Noise Instrument Integrator Settings: What the Differences Show Us about Current Noise Exposure Standards
Sponsored by OHD, LLLP
Many modern noise measurement instruments are able to assess noise levels against a number of different occupational noise exposure standards such as OSHA, NIOSH/ACGIH, and the European Union’s Physical Agents (Noise) Directive. In the Americas alone, there are 16 different standards.
By providing a range of settings, these instruments can be used across a wide range of applications, giving an industrial hygienist a comprehensive set of data on which to build noise control measures or provide hearing protection.
However, providing a myriad of options introduces risk that the user chooses either the wrong setting before a measurement or the wrong parameter when reviewing the measurement data.
This can be a complex task, especially where a number of different standards are in force or where there is no clear definition of which standard should be used.
Noise measurement instrument settings include exchange rate, time weighting, frequency weighting, threshold level, criterion time, and criterion level. These settings are combined to create what is known as an integrator.
To illustrate the effect that different settings can have, consider a measurement made with a two-channel noise dosimeter. One channel was set to use settings consistent with OSHA’s Hearing Conservation Standard and the other with the EU’s Physical Agents (Noise) Directive settings. The measurement was made in a real-world situation and covered a period of 7 hours and 8 minutes. In basic terms, over the 7 hours and 8 minutes of the measurement, the noise exposure was reported as 75 percent of the OSHA HC limit and 511 percent of the EU limit.
Why are these two values so different? In this application, there are periods where the noise levels are below 80 dB. OSHA HC uses an 80 dB threshold, effectively removing noise below this level from the overall exposure. In addition, the use of the slow time weighting setting reduces the influence of impulsive noise sources (in this case a pyrotechnic cannon).
A further study (PDF) investigated the differences between the values reported by OSHA HC and NIOSH/ACGIH integrators, again using a real-world noise source.
The OSHA HC integrator reported a dose of 73 percent whereas the NIOSH/ACGIH setting reported the same noise as 272 percent.
This shows that where a number of different standards are in use, the user must be aware of the potential risk of either choosing the wrong setting before undertaking a measurement or when reviewing the reported information.
Users should ensure that the settings provided “out of the box” are those needed for their specific application and reporting requirements, and it should be clear to the user how their equipment has been configured so they can verify that it meets the requirements of the regulations under which they are working.
Users should also be able to access up-to-date and accurate information about the standards against which they are measuring and reporting noise exposures, and should be able to demonstrate that the equipment has been correctly configured to meet these needs.
We should not forget that for most users, carrying out noise measurements is just one part, and possibly a small part, of the process of managing the risk of noise induced hearing loss and creating a healthy working environment. Providing equipment that is accurate, simple to use, and easily understood should be the highest priority for instrumentation manufacturers.