1. ISO Recommendation R-1999. Assessment of Occupational Noise Exposure for Hearing Conversation Purpose, International Standards Organizatio, Geneva, Switzerland: 1971.
2. Department of Employment. Code of Practice for Reducing the Exposure of Employed Persons to Noise, Her Majesty’s Stationary Office, London, UK: 1972.
3. Arrete royal etendant la surveillance medicale des travailleurs confiee aux services medicaux du travail et modifant les tires II et V du reglement general pour la protection du travail, 10 April, 1972, Arrete royal relatif a la lutte contre les nuisance, Belgium, 23 May 1974.
4. The Working Environment Act, Law No. 681. Denmark, 1975.
5. Journal Official de la Republique Francaise (1969), Decert No. 69-348, 12 April 1971.