This document is intended as a guide to the selection of silencers which are appropriate for use with various noise sources. It is aimed at the practising engineer with a limited knowledge of acoustics to assist in the Specification of the most suitable silencer for a particular purpose and to assess its operation when it is installed. In addition it should assist him in reviewing differing proposals submitted by vendors. However@ the experienced acoustic engineer may also find it useful as an aide-memoire.The guide places considerable emphasis on the mechanical aspects of silencers which have to be considered for various applications so that due consideration can be given to engineering design@ operational aspects@ safety@ and cost.