Structural weight & complexity to accommodate jettison system?

Additional systems to execute the jettison?

CG change? To minimize this you would need multiple selective jettison bays...$$$$

You could really only jettison over water or perhaps severely uninhabited areas. FAA would not approve otherwise.

Depressurization?

Not the answer, by a long shot.

Depressurization is the answer for certain classes of compartments and some fires.

Bring the cabin to 25,000' works, in some cases. Last ditch for sure.

GF

I meant jettisoning cargo is not the answer. Depressurization would have to be part of that. That might put the fire out but then you have to decide whether to stay high to keep the fire suppressed or descend to land. If you're over water, might as well stay high I guess at least until your O2 runs out.

Might not save you from a box of lithium batteries.

Why not start by just actually putting robust main deck fire suppression systems on board?

Jettison issues aside, the problem with main deck suppression isn't an easy one. The main issue is that the crew effectively inhabits the "main deck" along with the cargo. There is no way to seal off the main deck. On the 777F, we can even have a cockpit door due to depressurization airflow/air-load issues on the aircraft structure during a rapid-D. Trying to seal the main deck cargo compartment to allow a suppression agent to be effective (like the lower class-E compartments) isn't feasible.

Fedex has installed an after market main deck FSS. It uses an array of sensors for the main deck positions and a bayonet system which pierces the metal cans and injects an argon based foam or in the case of a pallet, lays down the foam on the pallet. Certainly better the the basic aircraft option (depressurization and main deck airflow control). There was at least one false alarm that didn't pierce the can because the can roof was defective and not rigid enough for the bayonet to puncture. It's also ineffective against a sustained LI battery fire as are all currently available FS agents.

Back to the depressurization thing for a sec. The best option for fighting an in-flight fire is landing withing 15 minutes. The Boeing depressurization for a main deck smoke warning is only going to be used if you're ONLY option is to spend time at altitude due to the proximity of available airports. That portion of the checklist is going to be skipped right over if the aircraft is anywhere over the continental US or anywhere else with easy access to concrete. The other time I'll skip that option is if I know we've got a sustained LI battery involved fire and I'm not within 15-20 min of a runway. Then it's an off airport landing in a remote area or controlled ditch.

Or this.

Engineer Designs Cabin That Can Detach Itself From An Aircraft In An Emergency | IFLScience

Take notice which part of the plane stays attached. FU commie engineer.

Gives the pax guys some options with a takeover attempt or maybe just an unruly bunch in the back.

"Ladies and Gentleman, this is your Captain. You have two choices. Kill or if possible restrain the idiots threatening the cockpit and let me know when you're done or I'm going to jettison the whole lot of you. That is all."

"The cabin’s design also includes storage space, so cargo and passenger luggage as remains safe, The Independent reports."

Thank heaven the luggage is safe!

Give me one reason why lithium batteries can't exclusively be transported by truck, rail or boat.