Compressed Natural Gas (CNG / Methane, UN 1971) behaves differently from LPG during an accidental atmospheric release primarily because:

1. Methane has a vapor density of approximately 0.55 relative to air, making it lighter than air, so it disperses rapidly upwards into the atmosphere in open environments
2. Methane is non-combustible and cannot be ignited even in pure oxygen
3. Methane instantly freezes into solid dry ice blocks upon contact with oxygen
4. Methane emits intense red phosphorescence visible for 5 kilometers