Zone Modeling in Fire Safety - Research Paper Example

Q1. Explain and compare zone modeling and CFD in fire safety. CFD: The field models of fire safety study are called as CFD - "Computational Field Model". To understand the concept let us discuss the model. The velocity of gas in a room at a particular moment of time is a vector having speed (magnitude) and direction. If we mark all such gas velocity vectors with arrow vectors, a picture will look like a wind blowing over a field of grass. That's why such models are termed as field models. In CFD, any physical quantity, which has magnitude and direction, can be termed as a field. The examples of field are pressure, momentum, velocity etc. The physical variable such as density, temperature can also be termed as field and it can be represented by a field equation. These field equations are solved with the help of computerized programs. The modern day computers can solve many of such field equations simultaneously. The calculations of fluid flow are very lengthy and are beyond the calculation capacity of normal human. That's why these field equations are solved using a computer which signifies the name CFD. All the variables in a room are modeled at a given point of time. To model all the basic physical and chemical variables, it will require computer with very high computational power. Now days, it has become possible with the advancement in computer technology and use of such computer programs on rental/subscription basis. Even expert advice can be made available on a phone call. Zone Modeling: The zonal model divides the fire compartment into different group of zones. The models are prepared to evaluate the interactions of mass and heat transfer between the zones. Standard zone models are already in practice but still new models are coming up. Considering a zone model in a single room, the concerned zones can be the burning object, the flame, the heat layer, the cold layer, the openings (vents), other objects - which are not ignited yet, and the walls/boundaries of the room. The important physical interactions between zones can be analyzed. It can be observed that the heat is transferred to the burning object from the flame, from the boundaries and from the upper layer. The heat thus received by the object causes it to undergo pyrolysis and mass are transferred to flame. This type of relational model is developed for each zone. There are a set of equations in a zone model which describe the interaction between the zones. Several zone models are available depending on the scenario. Some zone models are designed for a single room fire on the contrary others are developed to depict the fire and smoke movement in the entire building. From the above discussion it is quite clear that CFD model depends on the computer programs and the approximations in it. There are huge computing requirements, which are not easily available. Even though there are errors in this models due to lack of exactness of data and approximations, still it is quite useful to project the deterministic fire model. Zone models do require the mathematical calculations for spread of heat and smoke but they are not as complicated as the CFD models. Comparatively zone models are simple but require sufficient information as the input data. Insufficient and inaccurate data can project an erroneous simulation. Zone models are quite popular and standard zone models are readily available. Q2. In a fire experiment an 80W light bulb is used in an emergency exit sign and a light detector placed across the room registers 3W. The room is 3 m across and smoky hydrocarbon fire is used in the experiment. What is the visibility and what is the obscuration Solution: As per data given in this example: Intensity of bulb = = 80 W Intensity of light as received by the detector = I = 3 W Distance between the bulb and light detector = length of room = L = 3 m Obscuration = S = S = 96.25 Optical Density of Smoke = D = D = D = D = 14.2 dB Now visibility: (For luminous objects) 5.28m Q3. What is the compression ratio of an engine and why is it useful The working of the Internal Combustion (IC) engine is based on four strokes. 1. Suction or Induction stroke 2. Compression stroke 3. Burn or Power stroke 4. Blow or Exhaust stroke During the above operations, the power stoke gives out the thrust for the rotation of the fly wheel. The amount of thrust is dependent on the effective burning of the fuel. For proper burning of the fuel preheating is necessary. The compression stroke offers the preheating of the fuel. The volume of the combustion chamber according to the position of the piston decides the quantum of preheating offered to the fuel before combustion. "The ratio of the volume of the combustion chamber when the piston is down to the volume when the piston is up is called as the compression ratio." The higher compression ratio signifies more preheating and also justifies pouring of more air into the combustion chamber. Higher compression ratio augments the power of the internal combustion engine and also enhances its efficiency. Q6. In a 10m*8m room 3m tall there is a mock-up sofa consisting of 32kg chipboard with 9 kg PVC cover and two 2kg cushions made of (and covered with) cotton. What will be the visibility in the room if this all burns 100% in the flames but 90% of the smoke leaks out of the room Solution: As per the given data: Volume of room = V= The constituents of the mock sofa: Clipboard = 32 Kg PVC = 9 Kg Cotton Cushions = 2 Kg It is stated that burning of all the material has been taken place 100%. That means all the material has been converted to flames. Smoke loading - R (/Kg)- flaming for the above materials are: Cotton = 140 /Kg PVC = 393 /Kg Clipboard = 370 /Kg The visibility can be calculated as per the formula: Now the total smoke generated after 100% burning of all the material is : 15657 But 90% of the smoke leaks out of the room. That means only 10% of the smoke remains inside the room. Therefore amount of smoke present inside the room = = 1565.7 Read More