AS NZS 1269.4:2014 Occupational noise management
9.5 Updating of reference audiograms
The reference audiogram shall be updated whenever a significant threshold shift has occurred or every 10 years, whichever occurs sooner. After a significant permanent threshold shift has been found and medically assessed, the employer shall ensure that an updated reference audiogram is obtained for the test subject. Subsequent monitoring audiograms shall then be compared with this most recent reference audiogram. Records of previous reference audiograms shall be retained.
9.6 Audiometric data base analysis
Assessment of the audiograms of individual test subjects may be supplemented, where practicable, by audiometric data base analysis. Audiometric data base analysis evaluates trends in the audiograms of test subjects as a group and may detect signs of occupational hearing loss in a group of test subjects before large threshold shifts occur for individuals. It may therefore provide early warning of shortcomings in a noise management program and enable early corrective action to be taken.
NOTE: This is more applicable to large organizations as opposed to small to medium sized organizations.
10 EVOKED OTOACOUSTIC EMISSIONS
Evoked otoacoustic emissions (EOAE) are an indicative measurement of the damage to the outer hair cells of the inner ear (cochlea) caused by ageing, disease, noise or ototoxic agents. They are a fast objective measurement and useful tool and may offer early detection of sub-clinical damage to the hearing mechanism.
NOTE: There is currently no recognized or internationally agreed measurement procedure applicable for EOAEs. Work at an international level is currently being co-ordinated by the UK HSE to standardize an EOAE measurement procedure applicable in workplaces. See: Health and Safety Executive (2011), Report of an International Expert Symposium on the usefulness of Otoacoustic Emissions (OAE) Testing in Occupational Health Surveillance 8-9 th February 2011. www.hse.gov.uk/noise/OAE-expert-symposium-paper-jan-2012.pdf
NOTE: The estimated prevalence and degree of noise-induced hearing loss and percentage loss of hearing in noise-exposed populations are given in Appendix F. Appendix F provides information that may be used by organizations to set noise exposure criteria lower than those given in legislation.