To answer your question, I Googled the question – “Are aircraft cargo holds pressurized? “, and got several answers, about temperature and pressure conditions in cargo. There are two cargo holds - one part right behind the crew cabin, may indeed be made liveable, for pets, and live (lobsters) restaurant food shipments. The “aft cargo” hold isn’t likely to be – no need for the extra T & P conditioning load for “dead-weight” items. Meanwhile, sometimes “stowaways” survive such high altitude conditions when they stuff themselves into aircraft wheel wells.
As for the “loosely capped” ASG-33 lube grease tubes, I wouldn’t want to risk travelling on a plane, not knowing if a dealer shipped this (Amazon purchase) product in the aft cargo, and whether the high altitude pressure drop causes outgassing and pops the lube cap. There probably are cargo fire extinguishers in there, if it should ignite. (Somewhat, kidding ?)
Anyway, such products being shipped must surely require a signature, declaring that they are not hazardous, but then it is a matter of the shipper’s opinion.
I’ve probably exhausted the case for lube shipping concerns here and I am confident AP takes the appropriate common sense measures and precautions, to safely ship its special lube, where possible. So perhaps, we shouldn’t expect the lube product to be made generally available everywhere. Wonder if even the CONUS postal services or truck transports, have any special concerns or restrictions, handling such materials.
As for where potentially combustible petro-chemicals might be “unknowingly” stowed, as cargo or luggage - Hard to predict, but surely hazardous or out-gassing products wouldn’t share the same pressured and temperature controlled, animals (liveable) forward cargo area. Here below, are two of the search results:
F.Y.I. – Joe
are aircraft cargo holds pressurized?
The round shape of the fuselage outline is very efficient at withstanding pressure. Because of that, everything within the fuselage shape is pressurized. This includes the cargo hold below.
Only cargo holds located behind the aft pressure bulkhead would be unpressurized, and these are mainly found in smaller aircraft.Aug 21, 2014
Are “luggage compartments” on planes pressurized?
Yes, they are both pressurized and temp controlled, because of some of the "live" cargo they carry (pets, live animals for restaurant menus). Also, some of the larger wide-body aircraft have galley facilities in the cargo hold area that flight attendants have to access during flight.