If noise levels in your lab exceed 85 dB, engineering or administrative controls are required to reduce the risk of occupational noise-induced hearing loss. If you think your lab has harmful noise levels (e.g. if it is difficult to carry on a conversation), contact the Safety Office at ext. 33587 for an assessment. The Safety Office will do sound measurements and recommend the method and amount of attenuation required and the available types of hearing protection.
Engineering controls such as sound absorbing panels or enclosure of the noise source can greatly reduce noise levels.
Administrative controls such as limiting the amount of time workers are exposed to excessive noise are also effective.
The use of Hearing Protection Devices (HPDs) may be necessary to reduce personal exposure to excessive noise. This could be in the form of:
- Earplugs (including semi-inserts)
- Helmets, with or without electronic communication capabilities
Every HPD has a Noise Reduction Rating (NRR) typically ranging from about 20-30dB. Due to variability and improper insertion when looking at the NRR of a HPD you should derate the value by about 50% for earplugs and about 30% for earmuffs.
Earplugs are placed in or against the entrance to the ear canal to form a seal and block sound. They can generally be categorized as foam, push-to-fit, premoulded, formable, custom-moulded, semi-insert and semi-aural styles.
- Foam, or “roll-down”, earplugs need to be rolled-down between forefinger and thumb and then inserted into the ear canal and allowed to expand. These are general disposable and only get a few uses. Sanitation can be an issue as dirty hands can contaminate the plug.
- Push-to-fit generally are made of foam and have a flexible stem that is used to insert the plug using a twisting and pushing motion. These plugs have a somewhat longer life-span and are more sanitary because they do not need to be rolled-down.
- Premoulded earplugs are made of flexible materials and various shapes. They have a flexible stem for handling and insertion and they have a considerably longer life-span than foam plugs.
- Formable earplugs are made of malleable materials and are typically use once and sold to consumers for use in recreational settings (music concerts). They are not commonly used as part of a Hearing Loss Prevention Program.
- Custom-moulded plugs can be moulded in place and be ready for use within 5 minutes or they can be “lab-produced” where the mould is sent to a lab for final manufacture. Both generally provide a good fit and last a long time if cared for properly.
- Semi-insert and semi-aural ear plugs are also known as banded plugs. They have soft tips that are held in place with a lightweight, spring-loaded band. These styles are ideal when earplugs are repeatedly removed and inserted.
Most earmuffs are rigid moulded plastic earcups that seal around the ear. They generally provide the best protection but can be bulky, hot and uncomfortable to wear. There are models that attach to hardhats; if these are used they need to be approved for use by both manufacturers.
Helmets enclose a substantial portion of the head and are usually designed primarily for impact protection. They are not commonly worn in occupational settings; they are more likely to be found in recreational and military settings.
Modification of Hearing Protection Devices
Modification of HPDs is not permitted. This seriously compromises their effectiveness. Modification includes, but is not limited to;
- Drilling holes in earcups
- Reducing headband tension of muffs
- Trimming or removing flanges
For sound exposure levels above 105dB the use of a single HPD will likely be insufficient to reduce the exposure to below 85dB. In these cases double protection (or dual protection) can be used. Typically this is wearing earplugs and earmuffs together. When calculating how much to derate the NRR of both devices you use the device with the higher NRR to calculate the derating value using the following formula;
L - [(NRR+5)(0.65)-3] = XXdB
L=measured background noise in dBA
For example: Background noise is 105 dBA, earplug NRR is 33, earmuff NRR is 26. We use the earplug NRR of 33 because it is higher. So,
105 - [(33 + 5)(0.65) - 3] = 105 – [24.7 - 3] = 83.3
Which rounds to 83 dBA.
Personal Music Devices
Listening to music using earbuds can cause hearing loss if listened to at high volume. Many devices have safety features built in to limit the output of earbuds to less than 85 dBA. However, these features can be easily turned off. The use of these devices in areas with loud background noise can actually be more detrimental to hearing as the user will often turn the music up louder to be able to hear it better.
Departments and supervisors are responsible for ensuring that their workers are not listening to music at levels above 85 dBA. Departments and supervisors may also ban the use of earbuds if deemed necessary.