DozyWannabe,
I know they did. My comment was rather tongue-in-cheek to all those saying "how could they do this? Didn't they think of the consequences?"
The development and physical properties of Li-Ion batteriy fires can be estimated quite well. Although maybe they were too optimistic on the likelihood, the mitigating measures may be adequate for the severity.
The probability of failure of the mitigating measure (venting override) of course has to fit the probability the of the original hazard (battery fire), and a redesign may be required in this case.
Bernd