Built Environment : Physics Equations - Assignment Example

FV2003 FIREAND THE BUILT Assignment Part One common thing about builders, developers and commercial property owners is their dread of a devastating fire. Indeed, it is very simple for a fire to start. All that is needed is a 'heat source or spark, some flammable material, and a few minutes of inattention for livelihoods-and lives-to go up in smoke'.1 The kitchen is where fires usually start, either in homes, hotels or restaurants. But no matter where a fire commence, it is very important to do some fire preventive measures starting from the construction of a house or a building. To start off, building construction methods and materials to be used are selected wisely and sensibly. Let us imagine that we are to design an intelligent building, 20 storey block, multi-occupied premises (50% - hotel and 50% - offices), in the city centre of Preston. A 'fire-resistive' building type (Type I) is to be used in the design. Structural components of this type of building are that all roofs, walls, floors and supporting members ought to be made of non-combustible material; these materials are those that 'will not ignite, burn, support combustion, or release flammable vapours when heated'. Structural elements such as 'bearing walls, columns, beams, including girders, trusses, roofs and floors' may incorporate concrete and steel technology.2 Walls within hotel and office rooms can be constructed with the following: Light steel infill walls provide the external envelope and compartment walls between roomsand the cladding to all buildings are a combination of a metallic cladding panel and a lightweight terracotta tile system which are attached to horizontal rails screwed through the external insulation to the light steel infill walls. Light steel C sections provide the required resistance to wind loads and support the self weight of the cladding. The internal compartment and partition are designed to give excellent acoustic insulation and fire resistance properties when finished with two layers of fire resisting plasterboard per side. Fire protection is achieved using intumescing coatingand the lightweight metallic and terracotta tile cladding system is selected in order to create a desirable architectural appearance.3 Non-combustible materials which are subject to stress from high temperature, such as steel should be protected from heat to prevent them from expanding which can result to structural failure. In order to boost the fire safety of the building, the following systems may be or must also be incorporated in the building design4: 1. Smoke Management and Control Smoke management system is important in order to 'modify, dilute or redirect the movement of smoke' in a burning building, thus facilitating evacuation. Smoke control system, on the other hand, is utilized to 'limit and control the movement of smoke during a fire'.5 The following may be used as a smoke control system in our design: The most common approach involves pressurizing the areas on either side of the compartment where the fire is located and exhausting the fire area. This method creates a 'pressure sandwich' which tends to move air (and thus smoke) from the protected areas towards the fire and move smoke out of the fire area. While this does introduce fresh oxygen to the fire area, most systems are aimed at protecting the occupants and equipment in the adjacent compartments to allow evacuation and to allow firemen to gain clear access to the fire to extinguish it. The fire management techniques, equipment, and constructions employed around the fire compartment are relied upon to contain the fire rather than smother it by denying it air, which often will increase the smoke generated.6 2. Fire Sprinklers and Extinguishing agents A fire sprinklers together with a fire extinguisher must be installed in every room in the building. The Metasal 876 is an excellent choice of extinguishing agent. It is multi-purpose, which means it can extinguish fire classes A (fires of solid organic materials which burn forming glowing embers), B (fires involving liquids or liquefiable solids), C (fires involving gases), and D (fires involving metals).7 It is 'also suitable for use where there is electrical current and in the correct extinguishing apparatus, it is also suitable for extinguishing aluminium and magnesium alloys'. Metasal has been 'developed for all those situations where it is necessary to cover all types of fire with the maximum possible security'.8 3. Standpipes and fire department hose outlets 4. Fire detection and alarm 5. Means of egress (i.e. exit stairway, areas of refuge, and accessibility of fire exits) Except for having an excellent fire protection scheme, it is necessary that it should harmonize and synchronize with other building systems (i.e. structural) and overall building design to optimize safety. Part 2 - Solve the following fire modelling problems. 1. Find the flame height of the fire involved plastic materials of 0.3 m2 circle area with burning rate approximately 10.5 g/s at a heat of combustion of 23kJ/g. What should be a critical diameter of the fire area that the fire reaches ceiling on height of 2.5 m Flame Height (L) Critical Diameter (D) 2. Mixed fuel is composed by methane (volume percent is 0.55), carbon monoxide (0.25) and hydrogen (0.20). Calculate the lower flammable limit concentration for the mixture and the concentration of each component in the mixture with air. Given the following: Name of Gas Volume Percent (C) Lower Flammability Limit (LFL)9 Methane 0.55 5 Carbon Monoxide 0.25 12 Hydrogen 0.20 4 3. Consider a 1 m diameter pan fire of petrol with heat release intensity of about 400kW/m2 of surface area. Calculate the flame height under the normal atmospheric conditions. Flame Height (L) 4. Calculate the wavelength for infrared thermal radiation with frequency 1014Hz and compare with the wavelength for BBC Radio 4, 93.0 MHz (Preston). Wavelength for BBC Radio 4 The wavelength for infrared thermal radiation with frequency 1014Hz is which is approximately 1,000,000 times smaller than the wavelength for BBC Radio 4 frequency (93.0 MHz). 