Most foundries have some high noise areas requiring hearing protection. OSHA dictates employers have a hearing conservation program if employees are exposed to an 8-hour time-weighted average (TWA) at or above 85 dB(A), and then requires hearing protection be worn at or above a 90 dB(A) TWA. NIOSH recommended practices push those limits even lower, requiring a hearing conservation program at or above 80 dB(A) TWA, and hearing protection at or above 85 dBA TWA. An industrial hygienist or trained safety professional can measure noise levels with a noise dosimeter. A noise dosimeter is hung on representative employees and records noise levels throughout their shift, then calculates the TWA. Records of the results should be kept, and all employees notified of their results. An employer can also map noise levels in the facility and make hearing conservation decisions based on area noise levels. It can be helpful and cost effective to use a phone app to get an idea of where noise levels are high, so the IH professionals can be guided to potential trouble areas.
When noise levels are at or above 90 dB(A), you’ll need the following: Annual audiograms—These hearing tests help track any hearing loss that may be occurring so the employer can intervene with better hearing protection devices and/or retraining. Audiograms should be administered by an occupational hearing conservationist (OHC), credentialed by the Council for Accreditation in Occupational Hearing Conservation (CAOHC). Audiograms can be done at clinics, in mobile vans, and in onsite sound reducing booths. The OHC should be supervised by an audiologist or medical doctor who is a CAOHC trained Professional Supervisor of Audiometric Monitoring Programs. New employees should have a baseline audiogram within six months of starting their high noise job unless a mobile test van is used, in which case the audiogram may be conducted within one year of starting in the job. Note that it’s in the employer’s best interest to get the baseline audiogram as soon as possible to document if a new employee arrives on the job with compromised hearing. OSHA requires employers to conduct baseline audiograms within six months of an employee’s first exposure at or above the action level, and employees may not refuse an audiogram. For this reason, some employers have found it is easiest to inform prospective employees audiograms are a condition of employment. Concerning employees who are legally deaf or have significantly impaired hearing, they also must receive baseline audiograms and must wear hearing protection where noise levels equal or exceed 90 dB(A) to preserve whatever hearing may remain.
Follow-up procedures for problem audiograms—A loss of hearing averaging 10 decibels or more relative to the baseline test (in certain pitches in one or both ears) is known as a standard threshold shift (STS). If the annual audiogram shows a STS the employee may be retested within 30 days to determine whether the shift is persistent. If the STS remains at the retest, then the audiogram may be reviewed by an audiologist, otolaryngologist, or physician to determine work relatedness, which may also require a medical questionnaire or a visit to the doctor. If the STS is determined to be work related, it must be recorded on your OSHA 300 log.
Engineering controls—Hearing protection devices are PPE, and engineering controls are always better than PPE. For this reason, OSHA requires employers to evaluate engineering controls to reduce noise hazards. Controls determined to be “feasible” must be implemented, even if they don’t reduce noise levels enough to remove the hearing protection requirement.
Training—Employees must receive training about noise and hearing loss when assigned to a high noise job, and annually thereafter. This training should include: the effects of noise on hearing; the purpose of hearing protection devices and the advantages/disadvantages of the different types; instructions on selection, fitting, use, and care of the hearing protection devices; and the purpose of audiometric testing and an explanation of the procedures. If an employee has a work-related standard threshold shift, they must be refitted and retrained in the use of hearing protection devices.
Use and selection of hearing protection—It’s not a good idea to grab just any ear plug or ear muff and call it good. Different hearing protection devices have different noise reduction ratings (NRR). The NRR tells you how much noise the protector blocks. Plugs are nearly always better than muffs since they seal better when worn properly. Select a hearing protector with an NRR high enough to reduce the noise that reaches the ear to below 85 dB. OSHA “derates” hearing protection because many people don’t wear it properly. The formula (NRR-7)/2 will give you the effective hearing protection level. For example, a hearing protection device with a NRR of 33 gives you 13 dB of protection [(33-7)/2] so they can be worn in noisy environments up to 98 dB(A). If a plug doesn’t provide enough protection for your environment, extra protection can be accomplished by wearing an ear muff over a plug. This adds only 5 dB of protection regardless of the muff’s NRR.