. Xco(%). t(min) =*4*1390*1000*50/100*8 = 7.4*106 References Goodfellow, H. & Tahti, E. 2001. Industrial ventilation design guidebook. London: Academic Press. Hancock, G. 2003. Advances in structures: proceedings of the International Conference on Advances in Structures. Sydney: Balkema. International Code Council. 2003. International building code 2003, 2nd Ed. Michigan: International Code Council. Mahan, J. (2002). Radiation heat transfer: a statistical approach, 3rd Ed. New York: Wiley-IEEE. Siegel, R. & Howell, J. 2002. Thermal radiation heat transfer, Volume 1, 4th Ed. London: Taylor & Francis. Read More