R&D Portfolio - Research Goal 2.2:
Develop hearing protection laboratory and fit-testing methods
Issue
In addition to better methods of evaluating the expected performance of HPDs, there is a need to have methods that can measure the fit and performance of the HPDs in use by an individual worker in his normal occupational setting. Although NIOSH scientists invented and evaluated the first HPD fit-testing systems in the late 1970s,[40], [41] commercial fit-testing systems were not available until the development of portable computers with high-quality sound capabilities in the late 1990s.[42] The HLR program identified the need to develop methods to estimate the noise attenuation from HPDs in the workplace and the need to validate the new laboratory subject-fit protocol7 with onsite field-testing methods.4 Because of acoustical limitations and time constraints in occupational settings, research on the measurement of a worker’s hearing threshold in those settings was needed to develop accurate and efficient testing methods. Specifically, fit-testing needs to be performed in conditions with elevated background noise levels and must be able to predict attenuation from limited data.
Approach
The HLR program pursued a coordinated effort to develop laboratory testing capabilities and evaluate potential fit-testing and rating methods. In 2000, HLR scientists met with the senior audiologist of HLI responsible for HPD development and testing to design the requirements for a new laboratory testing system based on commercially available signal generation hardware. This partnership resulted in a laboratory system (HPDLab) suitable for both ANSI and ISO testing of REAT.[43] HPDLab incorporated multiple methods for measuring hearing threshold to permit comparisons of their efficacy. The HLR program studied the performance of proposed fit-testing systems and demonstrated the equivalence of attenuation estimates between ANSI S12.6-1997 Method B and a computer-based fit-test system.14 The HLR program developed methods to estimate protected exposure levels from limited data,13,[44] and to predict the quality of a user’s fit based upon statistical classification techniques.[45]
The HLR program developed new laboratory testing facilities that have been used to develop better fit-testing procedures for workers. HPD ratings-methods research developed new techniques to characterize occupational noise exposure under hearing protectors from limited testing information. Psychophysical testing procedures have demonstrated the utility of field-testing methods.
The HLP-developed, laboratory-based HPD testing system has lowered the cost of developing new hearing protector testing laboratories. Exclusive of the cost of the reverberant acoustic testing chamber, the HPDLab system can be installed for about $15,000. A comparable commercial system would cost $80,000 or more and would still require many hours of customization work. The HPDLab has been installed in Cincinnati and Pittsburgh as well as the HLI testing laboratory.
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[40] NIOSH [1976]. A Real-Ear Field Method for the Measurement of the Noise Attenuation of Insert-Type Hearing Protectors. Cincinnati, OH: U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, HEW (NIOSH) Publication No. 76-181.
[41] Fleming RM [1980]. A new procedure for field testing of earplugs for occupational noise reduction [Dissertation]. Cambridge, MA: Harvard University, School of Public Health.
[42]Michael KL [1998]. Comprehensive use of hearing protectors: Integration of training, field monitoring, communication and documentation. Journal of Occupational Hearing Loss 1:67–74.
[43] Murphy WJ, Franks JR [2002]. Software development for NIOSH hearing protector testing. J Acoust Soc Am Vol. 112 No. 5 Pt. 2, 2295.
[44] Murphy WJ, Franks JR, Davis RR. [2005]. Field measurements of Hearing Protection Device Performance. InterNoise 2005 / Rio de Janerio, Brazil, August 6.
[45] Murphy WJ , Franks JR. [2000]. A statistical classifier for hearing protector REAT data. J Acoust Soc Am Vol. 108, No. 5 Pt. 2, 2621.