Fire Science

Question 1

What is Pyrolysis?

Answer 1

The thermal decomposition of a substance by heat.
When exposed to enough heat, a substance breaks down and begins to give off flammable gases.

Question 2

What is a passive agent?

Answer 2

Something that absorbs heat from a fire

Question 3

What is the lower explosive limit?

Answer 3

The lowest concentration of fuel that will support a self propagating flame

Question 4

What is the Upper explosive limit?

Answer 4

The highest concentration of fuel that will support a self propagating flame

Question 5

What are the 4 phases of a fire

Answer 5

1 Early phase
2 Growth Phase
3 Fully Developed Phase
4 Decay Phase

Question 6

What is the effect of a Short pulse

Answer 6

Dilutes flammable gases stopping them reaching their auto-ignition temperature

Question 7

Define a Backdraft

Answer 7

Limited ventilation in a compartment fire leads to a high concentration of unburned pyrolysis products.
The Admission of air when an opening is made can lead to a sudden deflagration.
The deflagration moving through the compartment and out of the opening is known as a backdraft and has the potential to damage the building.

Question 8

What are the Signs and Symptoms of a Backdraft? (8)

Answer 8

Fire with limited/No ventilation.
Hot doors and windows
Pulsating smoke through small gaps and openings.
Soot blackened windows
Smoke being drawn back into openings (Possible whistling)
Ghosting tongues of flame
lack of visible flame
Change in fire conditions, fast moving smoke, steadily darkening in colour.

Question 9

Define a Flashover

Answer 9

The sudden and sustained transition from a growing fire to a fully developed fire.

The total thermal radiation from the fire flume, hot gases and hot compartment boundaries, causes all exposed combustible surfaces to pyrolyze and ignite where there is adequate ventilation.

Question 10

Signs and Symptoms of a flashover (7)

Answer 10

Well Ventilated, free burning fire

High heat conditions

Flaming combustion- ghost flames overhead

Sudden lowering of the smoke layer

Rapid rise in temperatures

Low level materials starting to pyrolyze.

Change in fire conditions, fast moving smoke, steadily darkening in colour.

Question 11

Define Fire Gas Ignition

Answer 11

When gases from a compartment fire have leaked into an adjacent compartment, and mixed with the air.
This mixture may fall within the flammable limits, that, if ignited will create an increase in pressure either with or without explosive force.