In reply to Robin Ashcroft:
I would say the type of helmet you use would depend on what you think the biggest risk is, you taking a tumble or rocks falling from above. Climbing helmets are basically designed to protect you from rockfall from above (I think) so won't neccessarily protect you if you take a tumble, which a ski helmet will. I have first hand experience of this as I got hit on the forehead whilst falling in a climbing helmet and the helmet stayed in tact but my head was fractured. However, on another occasion when being directly underneath a rockfall in a climbing helmet, my helmet/head were fine.