13th April, 2021
The exposure limit value (ELV) under the Control of Vibration at Work Regulations is a value you must not exceed. But how do we calculate this limit? Calculating the ELV in real-life situations is not always straight forward, but using a points-based system, you can keep track of exposure levels.
Many people are exposed to vibration as part of their jobs, using vibrating equipment such as breakers, wacker plates, hammer drills and even lawnmowers. In the short term, you might not notice any problems with this. But regular exposure can have a devastating impact over time, as nerves, muscles and joints become damaged. Numbness, loss of strength and grip are all symptoms of hand-arm vibration syndrome (HAVS) caused by vibration. And once developed, it's effects are irreversible.
Because of this risk of damage to health, the Control of Vibration at Work Regulations enforce two exposure values for vibration at work. The exposure value we will look at in this post, the Exposure Limit Value (ELV), must not be exceeded. It is the maximum amount of vibration you can be exposed to. Anything above the ELV is breaking the law.
Of course, you shouldn't be exposed to the maximum value unnecessarily. Health and safety is all about reducing risk. Keeping risk as low as reasonably practicable (ALARP). So the regulations also enforce a lower Exposure Action Value (EAV), after which you must take action to control vibration levels.
The Control of Vibration at Work Regulations are in place to prevent workers from developing ill-health due to exposure to vibration at work. To avoid the symptoms of HAVS, it limits the amount of vibration a user can be exposed to at work.
The regulations set an exposure limit value (ELV) of 5m/s²A(8), which you must not exceed.
Let's break that down so we can understand what number and letters mean.
5 = the limit value.
m/s² = metres per second squared. This is a measure of the intensity of vibration exposure, meaning the level of vibration.
A(8) = average over 8 hours. This is a measure of the duration of vibration exposure, meaning how long you are exposed for.
But how do you calculate vibration exposure at work to know if you are exceeding the limit value?
So that you can calculate vibration exposure, you first need to know vibration levels. Every tool does not expose the user to the same levels of vibration. For example, a lawnmower will have lower vibration output than a hammer drill or a wacker plate.
There are several ways you can find out the vibration levels for the tools and equipment you use. Manufacturers of vibrating equipment will measure the vibration output and supply this information within the product information manual. You can also measure and monitor vibration exposure yourself, with devices available. These can either attach to the tool or worn by the user.
Manufacturers will often provide several values because the vibration output will vary depending on the mode, settings, and the material you are working on.
As you can see, using the same tool, the vibration output can be a massive 10m/s² difference drilling into concrete vs drilling metal.
Other things can also affect the vibration levels of the tool. Wear and tear of the equipment. The type of accessories used. The condition of the accessories and parts used.
But the ELV is 5m/s²A(8). Does this mean that if a tool has a vibration output of 10m/s² that you can't use it? As it exceeds 5m/s²? After all, employers must not allow exposures to exceed the ELV.
Well, actually, no. The A(8) part of the ELV is important here - it means averaged over 8 hours. So the 10m/s² tool can still be used, but not for a full 8 hours.
So could it be used for half the time - 4 hours? After all, it is double the ELV. No, this is not correct either! As you can see, calculating the ELV in real-world situations is not a straightforward as you might hope.
Pssst... at this point you can cheat and use our free havs calculator (we won't tell anyone!).
On the surface, calculating the ELV might seem tricky. But don't despair - once you get your head around the maths, you will know when to stop drilling, sanding, cutting, or whatever other activity it is that is exposing you to vibration at work.
One of the easiest ways is a points-based system. This system is even used by the HSE to help calculate exposure.
In this example, we use 400 points to represent our ELV of 5m/s²A(8). All you need to remember is, your maximum exposure is 400 points. Once you have used 400 points in a day, you have reached the limit.
Now we have our maximum points, we need to give each tool a points per hour rating. This rating is how many points you use up for each hour on the tool. The maths that we have to use to give our tool the correct amount of points is its vibration output squared and then doubled. It's more simple written like this...
(Output x Output) x 2 = Points
Ok, let's look at our 10m/s² tool. We multiply the vibration value by itself (10 x 10) and then double it.
(10 x 10) x 2 = 200
So that gives us 200 points per hour when using our 10m/s² tool.
We know we only have 400 points per day, so if we divide our 400 points by the points per hour, this tells us the maximum time we can use the tool for.
400 / 200 = 2
2 hours. Once this time is up, you have used up all your vibration points for the day, and you can't be exposed to any more vibration, from this or any other tool.
Ok, let's look at one more example.
In this example, we will go for an Angle Grinder. I've looked up the vibration output of a well-known brand's latest model, and it gives 7.5m/s². How long could this tool be used before reaching the ELV, which is the maximum amount of exposure legally allowed under the Control of Vibration at Work Regulations?
Why not give it a go yourself using the example above before looking at the answer below...
What did you get?
Here's the worked through maths step by step.
First we get the points per hour:
(7.5 x 7.5) x 2 = 112.5
So we use up 112.5 points for every hour on the tool.
Then we divide the total allowed points (400) by the points per hour.
400 / 112.5 = 3.5555555
So we know that after 3 and a half hours (3 hours and 33 minutes to be exact) you have reached the exposure limit value (ELV).
One last maths trick, if you're wondering how we get the 33 minutes. First, remove the 3 hours... so you just have your minute value which is 0.555555 in this example, then multiply this by 60 to get the number of minutes. In this case 33 (ignore the decimals to work in whole minutes).
Phew, if you followed this post to the end, well done! Don't forget, the other value set by the Control of Vibration at Work Regulations is the Exposure Action Value.
You might use more than one vibrating tool in a day, so don't forget that your total exposure for the day must include all vibrating tools you use. Try the free free havs calculator for an easy way to measure your exposure.
This article was written by Emma at HASpod. