Safety Critical Workers are commonly required to hear speech conveying safety critical information, in noise (a cab, shunting yard or worksite with background noise of 60 dB or more) or in quiet (a control room), and the operator determines which applies to each task and tells the health professional; the Standard assumes the closed-loop communication protocols of the RISSB Safety Critical Communications code and guideline. This hearing standard is distinct from the audiometric monitoring required for workers who use hearing protectors against noise above the exposure standard, although the operator and health professional manage the interface to optimise hearing conservation. Hearing loss is graded on the World Health Organization system by averaged thresholds and functional impact (Table 12), assessed by pure tone audiometry, with teleaudiology permitted in defined circumstances, and where indicated by speech discrimination in noise testing; hearing aids may be used to meet the criteria subject to periodic review of hearing and aid function. The fitness criteria in Table 13 set the thresholds and conditions for Category 1 and 2 workers by speech-in-noise or speech-in-quiet requirement, with Fit for Duty Subject to Review for those meeting them with aids or passing discrimination testing. Track workers whose hearing is needed only for their own safety meet the Category 3 criteria, and those wearing hearing protection against machinery noise cannot be expected to hear train horns and must work under the immediate supervision of a team leader who directs them to stop and clear the track.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.