Occupational exposure limits for a material or hazard expressed as an 8 hour time weighted average value (TWA) that includes the whole of the shift exposure. For noise it is a single number equivalent value in decibels that represents the equivalent average level of the actual changing noise levels.

When the exchange rate is chosen as 3 dB the average noise level is called the Leq. When the exchange rate is chosen as 4 dB the average noise level is called the LDoD. When the exchange rate is chosen as 5 dB the average noise level is called the LOSHA. In the example above the blue line shows the minute by minute changing noise levels from 65 to 92 dB while the horizontal black line shows the equivalent TWA value at 80.9 dB.