Reference no: EM132322724

 

Question 1
(a) Describe the "fire triangle" and discuss the importance of each element in the combustion process.

(b) In your own words explain what "Activation Energy" is. If two polymers had different activation energies, which one would be easier to ignite? Explain why.

(c) If the Heat of Combustion of Benzene (C₆H₆) is 4.25MJ per mole; How much heat can I expect to be released if I burn 100g of Benzene knowing that the Combustion Efficiency is only 80%. Show your workings.

Question 2
(a) In your own words explain what is the relevance of the "Thermal Diffusivity" of a brick to the temperature measured on the hot side of a brick wall heated on one side.

(b) Calculate the conductive heat transfer rate through a concrete slab of 250 mm thickness where the bottom is exposed to a temperature of 600°C and the top is at ambient conditions. where ambient temperature is 20°C

(c) If a "Black-body Radiator" was at a temperature of 950°C, how much radiant heat energy would it be emitting over every square metre of surface area?

(d) A steel plate is exposed to a fire-source-feature on a neighbouring property and receives a radiant heat flux of 65 kW/m². Assuming the steel plate has an emissivity of 0.8, what temperature would the plate heat up to?

Question 3
(a) Hot gases at 600°C from a fire are flowing past a plasterboard wall whose exposed surface has already been heated to 200°C. How much convective heat energy is transferred from the hot gases to the wall per square metre if the heat transfer coefficient is 15W/K m²?

(b) From the question above, if the effective emissivity of the hot gases is 0.8 and the emissivity of the plasterboard wall is 0.9 in the above question, how much net radiant energy is transferred per square metre to the wall?

(c) A room with a flashover fire has a window 1.8 m high and 2.4 m wide which is emitting radiant heat at a mean value of 149 kW/m². What is the maximum radant heat flux that would be received at the property boundary 1 m away assuming that the window is a black-body?

Question 4

(a) A fire is burning near the corner of a 5mx5m room having a ceiling height of 3.0m. The fire is ventilated through an open doorway where hot gasesflow out of the room and cold air flows into the room. There is an upholstered lounge suite in the middle of the room that can be assumed to ignite in a relatively short period of time when exposed to a radiant heat flux of 18kW/m². What temperature would the hot gases beneath the ceiling need to be for the lounge suite to ignite? Assume that the hot layer has an emissivity of 1 and that the hot layer is 1.2m above the top of the lounge suite.

(b) Compare your answer with the following statements:

a. "A temperature between 400 and 600°C of the hot layer gases is likely to result in flashover in acompartment."
b. "Flashover is likely to occur when the tip of the flames reach theceiling".

Question 5

(a) Plot the heat release rate of a fire that has the following characteristics:
i. Initial growth as a t2 fire at a rate that achieves a convective heat output of 1.5 MW after 150 seconds until sprinkleractivation.
ii. Sprinklers activate when the total heat release rate of the fire has grown to 3MW.
iii. The sprinkler system has been designed to an "Ordinary Hazard" occupancy with a discharge density of 0.08mm/s. Following sprinkler activation the heat release rate of the fire follows the "NIST" equation fore sprinkler suppression.

(b) Discuss the following with respect to a sprinklersystem:
i. Required DeliveredDensity
ii. Actual DeliveredDensity
iii. Firecontrol
iv. Fire suppression