How to Use the Search Engine

This compendium was designed to be actively used on the Internet. It has a search engine that identifies protectors by type, manufacturer, features, desired Noise Reduction Ratings (NRR), or by inputting noise exposure levels in dBA or octave-band levels.

To see all of the products in the database, simply leave the Product Type field set to “All Types,” leave the Manufacturer field blank and click on the Search button. The products will then be displayed in alphabetical order by manufacturer and by product within manufacturer. Shown will be the company, product name, product model, and NRR. To learn more about a product, click on the photograph of the product and you will be taken to the product’s page. The product page will display the photograph, if available, the feature descriptions provided by the manufacturer, the test data if available, the name of the testing laboratory, the NRR, as well as a link to the manufacturer’s web site.

This general search can be made more specific by selecting a particular protector type - earmuffs, earplugs, custom molded earplugs, or semi-inserts. Products for any manufacturer may be searched by selecting the manufacturer’s name and then by selecting all types, earmuffs, earplugs, custom molded earplugs, or semi-inserts. The results pages will appear as they did for the general search, but will be limited only to those products that meet the search criteria.

If a product with a particular NRR is desired, the NRR can be entered for: 1) a general search, 2) a search for product type, 3) a search by manufacturer, or 4) restricted to a certain product type and a specific manufacturer. When searches are based on the NRR, the returns are those protectors with NRRs within a 3-dB range of the requested NRR. It is possible for this type of search to have no returns because there are no products in the database that meet the search criteria.

While it is possible to search for protectors based on noise exposure levels instead of NRR, it is not possible to search for a given NRR and a noise exposure level since exposure level determines the necessary NRR. Exposure levels may be entered as noise level in dBA or octave-band levels. When this search strategy is used, the protectors returned from the search are based on the derated NRR to provide a protected exposed noise level (ENL) between 75 and 85 dBA. When octave-band noise levels are entered, the calculations are based on NIOSH Method 1 from the original noise criteria document (Criteria for a Recommended Standard: Occupational Exposure to Noise, DHHS (NIOSH) Publication No. 73-11001). When the exposure level is entered in dBA, the calculations are based on the NIOSH revised noise criteria document (Criteria for a Recommended Standard: Occupational Noise Exposure Revised Criteria 1998. DHHS (NIOSH) Pub. No. 98-126). Regardless of now noise levels are entered, the derating of the hearing protectors’ labeled NRRs is performed using the NIOSH derating schemes as described in the NIOSH revised noise criteria document. This search is based on the derated NRR because research of NIOSH and others have found that the NRR on the label of the product is consistently much greater than the “real-world” noise reduction performance of the product due to the test methods required for hearing protector labeling.

The NIOSH derating procedure and how the derated NRRs are applied are described in the revised noise criteria document and shown here as well:

NIOSH recommends that the labeled NRRs be derated as follows:

Earmuffs:Subtract 25% from the manufacturer's labeled NRR
Foam earplugs and custom molded earplugs:Subtract 50% from the manufacturer's labeled NRR
All other earplugs including semi-inserts:Subtract 70% from the manufacturer's labeled NRR

For example, measure noise exposure levels in dBA with a sound level meter or noise dosimeter, the effective A-weighted ENL is:

ENL = dBA - (derated NRR -7)

When the noise exposure level in octave bands is known, the noise exposure level in dBC is calculated and then the ENL is:

ENL = dBC - derated NRR

The 7-dB correction applied to exposure levels when measured in dBA is based on the assumption that there will be a 7-dB difference in the C-weighted and A-weighted measures of the same noise. When that is indeed true, the search results for noise levels entered in dBA and in octave-band levels will be identical. However, for most noises, that will not be true and the search results for the two noise-entry options will yield different listings of devices. When octave-band data are available, the search results will invariably yield the best listing of applicable products.

If a manufacture has provided a subject-fit NRR for a product derived by testing according to Method B of ANSI S12.6-1997, the subject-fit NRR will be used in the search without any derating applied whether noise levels are entered in dBA or as octave-band levels. However, noise levels entered as octave-band levels instead of noise levels in dBA when applied to subject-fit NRR data will yield the best possible search in terms of showing product with the best capability of protecting hearing from damage due to noise exposure without over protecting and isolating the person wearing the selected hearing protector.

Even though the derated NRR is not a replacement for noise reductions based on subject-fit data in accordance with ANSI S12.6, Method B, NIOSH believes the derated NRR ( provides a better estimate of how the protector will typically perform for most wearers. This problem should be resolved when the new ANSI S12.6-1997 Method B is used to rate noise reduction performance.