Monday, June 01, 2009

AUDIOMETRIC TESTING - what you should know

Today is 'Gawai Dayak' Day in Sarawak, so we have Public Holiday for two days(1st & 2nd June). I would like to wish all my friends who celebrate Gawai - Selamat Ari Gawai - Gayu Guru Gerai Nyamai
I am now in the midst of reporting audiograms of workers from few industries.
What is audiometric testing? Have you done one ?
AUDIOMETRY is the testing of hearing ability. It is done using audiometer(see second photo above) and the person tested must be in silent booth. FMA (Noise Exposure) Regulation 1989, recommends to use a pure tone audiometry (PTA) (air conduction) at 500, 1000, 2000, 3000, 4000 & 6000 Hz each ear separately. The worker must have a minimum prior quiet period for 14 hours.
A lot of workers exposing to noise has high frequency hearing loss ( A dip in the above audiogram at 4000 Hz). From the audiogram we can determine hearing loss, hearing impairment and standard threshold shift (STS). A terminology used in the regulations.
Hearing loss is defined as hearing threshold of equal or more than 25 dB(A) at any frequency. *The above audiogram shows that the worker has hearing loss (45 - 55 dB for both ears (O label for right, X label for left) at 4000 & 6000 Hz.
 Hearing Impairment is an average permanent hearing threshold at 500, 1000, 2000 and 3000 Hz shifted 25 dB(A) and above.
STS on the otherhand is an average shift of more than 10 dB at frequency 2000,3000 and 4000 Hz relative to baseline audiogram in either ear. STS can only be identified by comparing the current audiogram with the previous baseline audiogram.
STS can be of two types : temporary (due to hair cell fatigue) or permanent ( due to hair cell atrophy). In order to declared the STS is permanent (PSTS), an audiometric testing must be repeated in 3 months (a requirement in FMA (Noise Exposure) Regulation 1989).
Tips: As a simple rule of thumb, you can find out whether you have STS or not by the doing this simple test. When you drive to your workplace in the morning, switch on your car radio to the volume level that you can hear. When you park your car, switch off the radio BUT dont change the volume level. When you go back home in the evening  switch on your radio with the previous volume level in the morning, if you cannot hear the radio at this previous volume level, that means you experience STS.
Three problems I always encounter in audiometric testing are (take note SHO) :
1. The worker does not bring  the previous audiogram (?employer fault) ; therefore cannot determine STS
2. The worker does not in prior quiet period for 14 hours, some of them come to do the audiometric testing immediately after their night shift, therefore the audiogram if done is not reliable
3. The worker does not know the noise level at their workplace. Therefore difficult to recommend the frequency of next audiometric testing ( 2 yearly for those who expose to noise at action level but less than PEL( 85 dB - 89 dB(A)). Annually for those who expose to noise at or above PEL(90 dB(A)) or with problem in their hearing ability). 
**Action level = 85 dB(A), PEL (Permissible Exposure Limit) at 8 hours TWA= 90 dB(A)

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