1.1 ,This specification covers performance requirements for helmets used by downhill mountain bicycle riders. Studies have shown higher risk to the head and face for this sport as compared to recreational street riding, hence, this specification requires greater impact protection and provides performance criteria for chin bars on full-face helmets, but does not require full-face helmets. This specification recognizes the desirability of lightweight construction and ventilation, however, it is a performance specification and is not intended to restrict design.