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Standards Info

How is hearing protection tested in Australia and what standards apply?

The SOUND LEVEL CONVERSION (SLC80) rating as applied to hearing protection devices (HPD) is a simple number and class rating derived from a test procedure outlined in the Australian/New Zealand Standard, AS/NZS 1270: 2002.

It provides a simple number guide to the level of noise attenuation (reduction) that can be expected from a particular HPD.

Because humans are different, the level of protection achieved for each person could also be different and so a scientific formula is used to allow for differences.

The SLC value includes a correction to ensure that the stated degree of noise reduction is obtained on 80% of occasions. Hence the SLC80 rating. The SLC80 rating is the difference between the sound level of the environment in which the HPD is worn and the sound level reaching the wearer’s ears.

The testing procedure can be separated into two different areas:    

1) Mechanical Testing:

Where the device is subjected to physical forces, stretching, heating and concussion - to simulate real wearing conditions over a period of time.

2) Audiometric Testing:

This is a subjective test. A minimum number of human test subjects are selected at random and given a hearing test to establish if they fall into the category of "normal hearing", as outlined in the standard. The attenuation of the HPD is determined by measuring each subject’s hearing threshold with and without the HPD fitted. The difference between these two thresholds is the so-called real ear attenuation of the HPD to a variety of frequencies.

In simplistic terms, from this data the mean real ear attenuation and standard deviation (variation) at each frequency is calculated. The mean minus standard deviation, when subtracted from the band level gives the attenuation.

HPD are also given a class rating, as outlined below, once the SLC80 rating is known, and refers to the level of noise attenuation achieved by each device. The higher the rating, the greater the efficiency of the hearing protection device.

 CLASS SLC80dB 
 1  10 to 13
 2  14 to 17
 3  18 to 21
 4  22 to 25
 5  26 to 36

The SLC80 is a rating only, by which in conjunction with the information contained in the Australian/New Zealand Standard AS/NZS 1269.3:2005 Occupational Noise Management - Hearing Protector, the problems of hearing loss due to noise exposure for a given environment are addressed. A deeper understanding of the SLC80 rating or how to apply these ratings to your workplace can be obtained from the OH&S authority in your State.

 
©Paramount Safety Products 2011

All references to Australian Standards have been reproduced with permission from SAI Global under copyright Licence 0912-C043 and is exclusive to Paramount Safety Products. These standards may be purchased online at www.saiglobal.com. The granting by SAI Global of a licence to reproduce is in no way represented as approval from SAI Global of any alterations, additions or deletions.