This part of the standard specifies requirements for construction, design, performance, marking and user information for ear-muffs fitted to an industrial helmet which complies with EN 397. In particular, it specifies the sound attenuation of the helmet mounted ear-muffs, measured in accordance with EN 24869-1. Because one model of ear-muffs designed to be attached to an industrial safety helmet can be fitted to a number of helmet models and sizes, this part of the standard sets out a series of physical and acoustic requirements for the ear-muffs when fitted to the specified model(s) or size(s) of helmet. All requirements apply to the ear-muffs fitted to one of the specified models or sizes of helmet (the basic combination), and an abbreviated set of requirements apply to the same model of ear-muffs when fitted to the other specified models or sizes of helmet (the supplementary combinations). Information on the range models of helmet tested with the ear-muffs, and for which the combination satisfied this standard, is required to be made available. Ergonomic aspects are addressed by taking into account, within the requirements, the interaction between the wearer, the device and where possible the working environment in which the device is likely to be used (see Annex ZA and EN 458).