B777 cargo bay pressures?
 

i was thinking about how the reduced pressure in the cargo bay might affect a box full of lithium battery cells. What would be a typical or lowest exected pressure (e.g. highest altimeter pressure)?

There is no reduced pressure the cargo bays are within the pressure hull.

I you were to take off at sea level, you still suffer a pressure drop as with the rest of the cabin to 8000 cabin alt. About a 4psi drop in absolute pressure.

Swelling of lithium cells in cargo bay
 

A -4 psi delta pressure on a cell could cause the casing (metal or plastic) to bulge outward and deform the internal current collectors and create an internal short circuit. A shorted cell could vent or burst and produce noxious fumes and/or fire depending upon the chemistry and size, energy content, etc.

Now i have to question whether MH370 did indeed carry lithium cells in the cargo bay, or if that is just a rumor?

I haven't read the MH thread, far too much there, anyway aren't lithium cells CAO freight these days?

My reply was such that the OP thought the cargo bays were unpressurised.

lithium ion batteries
 

I would have thought so!
Lithium ion batteries if a burr or scraping or filing comes in contact with other parts inside the battery a short circuit occurs the temperature could reach 500 degrees Celsius thermal runaway This could cause a fire if not packaged properly so yes I would say (Dangerous Goods)

B777 Cargo Bays
 

Very much pressurised!
As previously mentioned, similar pressure as the cabin

I'm missing something here, What is OP in this phrase???

TW

i guess the battery rumor was true
 

Evidently 5400 lbs of lithium batteries were in the cargo bay of MH370.

Is there any path for fumes or vapors from the cargo bay back into the passenger compartment?

i was thinking that this would not be likely, but could it happen? In a simplified path, the fresh air is compressed and pulled from in front of the engine, then conditioned and routed thru the passenger area, then down thru avionics and then thru the cargo hold and excess pressure bled off out the rear of the fuselage.

My theory is that the -4 psi pressure difference caused some internal shorting that caused some cells to pressurize and vent noxious fumes into the air (e.g. CO ), and any recirculation might have put everyone to sleep permanently. Then they flew on autopilot till the fuel was gone. Seems to fit the situation with no conspiracy or rogue pilots required...

OP is the original poster of a thread.

Kenneth House thanks for the OP answer.....

TW

Lots of people fly with devices containing Lithium Ion batteries day in day out. The change in cabin pressure doesn't cause them to bulge and spontaneously combust.

I'm not sure why you theorise that they would do so in the cargo hold?

Also, did MH370 actually carry a couple of tonnes of lithium ion batteries or was it a consignment of devices containing lithium ion devices? I haven't kept up with the story much lately.

If it was the former I'd be very surprised they were allowed as freight on a passenger flight.

Not sure of the policy at Malaysian but where I work we can carry lithium ion batteries as cargo in passenger aircraft. We can not carry lithium metal batteries on passenger aircraft unless they are contained in equipment.