The assessment depends on the type of workplace, the number of people potentially at risk and the information already held. It should be done during a typical shift and determine the noise levels produced during the various tasks and how long workers are exposed during each, taking account of physical and psychosocial risks: the plant, equipment and other sources in operation, how work is done, the length of the shift (long shifts raise exposure and job demands), and environmental factors such as walls, surfaces and workstation layout; consultation with workers and supervisors is essential to establish tasks and their frequency. Measurements should be taken 10 to 20 centimetres from the entrance of the worker's ear canal over a representative period, usually with a hand-held integrating sound level meter, or with personal sound exposure meters (dosimeters) where workers are highly mobile or access is difficult or unsafe. Measurements should capture the combined level of all tools, machines and processes plus background plant noise such as ventilation, compressors and pumps, and each source or activity separately to find the main contributors; the Appendix D ready reckoner combines levels and durations into a total LAeq,8h. One representative assessment suffices for a group with identical sources and likely exposure. For shifts of 10 hours or more the AS/NZS 1269.1 extended-shift adjustment is added to the measured LAeq,8h before comparison with 85 dB(A): +1 dB for 10 to under 14 hours, +2 for 14 to under 20, +3 for 20 or more; for work on more than five days a week the weekly averaging procedure in AS/NZS 1269.1 is used. The psychosocial risk from noise also depends on duration, frequency and severity of exposure.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.