The most dangerous thing for storing ammunition is the age of the ammo, how it was loaded (reloaded), and what the humidity in storage is.
I keep a dehumidifier running 24 hours a day in my basement, and I don’t even reload. I also keep my ammo in fireproof file safes and inspect regularly for corrosion, etc.....
I have about 500 left of 600 rounds of WCC 42 45 ACP ball ammo that is circa US 1942 that I’ve been watching...recently went to the range and shot 100 rounds flawlessly (only trouble is the propellant is corrosive and the gun needs to be cleaned very well afterwards....)
An alternate method is to store your ammo in zip-lock bags, in a surplus steel ammo can with good rubber seals. If you store your ammo away in winter when in-house humidity is low, then it should keep for a while.
There are three separate issues in your statement.
From what I have read, age produces little degradation if the ammunition is stored in a cool, dry place.
How the ammunition was reloaded can be critical for how safe the ammunition is, but that is the safety of the ammunition, which is a related by separate issue, IMHO.
Humidity is very important, but it does not make the ammunition more dangerous, just less reliable.
Heat, humidity, and petroleum products seem to be the biggest enemies of ammuniton for long term storage.
I do not recall anything about long term storage of conventional ammunition that would make it subject to detonation.
This is common with the storage of dynamite, where the nitroglycerin in the dynamite slowly separates form the filler and creates an incredibly dangerous situation. The nitroglycerin can be set off very easily by friction or shock.
IMHO, small arms ammunition is far less dangerous to store than gasoline or propane.