Measuring noise - I heard it through the...

Ian Mitchell, a former Senior Training Technician at Cutting Edge Training, now runs his own training company. In this article for his former employers, he discusses the issue of noise - how it's measured and its effect on operators working with outdoor power equipment

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For many workers in factories and wider industrial work sites, background noise levels are part of the environment they work in. The risk to hearing damage is easily assessed by taking sound readings. Appropriate hearing protection can easily be issued and audits taken to ensure that the PPE issued is being worn and, more importantly, worn correctly.

For many of us who work in the groundcare and horticultural sectors, mechanical noise is a temporary problem, only generated by the machinery we are using as part of what is often a wide and varied job. Noise levels are constantly changing from very low to high, depending on the tools being used, so assessing noise exposure can be more difficult. Add to this the issue of staff working over large sites or at remote locations, and the requirement to assess correct use becomes much harder to manage.

So what are the limits?

The Control of Noise at Work Regulations 2005 define 'exposure action values' - levels of noise exposure which, if exceeded, require the employer to take specific action. There are 'lower' and 'upper' action values, the lower action value being 80dB, the upper action value at 85dB. The maximum exposure value is 87dB.

Therefore, we need to consider hearing protection at 80dB and have to act at 85dB. Nothing should exceed 87dB. So, how many of us actually measure operator noise levels, and how many just go by the warning decals on the actual equipment?

All CE approved machinery has to display the measured noise level (usually a silver/grey decal); engine powered machinery, such as ride-on mowers or brushcutters are usually between 100 and 110 decibels.

Let's look at a brushcutter or hand held hedgecutter with a two-stroke engine running at high speed. The operator is exposed to the full noise this generates. The CE decal and the operator's instruction book will quote the tested value and this will be used to work out the level of hearing protection required when using that particular piece of equipment. Therefore, it's actually pretty straightforward.

However, a ride-on mower is quite different. On a larger machine, there is much greater scope for moving the sources of noise away from the operator. The main culprit of noise generation is, of course, the engine. Air filter intakes, radiator cooling fans and the exhaust system all generate noise and all are directed away from the operator's ear. Modern designs use baffles, anti-vibration pads and non-vibrating materials to keep noise levels as low as possible.

Machines do, however, still produce noise and, whilst clever design moves the noise away from the operator's ear, this still effects the immediate area around the machine. So, the figure quoted on the silver CE decal is NOT what the operator is actually subjected to. It is the maximum noise level produced by the machine and it is usually found several metres behind it! A more accurate way of describing this reading would be the bystanders' noise level.

So on a machine like a Ransomes Parkway 3, a heavy duty triple mower, popular with councils and contractors, the sound level on the CE decal is quoted as being 105dB, but in the operator's instruction book the operator's noise level is actually 85dB!

Which, rather conveniently is the upper exposure action value for an eight hour working shift. When you take into consideration that this value is the result of the manufacturer's static test - and most operators will be mowing at an average speed of 3mph - then the actual noise at the operator's ear is likely to be lower still. If we then look at the actual operating time, it's more than likely going to be less than eight hours, especially if the machines are transported from site to site on vans or trailers during the working day.

So, why not show the operator's noise level on the machine as well? Well, in a roundabout way, we do. Remember all those bright yellow warning decals on every piece of machinery you own or operate? This particular warning decal says "READ THE OPERATOR'S INSTRUCTION BOOK" and it's fitted to almost every CE approved machine in your fleet. So, if the operator follows the warning decals on the machine, he/she will read the manual and, therefore, find the actual noise levels which affect them. Many of these symbols will also be in blue and white, making reading the instruction not only important, but mandatory!

So, there is no excuse for not knowing what noise level the operator is exposed to and select their PPE accordingly. Whenever a new piece of equipment is delivered, the supplier should install it correctly and show you/your staff where the noise level test results are in the operator's instruction book. This is a key part of the BAGMA Installation training course, which all dealer staff who install machinery should complete.
This begs the question, do you really need ear defenders to operate a machine at 85dB? And, if you do, what is the level of protection you actually need?

The only way to decide whether hearing protection is required or not is to measure the risks and assess them. Measurement should start with getting the right information from the operator's instruction book and reviewing the actual exposure times. Then an informed decision can be made. Every business should have a clear policy regarding noise hazards and many decide that ear defenders are worn at 80dB and above.

Hearing defenders: Ear defenders basically come in two types - external defenders (EN352-1) and ear plugs (EN352-2). Without the correct EN coding, they are either ear warmers or just headphones. They are not hearing defenders! Anyone using their own personal devices at work should have to prove that they are actually noise compliant.

