This part of the Standard is concerned with ear-muffs whose acoustic performance may be regarded as being level-dependent, including those fitted with electronic sound restoration circuits and/ or noise cancellation systems. 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-ear 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).