These light weight helmets, like the Altios and Elios, are one shot helmets. Petzl outlines several "retirement" scenarios on their website, but essentially, check your helmet after any impact. If there is any obvious damage or the impact was very significant, retire the helmet. I've had an Elios for 4 years and taken several good wallops from falling ice while ice climbing. The helmet took the blows like a champ and I don't hesitate to keep using it. If I ever took a substantial hit, or if the helmet reaches 10 years old, I will retire the helmet. These helmets aren't like the heavy artillery helmets that people used to climb in... they're more like bike helmets... one "significant" hit and they should be retired... no one wants to define "significant" because no one wants to be liable to an exact definition of when to retire equipment.