Text frågor, suprise test 7/10

Question 1

What is fire?

Answer 1

Fire is the visible effect of the process of combustion. It occurs between oxygen in the air and some sort of fuel. The reaction from the chemical reaction is completely different from the starting material. Exothermic reaction that leaves heat, light and combustion products.

Question 2

How can a candle burn?

Answer 2

1. The light ignites and waxy coating over it melts
2. Wax melts turn into gas and diffuses out to find O2
3. Gases oxidate and burn. Flame occurs
4. The flame radiates heat downward to melt solid wax
5. Molten wax moves up and the wick and the process continue. (buoyancy)

Question 3

What is a flashover and around what temperature does it happend?

Answer 3

Flashover is a thermally driven event during which every combustible surface exposed to thermal radiation in a compartment or enclosed space rapidly and simultaneously ignites. It occurs around 500-600 degrees celcius

Question 4

What is backdraft? How can firefighters avoid injury from backdraft?

Answer 4

When the fire is oxygen-dependent and pyrolysis starts. When oxygen comes in and can help the fire to start again, then you have a backdraft.
firefighters can open up the roof to let the fire cool down.

Question 5

In a room fire, the temperature of the gases resulting from the fire is 200 degrees. What would be their corresponding density?

Answer 5

Density= 353/T(in Kelvin)

Question 6

Why do ethanol and methanol have a combustion efficiency of 1? What happends to their diameter dependence?

Answer 6

Complete combustion, no smoke particles will be made.

Question 7

Which plume equation set has a condition relation to the mean flame height?

Answer 7

Hesskestad Plume equation
z0= 0.0083Q^(2/5) -1.02D

Question 8

What is a neutral plane in a room fire indicate its position in the following figures. (se papper)

Answer 8

Neutral plane marks the level in a structure fire where below it air be drawn into the structure and above it combustion gases will be exhausted.
Altenativt:
Neutral plane: where smake/hot gases. (Higher pressure) are exhausting out of the top of the vent opening and it is drawing a current of cooler/freash air (lower pressure) in through the bottom of the opening.

Question 9

What is the difference between enclosure surface area, AT, and total enclosure surface area, At?
And what is A0?

Answer 9

AT= the total area of the room - the openings
At= the total area of the room
A0= Area of the opening(s)