5. A person with initial speed of 1.15 m/s is moving to fire exit as described on the Fig. 1. Histravel consists of two parts (AB and BC). In the first part (AB) he is moving with constant speed of 1.15 m/s. When he has achieved the point B, he will start to move with constant deceleration of 0.01 m/s2 due to the crowd in the second part of his trip. What time is needed for the person to achieve the fire exit Assume that AD is 7 m, BC is 8 m and = 30o. Let: - Time needed to travel from point A to point B - Time needed to travel from point B to point C (fire exit) - Time at point B - Time at point C Find for AB: Find for: Find for: Find for: Finally, find the total time to reach the fire exit: 6. A person is moving to a fire exit through a corridor (Fig. 2). His speed is 1.1m/s and constant during his travel. In the corridor there is a strong air movement. Speed of air movement is 0.3m/s and width of the corridor is 12 m. Find the minimum time needed to reach the fire exit. Explain your answer and indicate the right direction for his evacuation Find for: Find for AC: Find for: The time is the minimum time needed to reach the fire exit. The person should evacuate towards the direction of an angle approximately 20 degrees towards the fire exit at a speed of about 1.1402 m/s. 7. How different is the result for the previous question, if air movement changes its direction on opposite (U = - 0.3 m/s). Find for: There is no difference for the computed final velocity, for U = - 0.3 m/s or U = 0.3 m/s. The direction of evacuation, however, may vary from +20 degrees to -20 degrees towards the fire exit with respect to the corridor AB. 8. Compare the chemical reaction rates at three temperatures - 300, 600 and 900 K. The activation energy is 120 kJ/mole. Make your conclusion how temperature affects chemical reaction rate. "The only way to explain the relationship between temperature and the rate of a reaction is to assume that the rate constant depends on the temperature at which the reaction is run. In 1889, Svante Arrhenius showed that the relationship between temperature and the rate constant for a reaction obeyed the following equation. In this equation, k is the rate constant for the reaction, Z is a proportionality constant that varies from one reaction to another, Ea is the activation energy for the reaction, R is the ideal gas constant in joules per mole Kelvin, and T is the temperature in Kelvin."10 At T = 300K: At T = 600K: At T = 900K: "The rate of a reaction depends on the temperature at which it is run. As the temperature increases, the molecules move faster and therefore collide more frequently. The molecules also carry more kinetic energy. Thus, the proportion of collisions that can overcome the activation energy for the reaction increases with temperature."11 9. A compartment is fully involved in fire. The flame inside the room is dull red. Calculate thermal radiation emission [W/m2] from the compartment considering the gray body model with = 0.8. 10. Explain nomenclature of halon and Freon systems (use examples of Halon1211 and Freon CFC 11). Make a definition of environmental damage potential of halons and freons. Compare environmental damage potentials and atmospheric lifetimes of Halon 1211 and CFC 11. The CFC naming system was developed by T. Midgley, Jr. and A. L. Henne in 1929. Further refinements were made by J. D. Park soon after the CFC naming system was established. "Full details of the nomenclature system are specified in ANSI/ASHRAE Standard 34-1992 with additional annual supplements. Chemical names are frequently used in place of the numbers for common materials - such as trichloroethylene and chloroform. The specified ANSI/ASHRAE prefixes were FC (Fluorocarbon), or R (Refrigerant), but today most are prefixed by more specific classifications - such as CFC, HCFC, and HFC." Take for example the CFC 11. CFC-11 CCl3F trichlorofluoromethane [75-69-4] Another method for naming CFCs 'uses the addition of 90 to the CFC number to produce a "def" number which corresponds to the CHF composition. If (e + f) < (2d + 2), then additional atoms are required for saturation'. For instance: ASHRAE +90 Empirical Composition Formula C H F (+Cl) CFC-11 101 1 - 1 3 CCl3F The US Army Corps of Engineers developed a completely different naming system for halons. Hydrogen is not numbered, and terminal zeros are not expressed. Halon-0123 where 0 = number of carbon atoms 1 = number of fluorine atoms 2 = number of chlorine atoms 3 = number of bromine atoms Consider for example Halon 1211: Halon-1211 CBrClF2 bromochlorodifluoromethane [353-59-3]12 'Halon is a liquefied, compressed gas that stops the spread of fire by chemically disrupting combustion'. Halon 1211 (a liquid streaming agent) leaves no residue and is remarkably safe for human exposure. Halon 1211 has 'low-toxicity, chemically stable compounds that, as long as they remain contained in cylinders, and is easily recyclable'. Halon has been used for fire and explosion protection throughout the 20th century, and remains an integral part of the safety plans in many of today's manufacturing, electronic and aviation companies. Halon protects computer and communication rooms throughout the electronics industry; it has numerous military applications on ships, aircraft and tanks and helps ensure safety on all commercial aircraft. Halon is a CFC, thus production of new Halon ceased in 1994. There is no cost effective means of safely and effectively disposing of the Halon. Therefore, recycling and reusing the existing supply intelligently and responsibly to protect lives and property is the wisest solution.13 "CFC-11, also known as trichlorofluoromethane, Fluorochloroform, Freon 11, CFC 11, R 11, Arcton 9, Freon 11A, Freon 11B, Freon HE or Freon MF was a refrigerant used in operating systems before its ban in 1995. Its chemical formula CCl3F reveals that it is a chlorofluorocarbon, a compound with fluorine (F) and chlorine (Cl) atom attached to the central carbon. What made CFC-11 so harmful to the environment is its ozone-depleting potential of 1.0, on a scale of 0-1. CFCs are very stable in the troposphere but when CFC-11 hits the stratosphere UV reacts with chlorine atoms in CFC-11 that then react with ozone and initiate cycles that deplete the ozone layer. When this compound is exposed to ultraviolet (UV) light in the stratosphere, chlorine atoms are displaced and CFC-11 splits into CCl2F (gas) + a single chlorine (Cl) in gaseous form. This chlorine atoms reacts with ozone (O3) splitting it to form ClO (gas) + O2 (gas). Since there is a plethora of ozone molecules in the stratospheric layer due to photochemical breakdown of ozone, CFC-11 has the potential to destroy many ozone molecules."14 Finally, 'on January 1, 1996 the ENVIRONMENTAL PROTECTION AGENCY stopped the production and use of all class 1 ozone depleting substances' including CFC 11.15 Read More