In reply to Maximusf:
Ta, I'd seen the photos this afternoon but didn't respond as I needed to go and pick my girlfriend up from the station.
These helmets have a 3 part construction, Expanded Polypropylene (EPP) on the sides, Expanded Polystyrene (EPS) over the crown and a thin section of formed ABS (some long chemical name I don't know off the top of my head) over the the EPS. The idea being that the ABS protects the EPS section from minor impacts and surface damage such as standing up under a roof and smacking your head on the crag, in a big hit the ABS will spread out the load over a wider area of the EPS reducing the stress applied to the EPS and enabling a greater volume of the material to be involved in absorbing the energy of the impact. The EPP on the sides is a bit better at dealing with being shoved in bags etc as it can flex and return to its original shape.
EPP absorbs energy elastically (think what happens when you put a rubber under pressure) and can often take multiple impacts while EPS absorbs it by breaking apart (the stuff used in climbing helmets and bike helmets works on the same principle as polystyrene, just able to absorb more energy and being less prone to lose bits).
A mate took a massive lob off Kelly's Overhang a few years ago and wrote off a BD helmet, they gave him a hefty (circa 50% I think?) discount on a replacement which he gladly accepted on the rationale that he walked away from the accident without brain damage so the helmet did its job (I had a similar mentality to replacing a bike helmet a few years ago). Video for context of how bad the head impact was (Not Safe for Life Warning):
https://www.google.com/search?q=kelly%27s+overhang+weekend+whipper&rlz=...
Given the divot taken out of the side of yours any load applied to that area will be distributed over a smaller volume, a similar impact in the same position would have a higher likelihood of cracking the helmet on that section so I'd definitely not be trying to repair the helmet (the crash replacement stuff that manufacturers do is typically to discourage people using helmets that are damaged or have been bodge repaired). This response is of course relatively conservative given that I haven't got it in hand to look at in detail, my old Petzl Scirocco (the entirely EPP one, not the mixed EPP and EPS versions sold now, unfortunately out of use due to being stolen) had several dings in the crown section from me smacking my head, but I was confident it was safe to use still as they were relatively small.
I'll try and take a more detailed look at the photos on Sunday in terms of what I am trying to show in the equipment maintenance document.
@Dunthemall Thanks for pointing Max at my thread