RFT 002: Fire Science 2

Question 1

What are the two main types of flame?

Answer 1

Diffused
Slow and bright, flickers to seek oxygen, unclean burn, orange/red

Premix
Hotter, clean burn, gases are mixed prior to ignition, blue flame

Question 2

What does LEL and UEL stand for, and what are their definitions?

Answer 2

Lower explosive limit
The lowest concerntration of a fuel that will support a self-propagating flame

Upper explosive limit
The highest concerntration of a fuel that will support a self-propagating flame

Question 3

What are the four phases of fire development?

Answer 3

Phase One
Developing
Fire develops at a slow rate, but the rate increases with time due to passives reaching their thermal load and reflecting heat back into the room

Phase Two
Flashover
Sharp rise in temperature causing pyrolysis

Phase Three
Fully developed
Fuel or oxygen in the compartment will affect how long the compartment and all its contents will burn

Phase Four
Decay
The fire will gradually die back as fuel or oxygen is consumed

Question 4

What does thermal load mean?

Answer 4

When passives reach their thermal load, it means they can no longer absorb heat from the fire, so they release heat back into the room, causing a rapid increase in temperature

Question 5

What are the two areas of pressure called in a fire compartment, and what divides them?

Answer 5

Overpressure - pressurised above atmospheric pressure
Under pressure - slightly below atmospheric pressure
The neutral plane is the visible border between the two

Question 6

What is the 4-2-1 rule of thumb?

Answer 6

A flashover occurs rapidly in a fire in the corner of a room (4), twice as quickly as against one wall (2), and four times quicker than a fire in the middle of the compartment (1)

Question 7

What are the three main fire hazards that’s firefighters might occur during a fire?

Answer 7

Flashover
Backdraught
Fire gas ignition

Question 8

What is a flashover?

Answer 8

A sudden and sustained transition of a ground fire into a fully developed fire
A fire in a room to a room on fire

Question 9

What temperatures can be reached in the overpressure?

Answer 9

700-1000°C

Question 10

What are the signs of a flashover?

Seven answers

Answer 10

A ventilated fire with an adequate oxygen supply
Flames visible in the fire gases at ceiling level
High temperatures and an increasing rate of combustion
Neutral plane moving down
Sudden increase in fire development
Pyrolysis at floor level in the compartment
Increased turbulence of the neutral plane

Question 11

If the signs of a flashover are identified, what actions should be considered?
Six answers

Answer 11

Withdrawing and firefighting from outside the compartment
Communicate the hazard to other firefighters, the ECO, sector commander or IC
Ventilate to remove gases, only with IC permission
Use the thermal image camera to assess temperatures
Teams should stay low in cooler air
Pulse spray into the overpressure to cool gases and reduce radiated heat

Question 12

What is the definition of a backdraught?

Answer 12

A deflagration caused by air being introduced to a fire compartment that is oxygen starved

Question 13

What is the definition of deflagration?

Answer 13

An intense fire which moves rapidly outwards in all directions through flammable gas

Question 14

What are the external signs of a backdraught?

Five answers

Answer 14

Fire with limited or no ventilation
Fire has been burning for some time
Fire gases being pushed out under pressure from gaps
Windows blackened with no visible signs of flame
Fire gases pulsing out from gaps

Question 15

What are the internal signs of a backdraught?

Five answers

Answer 15

Low neutral plane
Darkening of fire gases
Inrush of air and fire gases forced out through the opening
Pulsation of gases through an opening
Deflagration through an opening

Question 16

If the signs of a backdraught are identified, what actions should be considered?
Five answers

Answer 16

Communicate the hazard with other firefighters, the ECO, sector commander or IC
Consider ventilating the compartment prior to entry
Use the TIC to assess temperatures
Always use correct door procedure when making an opening
Pulse spray the interior to cool and dilute the fire gases

Question 17

What is fire gas ignition?

Answer 17

A sudden deflagration or explosion caused by the ignition of fire gases accumulated outside the fire compartment

Question 18

What are the signs of fire gas ignition?

Two answers

Answer 18

Fire has been burning for some time

Accumulation of fire gases outside the fire compartment

Question 19

If the signs of fire gas ignition are identified, what actions should be considered?
Four answers

Answer 19

Communicate the hazard to other firefighters, the ECO, sector commander or IC
Consider withdrawing from the building
Ventilate the fire gases from the adjacent compartments
Cool and dilute fire gases that leaked from the fire compartment

Question 20

What happens to gases when pulsing takes place within a compartment?

Answer 20

The oxygen exhausts, flames go down
Temperature drops, lowering the pressure
This draws air into the compartment through any gaps
This allows burning to take place, increasing temperature
Pressure increases preventing further air from entering