Here is a cut and paste post from another forum I frequent, just saw this, sounds plausible…NOx has an orange color…
"Who knows what caused either fire, but powder as it ages will auto ignite. The general public is totally unware of this, but the military has had lots of auto ignition events.
You won’t find out about the US events, an Insensitive Munitions expert I know, we conducted a Google search on one which he wrote the after action report. Nothing to be found on the web. These things just don’t make it out to the public.
World wide, there is an ammunition dump going off at least quartely, if not monthly.
This one went kaboom in the Congo this month. Big kaboom.
You really should use up double based powders by 20 years and single based by 45 years.
Section from the Propellant Management Guide:
Stabilizers are chemical ingredients added to propellant at time of manufacture to
decrease the rate of propellant degradation and reduce the probability of auto ignition during its expected useful life.
As nitrocellulose-based propellants decompose, they release nitrogen oxides. If the nitrogen oxides are left free to react in the propellant, they can react with the nitrate ester, causing further decomposition and additional release of nitrogen oxides. The reaction between the nitrate ester and the nitrogen oxides is exothermic (i.e., the reaction produces heat). Heat increases the rate of propellant decomposition. More importantly, the exothermic nature of the reaction creates a problem if sufficient heat is generated to initiate combustion. Chemical additives, referred to as stabilizers, are added to propellant formulations to react with free nitrogen oxides to prevent their attack on the nitrate esters in the propellant. The stabilizers are scavengers that act rather like sponges, and once they become “saturated” they are no longer able to remove nitrogen oxides from the propellant. Self-heating of the propellant can occur unabated at the “saturation” point without the ameliorating effect of the stabilizer. Once begun, the self-heating may become sufficient to cause auto ignition. "