Cargo compartment (Class C) fire

[arff]

It is my understanding that, on the Airbus & Boeing aircrafts, cargo holds below the main cabin floor deck are being pressurized with air coming from the main cabin. If this is the case, it is possible that a fire in these cargo compartments may travel into the main cabin through that air duct. Does any one know if, once the cargo fire detection system has been activated, that air duct closes automatically ? Thanks.

[HZ123]

I would be very interested in the answer to this. As a trainer on ramp activities we have been told a number of times about the damage to 747 door seals causing leakage of air into the holds thus increasing the fire risk. I have also been told that cargo holds are pressurised but not to the same level as the pax cabin. This cannot always be the case as live animals are carried in the holds. L
ets hear from an expert. Thanks

[rwm]

All the passenger aircraft I have worked on, B727,737,F28, D8, F27, F100, SH360,Bae146,ect. The bagage compartments are covered in a fire retardent material similar to fiberglass. All the seams are covered in fire retartdent tape, and there is no real duct going to pressurize it specificaly. Picture the fusalage as a can, with a floor across half of it. Under this floor you put a box. Then you put in a tube to pressurize the top part of the can, and a valve to limit how much air stays inside. Everything in the can will be pressurized. Inside the box under the floor, (which is sealed,(not totaly air tight))is a fire retardant system consisting of a detector and a extinguishing agent. So if you get a fire in the box, some smoke may come out, but the extinguisher puts it out, and you may then get a bit of smell from the extinguisher. This is a symplified way of how bagage hold are in passenger a/c.