PPE FAQ: Hearing Protection from the JSP Knowledge Base:
What does SNR stand for and how do you use it?
SNR stands for Simplified Noise levelReduction (often referred to as Single Number Rating). It is a rating given to an ear defender that is subtracted from the overall sound measurement to calculate the sound pressure level at the ear when wearing this particular ear-defender.
What is HML?
A method of estimating the attenuation of hearing protection based on 3 parameters.
H = High
M = Medium
L = Low
The terms refer to the noise reduction of the chosen hearing protector at High, Medium and Low frequencies.
What does dB stand for?
Decibel – the unit of sound level and noise exposure measurement.
What do Ear defenders do?
Ear defenders basically form a physical barrier between the noise energy and the ear. By passing through the ear defender the sound loses energy, and a lower energy sound means a quieter sound.
The process of losing noise energy is called attenuation, and it is the attenuation data that should be examined whilst selecting appropriate ear defenders. This data is available for all jsp ear defenders.
Appropriate Ear Defenders, I thought one was much the same as another. Why have such a large range? Due to the huge range of noise energy levels we need a range of ear defenders to match. The aim of the ear defender is to bring the noise level to the region of 75 to 80dB(A), so a higher noise will need better attenuation than a lower energy noise. If you use an ear defender which offers too much attenuation then your staff may not be able to hear fire alarms etc. That is why JSP ear defenders offer such a wide range of performance.
What are Electronic Earmuffs and how do they work?
They are Earmuffs incorporating an electronic sound reproduction system. At low levels of noise the sound detected by a microphone on the outside of the earmuffs is relayed to a loudspeaker in the muff cup. At higher levels of impulse noise the electronic circuit cuts out, leaving the inherent attenuation of the earmuffs to provide the protection.
I know what my noise exposure is, do I need any other information?
Yes, Not only do you need to know the noise level, you really need to know the level at different frequencies.
The frequencies that the noise energy level should be measured at are: 63HZ, 125HZ, 250HZ, 500HZ, 1000HZ, 2000HZ, 4000HZ, and 8000HZ. Armed with this information and the Attenuation Chart, you can select the correct ear defender to bring the noise energy below 80dB(A) at all these frequencies.
What are the 3 action levels of noise?
In accordance with the 2006 Noise at Work Regulations The action levels are:
First Action Level
A daily personal noise exposure of 80dB(A)
Second Action Level
A daily personal noise exposure of 85dB(A)
Unit value 87dB
Peak Action Level
1st Action 135dB
Peak Action Level
2nd Action 140dB
What is Tinnitus?
Involuntary noises in the ear such as ringing, often associated with hearing loss.
Explain the difference between 80 and 83dB’s?
The decibel scale is logarithmic ratio between any two sound levels. The addition or subtraction of decibels is different from normal linear calculations. Adding 3dB’s to an existing noise level doubles it, subtracting 3dB’s from an existing noise level halves it. In other words, adding two noise levels of 80dB does not give a noise level of 160dB. It gives a level of 83dB, i.e twice the 80dB noise level.
I need to wear ear defenders and a safety helmet at the same time. How can I meet both these requirements?
JSP produce a range of helmet mounted ear defender specifically designed to be worn with industrial safety helmets. The ear defenders use the Surefit™ system or the international slot adaptor to attach to our range of industrial safety helmets.
Do ear defenders have a ‘working life’?
No, A well maintained set of JSP ear defenders could last indefinitely. Some parts of the ear defender are replaceable such as the pads and foams.
The ear defenders should be regularly inspected to ensure that the cups andheadband are not cracked or split. If this is the case the complete ear defender should be replaced.
How do you test ear-defenders to ensure that they are suitable for use? JSP ear defenders are made in batches. From each batch we will take samples for testing. The first test involves measuring the headband force and the area of the ear pads to ensure that we do not apply too much pressure to the wearer’s head.
Then we carry out an Insertion Loss test which involves measuring sound levels at various frequencies with and without the ear defender over the microphone. These figures are similar to attenuation figures but are slightly different because we use artificial methods of measuring sound and not the human ear.
The ear defenders are then dropped and placed on a steel vibrator plate for three hours, this ensures that all components are securely attached.
Then we flex the headband 1000 times and then the headband is placed in a water bath at +50°c for 24 hours.
We do the insertion and headband force test again to ensure that after all the physical tests that the performance has not altered outside set limits.
Information kindly provided with permission from JSP Knowledge Base – JSP