Hybrid push-in style ear plugs

PPE - March 22, 2013 - 0 comments

Hybrid push-in ear plugs: factors that contribute to a proper fit and long-term comfort

fig0From experience, we know that most people do not properly fit their ear plugs and often compromise protection for personal comfort. This may be unintentional (lack of training in obtaining a proper fit), or at times may be intentional (to improve speech intelligibility, or to improve comfort, for example).

Without proper fit training, ear plugs, especially roll-down foam models, are not intuitive to use. Without a proper fit, users do not achieve optimal attenuation for their environment, are under protected and are at further risk of noise-induced hearing loss. Using ear plug fit testing technology, the correlation between improper fit and poor attenuation is easy to measure.

In candid conversations with safety managers and other Hearing Conservation professionals, a common thread identified that roll-down foam ear plugs are a challenge for workers:

  • “Our employees don’t take the time to ‘hold’ the ear plug in their ears while the foam expands.”
  • “It is not inserted properly because the ear plug is too big for their ear canal.”

To address the problems created by non-intuitive insertion and lack of training for roll-down foam ear plugs, a new style of no-roll foam ear plug that is pushed in like a multiple-use model has been introduced over the past few years. These “push-in” style ear plugs combine a firm stem with a foam tip, and do not require rolling prior to insertion. This style of ear plug takes little time or effort to fit, and

since it utilizes foam, it claims to deliver a higher degree of comfort. Such ear plugs are marketed as a “hybrid” between a single-use (foam for comfort) and multiple-use ear plug (easy insertion and reinsertion for cost-effectiveness), and priced at the low end of multiple-use ear plug spectrum.

In developing Howard Leight’s® new hybrid push-in style ear plug Pilot™, we looked at the factors that deliver improved fit and comfort in this category, including material composition, the amount of foam and stem (“Foam/Stem Ratio”), attenuation and variability of fit.

Material composition

Variability in cell structure relates directly to product performance. With a variety of cell sizes on the inside of polyurethane foam ear plugs, expansion pressure inside the ear canal is reduced, and an ideal, gentle expansion rate is achieved. With smaller, closed cells toward the outside surface of the ear plug, a smooth skin improves insertion (less friction between the ear plug and ear canal). The smooth skin is also more hygienic, resisting dirt build-up, and is easier to clean.

Microscopic photography on two push-in style ear plugs was conducted.

Figure 1. Microscopic photography of push-in foam ear plug cross-sections at 55x magnification

fig1.1 Pilot_X-Section_200fig1 Yellow_Xsection_200In Figure 1, we zoomed in on a cross-section of two push-in style ear plugs that are commercially available. The cells of the ear plugs on the left varied in size and structure throughout the entire ear plug. When this ear plug is inserted in the ear canal, this varied cell structure expands at different rates resulting in a more gradual and gentle expansion rate. Once expanded, the variable-sized cells exert less pressure inside the ear canal. In comparison, the foam cell structure of the ear plug on the right is more uniform and less flexible when compressed, so expansion rate is faster and expansion pressure is greater inside the ear canal. Over several consecutive hours, this in-ear pressure may feel very uncomfortable to the wearer.

In analyzing the skin of these ear plugs (Figure 2), we see the ear plug on the left utilizes a closed cell smooth surface on the outside. This enhances its resilience against dirt buildup. On the ear plug on the right, there is a jagged, open outside surface collects dirt and other contaminants more easily.

Figure 2. Microscopic photography of push-in foam ear plug skins at 35x magnification

fig2 Pilot_Skin_200Product composition: foam/stem ratio

Aiding the insertion of nearly all push-in style ear plugs is a molded stem along the central axis of the ear plug. This stem helps to glide or “navigate” the ear plug into the ear canal quickly and easily for a proper fit without rolling down the foam, and helps ensure a good, consistent fit.

While the stem may facilitate fast and easy insertion, many wearers claim that the hardness and size of the stem irritates the inside of their ear canal, producing a “skewering” sensation inside their ear canals. Discomfort appears to increase for multiple insertions or longer wear times. The hard stems are often large in cross-sectional diameter relative to the overall ear plug cross-sectional diameter, and often protrude past the outer ear, interfering with other PPE equipment.

We analyzed the two-part composition (the “Foam/Stem Ratio, or “FSR”) of several other push-in style ear plugs (Figure 3). The FSR represents the content and weight of an ear plug’s components. With hybrid push-in ear plugs, we analyzed the foam tip and insertion stem. Pilot’s FSR has more foam (80% foam) in its construction than the other push-in style ear plugs. Only Peltor Next’s No-Touch push-in ear plug came close in its FSR, with 60% foam in its overall construction.

Figure 3. Foam/stem ratio (FSR) of push-in style ear plugs

fig3 Foam_Stem_Ratio_500Attenuation

A push-in style ear plug should, by design, be easy to fit with minimal training. Recently, ten untrained test subjects were invited to test the fit of different push-in products. These test subjects were recruited from the public, and had no prior experience using ear plugs. We provided no training to them prior to their fitting of these ear plug samples, rather simply supplied them with the ear plugs and the instructions found on the package of each product. Results for attenuation tests are shown in Figure 4. Attenuation at each frequency band is shown for three push-in ear plugs: Howard Leight Pilot, E-A-R Express Pods, and E-A-R Push-Ins.

Figure 4. Attenuation comparison

fig4For untrained users, the results show that Pilot was found to have significantly higher attenuation (more protection from hazardous noise) than the two competitive push-in products. This implies that the insertion of the Pilot ear plug is more intuitive, and it is easier to get a good fit with Pilot than with other competitive push-in models, particularly for untrained users.

Variability of fit

Another desirable quality in an ear plug is consistency of fit, not only between many users, but also within repeated fittings by the same user. In other words, a good ear plug will perform consistently for repeated fittings, and not vary significantly from one insertion to the next, or from one user to the next.

In the acoustic lab, variability of fit is measured by testing a variety of users several times, and then measuring the variability (standard deviation) between those users to determine if there are significant outliers. An ear plug that has high variability among different users and different fittings will have high standard deviations. These standard deviations are printed on the box or bulk packaging of all hearing protectors so that users might judge which hearing protectors have lower standard deviations, and thus provide the most consistent fit.

Figure 5. Variability of push-in ear plug fit

fig5 Variability_FitConclusion

At the conclusion of their acoustic lab testing, and after spending several hours wearing each of the push-in style ear plugs for multiple trials, test subjects were subjectively asked to rate each ear plug based on ease of insertion and overall preference. Pilot was identified by users to be easier to fit than conventional roll-down foam ear plugs, and overall, more users preferred Pilot than other push-in style ear plugs by a 2-to-1 margin.

Foam is a great attenuator and provides maximum comfort when properly fit, and is an ideal choice for a hearing protection device. But foam is not always easy to fit, due to the roll-down requirement and variability in expansion rates. Foam with an insertion aid such as a stem, eliminates the need for roll-down and improves fit, but the stem can significantly decrease the comfort of an ear plug if the foam/stem ratio is too low.

The Pilot ear plug, with its high foam content, enhanced wear time characteristics, and flexible, low-profile collapsible stem for insertion, is an ideal solution for those who seek a push-in style ear plug that is quick to insert, and maximizes overall fit and comfort.

Click here to download a PDF of this case study

Click here to learn more about the Pilot push-in earplug

HearForever(R): A initiative by Honeywell Safety Products/Howard Leight, www.hearforever.org.

Published with the kind permission of Howard Leight/HearForever.

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