On Tue, 24 May 2016, Peter Fairbrother wrote:
You'd need major structural failure with LACK of immediate ignition,
followed by release of the propellants into some sort of containment (a
big pit for the rocket to fall back into?) so they mix in bulk rather
than boil away furiously and disperse...
Boiling away might be a very bad thing - the cold mixed vapours would have quite a large density, and also a very large external surface area - so coupling with the atmosphere would be much greater...