According to Environmental Protection Agency (EPA) regulations, ANSI S3.19-1974 is the current testing requirement for hearing protective device labeling. 10 human subjects are required for hearing protector evaluations using 9 test freqiencies. The Noise Reduction Rating (NRR) is calculated from these data. Exact labeling requirements can be seen at:
http://www.gpo.gov/fdsys/pkg/CFR-2003-title40-vol1/content-detail.html