The employer must review, and revise if needed, its noise controls: before changing plant or a system of work in a way likely to push exposure over the standard; when an audiological report under regulation 38 says an employee has probably suffered noise-induced hearing loss; after a Part 5 incident involving exposure above the standard; when controls fail to keep exposure at or below the standard; and when the HSR asks. The HSR may ask on reasonable belief that a trigger exists or that a review was not done properly or ignored a trigger.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.