I had a friend who, years ago, had about 40-50,000 rounds of ammo in his basement. A nosey and ticked off neighbor 'reported it' to (we think) the Fire Marshal...

Emergency Flare Storage and Handling Procedures

Flares are a safe and stable item to store.

D.O.T. classifies flares as a flammable solid but they are not particularly sensitive to initiation. There is no threat of mass explosion. There is no threat of an individual flare exploding.

Flares should be stored in a cool, dry place away from excessive heat (above 167 degrees F), sparks or flames

While flares have no expiration date when properly stored, storage above 120 degrees F for long period of time (over 1 week) should be avoided. Normal recommended storage temperatures are 40 degrees to 90 degrees F.

To preserve the reliability and excellent performance characteristics of flares, do not expose the units to water for periods longer than 10 minutes - flares should be stored under dry conditions.