Category: News

SOUND CONTROL ADVICE

Understanding A-C-Z noise frequency weightings

What are the different frequency weightings and why do you need to know?
Understanding the difference between A-C-Z noise frequency weightings is one of the most important things you need to know about when measuring sound. This is because picking the wrong sound level meter weighting on your sound level pressure meter could mean your results become irrelevant for the purpose and at worst invalid (not legally compliant).
You may have noticed that some sound meters allow you to choose the frequency weighting you want to measure noise at. The three most commonly used decibel weightings are ‘A’, ‘C’ and ‘Z’ as defined in the sound level meter standards IEC 61672:2013 (BS EN 61672-1:2013), but which one do you choose? We explain this is more detail below, but if you own one of our Pulsar Nova sound level meters which measures all of these frequencies simultaneously, you need not ever worry about picking the wrong weighting.

What are ‘A’, ‘C’ and ‘Z’ weightings

Frequency (Hz)	63	125	250	500	1k	2k
A-weighting (dB)	–26.2	–16.1	–8.6	–3.2	0	1.2
C-weighting (dB)	–0.8	–0.2	0	0	0	-0.2
Z-weighting (dB)	0	0	0	0	0	0

Why do I need to know this?

The human ear is most sensitive to sound frequencies between 500 Hz and 6 kHz. When measuring sound pressure level variations, especially for potentially damaging noise levels for workplace noise, it is important that the sound level meter is able to give an accurate representation of what the human ear actually hears. Frequency weightings do this by giving more weight to different frequencies over others (i.e. emphasising some frequencies and de-emphasising others).

A-weighting for noise at work

When measuring the impact of noise at work on hearing the A-weighted noise measurements should be presented (commonly displayed as dB(A), (correctly written as LAeq)). Representative ‘A’ weighted average noise level readings should be taken for each task undertaken by an employee and then using software or the HSE’s calculator determine an individual’s exposure level.

C-weighted decibels for noise at work

People often forget the need to assess the risk from any impulsive noise (very sudden short-lived noises, bangs and crashes). The C-weighting is used for this to give us the peak sound pressure for the impulsive noise that the human ear is exposed to dB(C) (or LCPeak).

Most modern sound level meters and dosimeters will measure both the LAeq and the LCpeak simultaneously.

Find your perfect noise measurement equipment

• Sound level meters
• Noise dosemeters

Low hand or body temperature can increase the risks of Hand Arm Vibration Syndrome (HAVS) symptoms occurring including finger blanching and damage because of reduced blood circulation. One of the key ways of preventing hand arm vibration syndrome then is to keep hands warm for workers who are exposed to vibration, and especially for those who may be more vulnerable to complications from poor circulation such as diabetics and those with existing Reynaud’s Disease.  Here are 8 top tips for keeping warm to help prevent HAVS.

8 top tips for Hand Arm Vibration Syndrome Prevention

1. Stay warm, don’t get warm. It is a lot less work to keep fingers warm compared with getting already-cold fingers warm. So focus on employees starting out warm and staying warm with the help of a good pair of quality gloves. More than one set may be needed for employees if gloves or clothing are likely to become wet (see below). Gloves need to be a good fit and effective in keeping hands warm and dry. They should be selected to ensure that they not not stop employees working safely and do not present a risk of entanglement in machinery.
2. Stay dry. Wet hands are cold hands, so you need to keep your hands dry. Provide waterproof gloves to keep moisture from getting in from the outside, but be mindful of overheating and getting sweaty; a layering system consisting of lightweight or mid-weight liner gloves worn under a warm, waterproof shell gives you the option to wear only the liner gloves when you’re hot and pull the outer shells on when you cool down.
3. Block the wind. A waterproof glove, (as above), is naturally windproof, and protecting hands from icy winds will help keep them warm.
4. Take care of your core. When your fingers are cold, it’s natural to focus on what you’re wearing on your hands. But by wearing layers and keeping your core warm you’ll be able to pump heat out to your extremities, like fingers and toes. Providing hot drinks and warm food can also help maintain a good core temperature.
5. Avoid tight clothing. Watch straps, tight cuffs or gloves or mittens with wristbands can cause poor circulation and result in really chilly hands.
6. Watch your grip! Hands stuck in a gripped position for a long-time can make it tougher for blood to reach them. Exercise your fingers and arms with simple moves every now and again, such as wiggling your fingers and making arm circles to improve circulation.
7. Add heat. Hand warmer packets can be a great way to warm fingers, especially for people who are already prone to cold fingers or who have poor circulation.
8. Keep work places warm and dry. Cold breezes and damp environments can make it difficult to stay warm. Likewise providing screening or shelter for outdoor workers in cold, wet or windy conditions will help.

