Looking at this further, if you set _fadeFire to true when the crash site is spawned it should dwindle with time.
// [_guaranteedLoot, _randomizedLoot, _frequency, _variance, _spawnChance, _spawnMarker, _spawnRadius, _spawnFire, _fadeFire, _prewaypoints, _damage]
nul = [3, 4, 400, 0, 0.99...