oneten wrote:Moreover, saying that without a helmet a rider would just suffer some surface some bruising and surface laceration seems as subjective and unscientific a prediction as saying that it saved a cyclist from a more severe head injury.
Not really, the OP described a classic failure mode of a helmet, with no suggestion of anything other than failure. Brittle failure of expanded polystyrene foam absorbs virtually no energy.
To absorb energy (which is how we prevent serious injuries) the EPF needs to compress - this is either plastic (leaving a compressed helmet shell) or it is elastic (returning to the previous thickness) which is very limited, it plays a very small role.
If I said that my seatbelt snapped and therefore saved my life in a minor crash you'd suggest that the seatbelt had failed, rather than doing any good...
I didn't even mention that the extra size and weight of the helmet may have contributed to the impact, nor that the very act of wearing the helmet may have influenced the approach speed and caused the fall in the first place.