Other measures to prevent Hand Arm Vibration Syndrome

• Know your numbers. Use a hand-arm vibration meter, like the Pulsar vB, to understand how long a worker can use a power tool without being at risk of damage to their hands and nerves.
• GIVE UP SMOKING! We all know smoking is bad for us in many ways, but in particular relation to Hand-Arm Vibration, it is a proven cause of poor circulation to the extremities of our bodies including fingers and toes and can increase the likelihood of getting HAVS.
• Reduce the duration of exposure so that employees can take regular breaks from prolonged exposure with built-in recovery periods.
• Buy smooth. Make good purchasing decisions for low-vibrating tools.
• Change work processes to help design out the need to us vibrating power tools where possible.
• Keep tools and work equipment in a good working order to prevent high vibration levels and inefficient operation from poorly maintained equipment.
• Provide training in the proper use of tools. For instance, such training might cover the position of the hand on tools, the grip strength required to operate safely and ergonomic factors from the operators posture.

Noise-Induced Hearing Loss (NIHL) is one of the most prevalent, but often ignored, risks in the workplace. 

It’s important that companies comply with their legal duties in their respective regulations. These regulations reduced the previous action levels and introduced legal limits for daily noise exposure.

This blog provides a simple 5-step process for those companies who are making efforts to control the noise within their workplace.

Step 1

The first thing you need to do is establish whether there are any noise hazards within your workplace. This can be achieved through a combination of your knowledge of work practices, making straightforward observations and taking some simple noise measurements in areas that you may suspect may present a risk.

Even at this stage of the process, we recommend that you use an acoustic calibrator to calibrate your sound level meter before and after each measurement session and keep a record of your measurements.

Step 2

Once you’ve found out which areas within your workplace may be a noise hazard, you need to identify which employees could be at risk of noise-induced hearing loss.

You should evaluate how harm may occur, for instance, damage to hearing, deafness, tinnitus, impaired communication and an inability to hear audible alarms.

We recommend that you also take into consideration susceptible employees or those that already have an existing hearing condition.

Step 3

A more detailed series of individual noise measurements are required to determine the typical exposures of those at risk, so you should talk with your employees to fully understand their typical work routine. You then have a choice of measurement methods.

            Option 1: Integrating Averaging Sound Level Meter

The person carrying out your workplace measurements should be competent and should use a suitable sound level meter. Ideally, this meter should be compliant to BS EN 61672-1:2003 Class 1 or Class 2 and be from a reputable manufacturer.

Representative ‘A’ weighted average noise level readings (LAeq) are to be taken for each ‘task’ undertaken by an employee and then you should determine an individual’s exposure level by using software, mathematical formulae or the HSE exposure calculator.

The ‘A’ frequency filter is applied by sound measurement instruments in an attempt to replicate the response of the human ear to noise so that we can accurately determine the level of risk rather than the actual true noise level itself.

            Option 2: Personal Noise Dosemeter

Alternatively, a noise dosemeter can be worn by a worker during their entire shift, which will monitor and measure the noise levels they’re exposed to throughout their specific working day.

Noise Dosimetry is particularly effective for workers with unpredictable shift patterns, those constantly on the move, or people working in confined or difficult to access areas.

Having made and evaluated your measurements, a Noise Control Action Plan is required. This plan is the most important part of the whole survey process and should demonstrate that you’re taking the necessary steps to control the identified risks.

Often forgotten is the necessity to assess the risk from any impulsive noise. The action levels for impulsive noise are 135dB(C) and 136dB(C) with the legal limit being 140dB(C).

Any plan you make should include a list of prioritised actions to solve immediate risks and to give consideration to your general duty to reduce noise levels in the workplace. Where noise can’t be reduced at source, suitable hearing protection is required which must be made available to all workers at risk.

Employees should be provided with information, instruction and training with respect to the risks and how to minimise and control them.

Step 4

All of the findings from the above should be used to create a clear report which should be in a style and format that could be easily referenced in future. This will provide permanent evidence of the decisions you have taken have to comply with the law.

Step 5

You should regularly review the effectiveness of your programme for controlling workplace noise. This will be especially necessary if new equipment has been introduced or there have been changes to the layout of your factory or working hours for your employees.