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High airflow hand dryers are found in many public restrooms today. These dryers offer quick and clean hand drying, and are seen as being an environment-friendly alternative to paper towels. However, many new hand dryers are loud, exposing individuals using the facilities as well as those employees who clean the facilities to potentially dangerous noise. Prolonged exposure to high levels of occupational noise can cause damage to hair cells in the cochlea, resulting in varying degrees of noise-induced hearing loss. This study examined the intensity (in dBA) of the noise produced by the air dryers in campus restrooms. Hand dryer peak and average noise was measured with a sound level meter at 2.5 ft, 5 ft, and 10 ft from the dryer. Noise measurements did not decrease as predicted by the inverse-square law, probably because of the reverberative surfaces found in the restrooms. The small sample of hand dryers tested was mostly found to be producing more noise than the manufacturer claimed they would; indeed, none of the dryers would be safe for an 8-h workday exposure. While hand dryers do reduce paper trash, they pose as a different sort of hazard to our environment and population.
Air-powered hand dryers in public restrooms have become more common in recent years, replacing paper towels in many settings. This change results in less trash, but the noise generated by hand dryers is often found to be noxious and extremely loud. In a large restroom, such as at an airport or a casino, where many hand dryers are often in operation at once, and the workers might clean one restroom for the majority of their workday, the noise generated can reach dangerous occupational levels. In this investigation, the researchers measured the intensity of sound produced by hand dryers on campus at 2.5 ft, 5 ft, and 10 ft from the source and compared these measurements to manufacturers’ data and occupational safety agencies’ recommendations.
Occupational noise is a known health hazard because it can lead to noise-induced hearing loss. According to the Occupational Safety & Health Administration (OSHA) of the United States, workers should not be exposed to more than 90 dBA in an 8-h shift. The National Institute for Occupational Safety and Health (NIOSH) mandates that workers should not be exposed to more than 85 dBA in an 8-h workday. Many countries around the world have a similar policy to that of NIOSH, based on the World Health Organization (WHO) recommendations. However, subtle changes in speech perception have been reported in workers exposed to only 80 dBA, even though they were within the normal limits on a pure-tone hearing test. Train operators were given a battery of auditory tests, and compared to a control group without noise exposure. They scored significantly more poorly on a test of duration patterns, and on perception of sentences presented with 4-talker babble at a signal-to-noise ratio of -5dB. In light of this, these current recommendations may be too liberal.
Restroom patrons use the hand dryers at an arm's length, obviously, which we estimated to be 2.5 ft. However, daily experiences showed that the dryers were informally perceived as overly loud by patrons far across the room as well. Based on the inverse-square law, it would be predicted that the intensity at 5 ft would be 6 dB less, and at 10 ft, 12 dB less. If the sound was attenuated in this way, it might reduce the risk to maintenance workers; thus, the dryer output was measured at these three distances. The patrons may find the dryers annoying, but for the workers, the hand dryers have the potential to be dangerous.
Manufacturers of hand dryers provide specification sheets, installation manuals, and sell sheets for their products where one might expect to find clear information about the predicted sound intensity produced by their various models, as this might enable comparison shopping when planning a public washroom. Dyson publishes a sound power level of their dryers on the technical specification pages for each model. Their newest model is purported to produce 81 dBA, but the model studied here is rated at 85 dBA. Information from other manufacturers was not listed clearly on the specification sheets. Sound level measurements for the Excel Dryer's XLERATOR were in a separate document, which states that the dryers operate at 78-80 dBA, but as high as 90 dBA if the hands are held in a particular way. Their measurements were taken at 5 ft from the nozzle. The specification sheets for World Dryer's Airforce only stated that the dryer had a “low sound level.” Upon writing to the company, it was intimated that Airforce operates at 80 dBA without hands and 88 dBA with hands (e-mail communication, Eileen Malloy, January 3, 2014). The reported duration of a drying cycle for the three above mentioned dryers were 10-15 s, 12 s, and 12 s, respectively.
The researchers measured the noise level in campus restrooms at a distance of 2.5 ft (approximately at an arm's length as one would use the dryer), 5 ft, and 10 ft (space permitting). Measurements were taken with a digital sound level meter, model #33-2055 from RadioShack. This sound level meter is accurate to ±2 dBA. The researchers measured each hand dryer three times at each distance, taking the average reading for one drying cycle in each trial. Measurements were taken in eight restrooms and included three different manufacturers’ products.
For each of the eight hand dryers, the mean of the three average sound level measurements was calculated at each distance from the source [Table 1 and Figure 1]. Based on the inverse-square law, one would expect a 6 dBA drop at each doubling of distance, however, this was not the case. The mean intensity for all the readings at each distance was also calculated, and found to be 87 dBA at 2.5 ft (from the dryer), 84 dBA at 5 ft away, and 82 dBA at 10 ft away. The most intense sound recorded across all the trials was 91 dBA, and the least intense was 80 dBA.
Measuring the sound output of restroom hand dryers confirmed what many have commented on anecdotally: These dryers are loud. On the whole, the dryers studied in this investigation produced more intense sound than predicted by the manufacturers, and the reverberations produced in the bathrooms reinforced the intensity even at 10 ft from the source of the sound. At all the distances measured, a full-day exposure at work could damage overall hearing and speech perception in particular. People who work in maintenance positions, judged to be within compliance for noise exposure, may find themselves with an additional source of noise when bathrooms are installed with hand dryers rather than the earlier use of paper towels. Employers with hearing conservation programs should add these hand dryers to their list of possible harmful sources of noise. Multiple dryers running at once, an event that was not tested in this study, would result in an increased sound intensity, estimated to be 6 dBA more for each doubling of the number of machines, adding to the burden on workers’ ears. Employers might consider deploying sound dosimeters to actually test the exposure of workers over the course of a workweek, to see if intervention is necessary in specific workplaces.
Future studies should include a larger sample size of hand dryers, installed in various locations, to continue the comparison between the field data and the manufacturers’ reports. Additionally, it would be worthwhile to measure how long employees and restroom users are exposed to dryer noise, and at what intensities. It may also be important to study how the patrons actually use the dryers. Do they run them for two cycles, or just a few seconds? Different hand postures while drying can also affect the sound level produced and could affect the noise exposure for nearby workers.
Perhaps methods to reduce noise exposure from hand dryers are on the horizon; however, many currently installed loud dryers are in service and are likely to remain so for years. They are typically sold with a 5-year warranty,[5,8] but can have a much longer service life. As our communities reduce the use of paper towels, a noble pursuit, they inadvertently increase the assaults on our ears. The full cost of this trade-off is yet to be determined.
Thanks to Caroline Malizia and Lindsay Miller for their contributions to this work.
Source of Support: Nil.
Conflict of Interest: None declared.