@ TamdemJeremy
I was present when Simwit had his tumble and I don't need to read any websites, test results or tea leaves to realise that the helmet saved him from a head injury. As you say the helmet has "failed" because it has split but the helmet has nevertheless prevented a head injury and that has to be a good thing.
The ground where the incident occurred had exposed rocks on it and one/some of those rocks impacted with Simwit's helmet. The helmet received the impact from the rocks and this helmet has the marks to prove this (although the photo's don't show this too clearly). If he had not been wearing the helmet the rocky ground would have impacted directly with his skull and caused injury.
As Simwit says – Wear your helmet kids.