Dry-Aid Kits

Question

Answer

Most hearing aid wearers should use a drying device every night, especially during periods of elevated humidity (which for many hearing aid wearers is all the time).

Hearing instruments are difficult to keep dry for many reasons, the most important of which is that they are almost sealed containers. Moisture gets inside the hearing aid through condensation, caused by temperature changes such as entering an air-conditioned room after being in warm outside air. Additionally, moisture arrives by capillary action, where ear mold tubing and receiver tubes are two common culprits. If you add perspiration and cerumen to the mix, it is easy to see why some hearing aid users have chronic - and aggravating - moisture-related problems.

While frequency of use is important, the quality of drying can be even more important in most parts of the world. In general, there are four factors that affect the rate of drying & evaporation: temperature, air movement, exposed surface area, and humidity. Except for humidity, which we want to be as low as possible, the higher the other factors the higher the rate of drying.

The highest and most thorough rate of drying, therefore, comes from a combination of high temperature, high air movement, large exposed surface area, and low relative humidity. It might be physically possible to have success with only one (i.e. elevate the temperature), but the more factors that can be integrated, the better drying will occur.

I might draw an analogy using the laundry on the line I grew up with, before affordable laundry dryers came along. Mom's laundry always dried quicker when the sun was shining bright (temperature), the wind was blowing (air movement), the relative humidity was low, and when the clothes weren't folded over or bunched up (exposed surface area).

The worst drying occurred on a cool, cloudy, windless day, with high relative humidity and clothes all bunched together on the line (lower exposed surface area). It is clear that four factors dry quicker and better than one or two.

A classic dry-aid kit operates on a single factor, and that is the reduction of relative humidity through *physical* removal of the moisture from the air - by a desiccant. Thus its quality of drying suffers considerably when compared with more active systems. It can be effective for many users in moderate climates with low relative humidity, and such kits will work better when hearing aids are left inside for long periods of time. Similarly, heated boxes normally call on only one factor, which is that warm air can hold more moisture than cool air. By raising the temperature, relative humidity is lowered, making the air inside capable of holding more moisture - so long as the temperature remains elevated.

While heated boxes or other similar devices might have a small amount of convection air flow (hot air rises), it is not enough air movement to really make a difference, unless the temperature difference between the ambient air and the heated air is very large. Heated boxes can be used with success in lower relative humidity areas, but their effectiveness drops off as ambient humidity rises. Like dry-aids, they should be used regularly for best results.

Another product I've seen combines heat with moving air from a fan, and it's efficiency should be much greater than that of either of the two types of driers previously mentioned.

Our product, Dry & Store, combines three and one-half of the four factors, working together to really increase the rate of drying. It generates controlled heat (90-95 degrees F), germicidally pure desiccated air that averages 20% RH, and it has a ball-bearing fan that produces 9 cfm of airflow that flows *around* not *into* the hearing aids. We can't increase the exposed surface area of the hearing aids (outside surface area doesn't count), but we did find a way to move a massive amount of air around inside the device while continuously removing the moisture from it with a desiccant. So, I awarded Dry & Store a half point for surface area. We strongly recommend that it be used daily, and survey results correlate frequency of use with results as reported by the user.

Finally, the important result of frequent use of a drying device is that the moisture threshold is lowered. Imagine a scale where 0 represents a perfect aid, devoid of any moisture (there aren't any 0's in real life). On the high end, 9 represents a totally failed, non-working hearing aid. My belief is that many people start out the day at level 4 or 5, even when using passive devices like dry aid kits. If level 7 represents the point at which distortion, switch problems, or other failures occur, it doesn't take long to get there from 4 or 5, even in mild climates.

The more frequently a drying device is used, and the more factors the drying device employs, the lower the start-of-day moisture threshold. Thus using a highly active appliance on a daily basis might allow a user to start the day at level 1 or 2, and thus the chance of moisture reaching level 7 is slim. So, both quantity (frequency of use) and quality (number of drying factors) are quite important.

BIO:
Rick Gilbert is a degreed chemist who has been associated with Ear Technology Corporation since its origin in 1992. He started employment there as Director of Marketing and Sales and has served as General Manager since June, 1998.