Employees must be protected against noise whenever sound levels, read with a standard sound level meter set to A-weighting and slow response, exceed the permissible exposures in Table D-2: 90 dBA for 8 hours per day, 92 for 6, 95 for 4, 97 for 3, 100 for 2, 102 for 1 1/2, 105 for 1, 110 for 1/2, and 115 dBA for 1/4 hour or less. When exposure exceeds the table, the employer first applies feasible administrative or engineering controls. If these do not bring levels within the table, personal protective equipment meeting subpart E is provided and used to bring exposure within the table. Noise with maxima recurring no more than 1 second apart is treated as continuous. Wherever sound levels exceed the table values, a continuing, effective hearing conservation program must be administered. Where a day includes periods at different levels, the combined effect is evaluated using the dose fraction Fe, the sum of each T divided by its L, with T the actual time at a level and L the permitted duration at that level; a sum above 1 means the permissible exposure is exceeded. The text works an example of 1/4 hour at 110 dBA, 1/2 hour at 100 dBA and 1 1/2 hours at 90 dBA, which gives Fe of about 0.94 and so stays within the limit. The text advises (using should) that peak sound pressure from impulsive or impact noise stay at or below 140 dB.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.