Acoustics – hearing protectors
Design and construction
The design and construction assessment is required to confirm that the device is safe for use and will not cause injury or impairment to the wearer.
It must be ensured that the materials used in the manufacture of the device, which will come into contact with the skin, are non-staining and not likely to cause skin irritation, allergic reaction or any other adverse effect on health.
The information and user manuals supplied to the wearers with the product are reviewed to ensure that they meet the specifications of the relevant AS/NZS standard.
The marking of the device and/or its packaging is inspected. This is an examination of the final product to ensure that the correct markings are present, as specified in the relevant AS/NZS Standard.
The clamping force of the device is measured using a force rig to ensure that there is no excessive force on the wearer's head.
Dry heat test
The device is subjected to dry heat for a period of 16 hours, at a temperature of 50°C and a humidity of 5%.
Low temperature drop test
Resistance to damage when dropped is evaluated by dropping the hearing protection product from a specified height onto a solid steel plate at a temperature of -6°C. Alternatively, this test can be conducted at -20°C.
In the case of ear-muffs, the headband of the device is subjected to flexing for 1000 cycles using a flexing rig.
The cleaning methods specified by the manufacturer are tested to ensure that the cleaning and disinfection methods indicated cause no damage or impairment to the hearing protection.
Change in clamping force
Once the tests above are complete, the clamping force is measured for a second time, with a maximum deviation between the two measurements providing the pass criteria.
The subjective attenuation testing uses human subjects to assess the performance of a hearing protection device, and does carry a minimum attenuation value to pass the test. The results of these tests are published with the model when it is placed on sale and supplied to wearers. This test measures the threshold of hearing – the lowest sound pressure level perceivable by the ear – of sixteen or twenty human test subjects with and without the hearing protection worn. It is then possible to calculate the performance of the model from these values.