Posted By David Whaley
Is there anyone who can help?

Recently we received a complaint from a group of school children who were on a tour of the factory about noise in a department. The noise level in the department is typically 65 dB(A). It tuned out the noise they were complaining about came from ultrasonic cutters.

Octave band analysis reveled 90/91 dB at 16khz. Can anyone advise or point me in the right direction as whether this could harmful. It is outside the hearing range of our workers.

Thanks

David

Posted By Paul Leadbetter
David

When you say that the noise level is typically 65 dB(A), is this expressed as an 8-hour Leq? If so, and the ultrasonic noise has been taken into account already, then there is no problem.

Paul

Posted By RoseR
Part of my brain, that is still working on a Friday, seems to recall something in the news in the last 6 months or so about a device that emits a high pitched noise, that was been used by some shopkeepers to ensure that teenagers do not gather in large numbers outside their shops.

I'm sure it worked on the basis that the pitch emitted was one that could only be detected by children/young adults and was extremely annoying to them, therefore they didn't hang around outside the the shop because of it.

Maybe a similar thing?

Posted By David Whaley
Paul,

It is a short term Leq, i.e. long enough for the meter to give a stable reading. It is also a straight liner reading not 'A' weighted, although the 'A' filter does not make a big difference at higher frequencies. I would estimate the machines are running for a minimum of six hours out of a eight hour shift.

David

Posted By Joan Blease
A lot of good information already posted. When we test hearing we test the frequencies 500hz to 8KHz - these are known as the speech frequencies. When I was with the NHS we would test 500Hz but it is not a requirement for industry and HSE Categorisation.

16KHz is at the upper rang of what we can detect and I agree that as we age we loose the ability to hear high pitched noises. It's called Presbyacusis (usually known as senile deafness) if you are interested.

If the noise level is 65dB it is around the decibel level at which most of us speak (usually quoted as being 60dB).

Although hearing tests are a good idea the audiometer only "goes up to" 8KHz so would not detect any deterioration at 16KHz. I am not aware of any audiometer that tests frequencies over 8KHz - but I would be wrong

Email me if you want any more info on ears/hearing

Posted By David Whaley
Adrian,

Why do say it is unlikely to to be generating 90 db at 16khz for 6 hours? The machine does not have a cycle as such. It runs continuously, the noise is generated by ultrasonic cutters that are running the whole time the machine is running. Yes the machine does stop to change rolls etc. hence the estimate of six hours out of an eight hour shift.

My original question, which seems to have been bypassed by some, is does the noise at this frequency pose a risk to people working in the area. Even if they cannot hear it. Comments made by some suggest not. What I am looking for is any research or guidance that can confirm or otherwise.

Perhaps I am looking for something that doesn't exist. But I do get concerned when these issues are raised.

Thanks

David

Posted By Granville Jenkins
I have a problem - The maximum allowable sound pressure levels(SPL) for industrial audiometry are as follows:

Frequency 31.5Hz, 76dB without noise excluding headset (wneh) - Maximum SPL with noise barrier headset (wnbh) 76(dB)

Frequency 63Hz, 61dB wneh - 61dB wnbh

Frequency 125Hz, 46dB wneh - 55dB wnbh

Frequency 250Hz, 31dB wneh - 44dB wnbh

Frequency 500Hz, 7dB wneh - 31dB wnbh

Frequency 1000Hz, 1dB wneh - 31dB wnbh

Frequency 2000Hz, 4dB wneh - 43dB wnbh

Frequency 4000Hz, 6dB wneh - 50dB wnbh

Frequency 8000Hz, 9dB wneh - 44dB wnbh

I do not profess to being a sound analyst, but going by what has been mentioned there is obviously a problem and I would recommend that that the services of a company specialising in industrial audiometry are consulted.

I have done a quick internet search and suggest viewing the following site: www.hsmc.co.uk/noise html

Regards
Granville

Posted By John Murgatroyd
I have done extensive searches on this matter in the recent past. There are several research papers on hearing loss connected to high frequency sound exposure. One of the [easiest] to read: http://www.hse.gov.uk/re...rr_pdf/2001/crr01343.pdf

"Over the frequency range 10-20 kHz, the MPLs were set at band levels in the range 75-85 dB,
to avoid unpleasant subjective effects such as annoyance and auditory discomfort, tinnitus,
balance disturbance, persistent headaches, fatigue, malaise and even nausea. A structured survey
of effects, linked to measured VHF band levels, would be helpful in confirming (or otherwise)
these long-established MPLs for unprotected ears. A second aim might be determination of the
prevalence of unpleasant subjective effects at various levels of VHF or ultrasonic noise; this
might be thought of as work towards a dose-response relation describing adverse subjective
effects"