This part of the Standard is concerned with ear-muffs whose passive acoustic performance may be augmented by a noise cancellation electronic circuit. It specifies constructional, design and performance requirements, methods of test, marking requirements and user information. This part of the Standard does not deal with ear-muffs for attachment to a helmet or which are part of a helmet. Neither does it deal with open-air electronic earphones that are not intended to provide attenuation. The requirements of this standard are intended to take account of the ergonomic interaction between the wearer, the device and where possible the working environment in which the device is likely to be used (see Annex ZA, of this standard and EN 458).