Why close isolation valve and APU bleed air for engine fire?

[Billcoke 3]

For engine fire, the reason to close the packs (affected side) is to prevent smoke from filling up the cabin? But why the Isolation Valve and APU Bleed Air need to be closed too?

[Chock 17,758]

I presume it is following the basics of fire prevention theory, in that if you starve a fire of any of the three things necessary for a combustion (heat, fuel, oxygen), it will go out. Since those systems are pushing air around the plumbing of the airliner, shutting them off has the potential to stop feeding one of the big three of the combustion triangle to a fire somewhere in the system. The action won't necessarily stop a fire, but it may possibly assist in slowing it down somewhat.

[Billcoke 3]

54 minutes ago, Chock said:

I presume it is following the basics of fire prevention theory, in that if you starve a fire of any of the three things necessary for a combustion (heat, fuel, oxygen), it will go out. Since those systems are pushing air around the plumbing of the airliner, shutting them off has the potential to stop feeding one of the big three of the combustion triangle to a fire somewhere in the system. The action won't necessarily stop a fire, but it may possibly assist in slowing it down somewhat.

Now I get it. Many thanks....

[Billcoke 3]

5 hours ago, Chock said:

I presume it is following the basics of fire prevention theory, in that if you starve a fire of any of the three things necessary for a combustion (heat, fuel, oxygen), it will go out. Since those systems are pushing air around the plumbing of the airliner, shutting them off has the potential to stop feeding one of the big three of the combustion triangle to a fire somewhere in the system. The action won't necessarily stop a fire, but it may possibly assist in slowing it down somewhat.

But wouldn't that shuts the cabin air-conditional too? Or as long as the unaffected packs (ie. the right side) is still left open, there will be air inside the cabin.

[Chock 17,758]

1 hour ago, Billcoke said:

But wouldn't that shuts the cabin air-conditional too?

hmmm, tricky choice, turn off the air conditioning and have people be a bit stuffy during the two minutes they are evacuating, or leave it on and allow the aeroplane to become a blazing death trap.

Edited July 26, 2020 by Chock

[HighBypass 2,337]

The pack from the other intact engine will ensure that your pax can scream in comfort.. 

[Billcoke 3]

9 hours ago, HighBypass said:

The pack from the other intact engine will ensure that your pax can scream in comfort.. 

hahaha......