Measuring hearing protection
Answered by Jeffrey Morrill, president, CavCom Inc., Walker, MN.
A variety of "fit test" training programs have emerged in recent years to demonstrate the amount of protection achieved by the personal method of hearing protection device insertion and use. These programs are valuable training tools, as they can assist in selecting the type of protection that works best for the employee, can be administered by plant personnel and add to the practicality of the procedure. Although these are "point-in-time" procedures that leave day-to-day compliance up to the employee, they are good training and fitting tools. In the final analysis, only annual audiometric testing will provide an objective picture of employee motivation and participation on a daily basis.
There are also objective measures of determining if employees achieve a positive seal with their HPD. One method is to monitor employee exposure through noise dosimetry, where a microphone is placed in the hearing protection device, thus measuring the noise levels in the ear canal versus the background noise levels. Another method is to perform an acoustic fit check with the employee's two-way radio and HPD communication ear set inserted. The absence of an acoustic "squeal" and radio transmissions that are free from background noise prove the HPD has a good seal.
Many companies require double protection (insert HPD plus an earmuff) in work areas over a certain decibel level, typically 100 dB or greater. The rationale is that a single hearing protector may not provide sufficient hearing protection at these exposure levels, and the addition of the second HPD will ensure adequate protection. Although the additional noise reduction of the earmuff will help somewhat, the insert hearing protector remains the critical protection device, particularly when safety glasses, long hair or other personal protective equipment prevent a good seal between the head and muff. When double protection is used, employee training programs and objective methods of monitoring are even more important because the supervisor cannot observe if the protection device is inserted properly under the muff, as shown in the image.
The amount of hearing protection should match the demands of the environment to ensure employees can understand important verbal instructions, warnings or machine cues. For example, 30 dB of HPD performance is probably too much noise reduction in moderate noise areas (less than 90 dB) and may, in fact, impair the worker's ability to hear important signals. However, 30 dB of HPD noise reduction may not be enough to protect the worker and enhance the ability to hear warnings in areas of 110 dB or more.
The employee's hearing ability is also a factor because the ability to understand speech diminishes with hearing loss. If verbal communication is a critical demand for safety and productivity, it is important to match the level of protection or assistive listening device to the individual's needs.
For example, requiring employees to wear welding protective lenses for normal daylight operations would be counterproductive. By the same token, using standard UV sunglasses for welding operations would be equally inappropriate. Unfortunately, ears do not demonstrate immediate pain or loss of sensitivity to exposure as eyes do; therefore, we must depend on both common sense and science to match hearing protection needs to the demands of the job.
One thing is certain: When routine changes to urgency, employees need the best tools available to react and communicate clearly to avoid crises. It is better to "tune up" the hearing protection to the communication needs before the incident, for safety's sake.