Worn Correctly: You should never have music playing inside your ear defenders. Aside from the hearing damage you may suffer, there is the complete lack of external sound. You are basically making yourself deaf to the outside world. Approaching hazards will go unheard.

Also, the noise generated by the machine can provide valuable feedback about how hard it is working and any warning buzzers or alarms will also go unnoticed. Your concentration could be affected, making operation more dangerous. PPE is important, and it should/must be worn and used correctly.

Levels of Protection: All hearing protection is tested and should quote the level of protection it provides, either on the packaging or on a technical manual within the packaging (that's the piece of paper with the fine print thats usually thrown away!).

The protection level is quoted as the SNR (Single Number Rating). So, a pair of defenders with 30 SNR will reduce the external noise level by 30dB. Most of us get either 28 or 30 SNR defenders when they are issued by either the stores or our suppliers. These are perfect for a Brushcutter producing 110dB, as the operator's noise exposure is reduced to 80dB. However, on the Ransomes triple mower quoted earlier at 85dB (operator's ear), the final level is a whisper quiet 55dB.

Good news then? Well, not necessarily so, as over protection can be a serious issue. If there is traffic to negotiate, the general public, or perhaps children in the vicinity, then the operator may not hear these potential hazards until it is too late. The current HSE advice is to not go under 70dB, which would mean finding ear defenders rated at, or under 15 SNR, which are not readily available.

I train many operators who claim that they cannot hear what is going on around them when wearing ear defenders. Whilst this sort of comment is often just trying it on, I do believe that this is a genuine case on quieter machinery, so it is worth considering whether hearing protection is actually required and, more importantly, getting the right level of protection for the job.

Test it yourself!

A simple phone app, available as a free download, will give you a basic dB meter. Whilst it is not as sophisticated as the proper testing equipment used by professionals, it will give an accurate enough indication of the action values stated in the noise regulations.

The limit is the quality of the microphone in the phone you are using; they are designed to work on the human voice, at conversational levels (50 to 70dB), but they are still pretty accurate at 80 to 85dB. Above that, we should be wearing hearing protection anyway, and accurate figures are available in the operator's manual.

Factory Based Testing

So how do manufacturers test their machines for noise? Well, the rules are laid out under EN352 and have to be applied uniformly for each and every test. Testing has to be carried out on a flat, open area of high quality turf cut to 30mm, which is visibly free of grass clippings, debris, moisture, frost or snow.

The weather plays its part too; wind speed must not exceed 8 m/sec, the temperature has to be a minimum of 5OC and wind speed, direction, air temperature and air pressure all have to be recorded.

The test microphones are preferably connected by a cable and background noise recordings are taken prior to the machine noise test. The mower is stabilised, by running at operating speed for at least thirty minutes and the test is carried out immediately after stabilisation.

The machine must be stationary, have less than half a tank of fuel, the cutting units must be at their maximum speed and the engine must be running at full speed. If grass boxes are fitted, they must be empty. There should be no operator present.

Six microphones are used and evenly spaced around the machine, measuring the noise levels for fifteen seconds at each of the six recordings that are taken to achieve a standard deviation of repeatability, thus ensuring that each test falls within agreed parameters.

Readings are also taken at the ear level of the operator.

The measuring equipment has to be tested and calibrated every two years to ensure conformity, and best practice includes taking a current model off the production line and testing it against the original noise data on an annual basis.

Obviously, new machinery with well-balanced blades and good bearings will make less noise than an older machine which may have worn components or spurious spare parts fitted to it. However, a well maintained machine shouldn't make any more noise than a new one, so there is an added incentive to keep up on servicing and maintenance of machinery.

Conclusion

Employers should issue personal hearing protection to employees where extra protection is needed above what has been achieved using noise control; and, as a short-term measure, while other methods of controlling noise are being developed. Hearing protection should not be used as an alternative to controlling noise by technical and organisational means.

Also, employees should be issued with hearing protectors and it is the employer's responsibility to make sure they use them fully and properly when their noise exposure exceeds the upper exposure action values.

You should only use CE-marked hearing protectors and maintain them so that they work effectively. Factors that affect the level of protection, such as the headband tension and the condition of seals, should be checked as part of general maintenance procedures.

Employees have a duty to report any defects in hearing protection and should be provided with training so that they understand the risks they may be exposed to, and their duties and responsibilities.

Consulting with trade union-appointed safety representatives or other employee representatives is a legal requirement and employers must provide health surveillance for all employees who are likely to be frequently exposed above the upper exposure action values, or are at risk for any reason.