Multiple studies exist measuring hearing deficit in the testing booth (pure tone audiometry, speech recognition, HINT, etc.). However, these have not been validated in the field. Even though a deficit in function can be measured in the testing situation, effect on safe and effective performance of EJTs by the LEO has not been determined.
This is considered the boundary of normal hearing. The American Speech-Language-Hearing Association (ASHA) states that: “Screening procedures to detect unilateral or bilateral sensorineural and/or conductive hearing loss greater than 25 dB HL in the frequency region from 1000 through 4000 Hz are applicable to this age group.” (See http://www.asha.org/public/hearing/Hearing-Testing/)
In keeping with part 4.6.1 regarding the use of the least restrictive threshold for consensus statements, the Task Group reviewed the Federal Motor Carrier Safety Administration (FMCSA) standard, 49 CFR 391.41(b)(11), which is directed only to specific drivers with commercial driver’s licenses (CDL). Police physicians should not directly apply these standards to LEOs unless having a CDL is part of their job requirement. However, the Task Group is of the opinion that driving under emergency conditions is at least as demanding and has as at least as great an impact on public safety as the tasks that must be performed by drivers to whom the FMCSA standard applies. A recent report on a structured literature search commissioned by FMCSA on Hearing, Vestibular Function and Commercial Motor Vehicle Driver Safety, concluded that, at the present time, it cannot be determined if hearing impairment (defined as a hearing threshold of 40 dB or greater at 500-3,000 Hz) is a risk factor for crash among commercial motor vehicle (CMV) drivers due to an absence of studies of the specific population. FMCSA additionally found only three studies of private driver license holders (one of low quality, two of moderate quality), and concluded that: “Evidence from the private driver license holder population does not support the contention that individuals with a hearing impairment are at an increased risk for a crash.”
At the 40 dB level of hearing loss there will be a significant impairment in voice recognition. Individuals with that level of hearing loss will also have difficulty with communications, sound detection, and speech or word recognition. It is probable that some individuals will not be able to perform EJTs with hearing loss less severe than those presented in this guideline.
There are many other organizations that have published hearing standards and guidelines. However, in the opinion of the Task Group, there are no evidence-based scientific studies to support the thresholds adopted (see Appendix C for examples).
These individuals will need additional hearing evaluation (which may include full audiometric evaluation, word recognition, hearing in ambient noise testing, consultation with an otolaryngologist or an audiologist) and an individualized evaluation to determine ability to perform the EJTs. Ideally, job simulation testing should be done. Currently, no standardized test exists for this. A discussion of audiometric testing can be found at http://emedicine.medscape.com/article/835840-overview.
The NRR has been shown to be inaccurate as an index of sound attenuation, and is best used on a relative basis to compare the attenuation characteristics of various HPDs. The measurement of NRR is in flux; the current ANSI standard (ANSI 12.6-2008) specifies measurement conditions and procedures for establishing NRR.