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2. European Committee for Standardization (CEN). Hearing protectors—recommendations for selection, use, care and maintenance—guide document (Standard No. EN 458:2004). Brussels, Belgium: CEN; 2004.
3. European Committee for Standardization (CEN). Acoustics—hearing protectors—part 2: estimation of effective A-weighted sound pressure levels when hearing protectors are worn (Standard No. EN ISO 4869–2:1994). Brussels, Belgium: CEN; 1994.
4. International Organization for Standardization (ISO). Acoustics—hearing protectors—part 2: estimation of effective A-weighted sound pressure levels when hearing protectors are worn, technical corrigendum 1 (Standard No. ISO 48692:2006). Geneva, Switzerland: ISO; 2006.
5. Arezes PM. Risk perception in occupational noise exposure [doctoral dissertation]. Guimarães, Portugal: University of Minho; 2002. In Portuguese.