Hearing protectors are chosen and looked after under AS/NZS 1269.3 (hearing protector programmes), with workers involved in the choice and offered a reasonable range of types. Suppliers should supply the full attenuation picture, including the SLC80 rating, the class and the octave band figures, measured under AS/NZS 1270. The PCBU weighs how much attenuation the environment needs, using Table 4 (class 1 for an LAeq,8h under 90 dB(A), class 2 from 90 to under 95, class 3 from 95 to under 100, class 4 from 100 to under 105, class 5 from 105 to under 110) while steering clear of over-protection that blocks spoken instructions and other sounds needed for safety; whether the type suits the environment and the task, since earplugs are hard to keep hygienic when inserted with dirty hands whereas ear-muffs are uncomfortable in the heat and awkward in tight spaces or with a helmet; and the comfort, weight and clamping force of the device. Fit decides how much protection a person actually gets: fitting aids exist, other gear such as hard hats, dust masks and eye protection can spoil the seal so fit is checked with that gear on, and anyone who wears spectacles is fitted wearing them.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.