I forget my exact results but for the last two years I have conducted a
firing of many expired flares on New Years eve. Of the 12 guage
flares, ALL fired, even those 12 yrs out of date. However, most of the
out of date ones either failed to ignite or otherwise sputtered.
The Olin (now Orion) hand held flares were worse than useless and ALL
failed to light, even the current ones. All of the Pains-Wessex hand
held flares ignited and worked very well, even some 5 yrs out of date.
The single Pains-Wessex parachute flare that was 9 years out of date
fired but the parachute failed.
The tiny pen-like "Skyblazer" flares all worked very well far outdoing
the 12 guage flares, too bad they seem to be off the market.
You'd be lucky to get those old Olin hand flares to ignite by pouring
diesel on them.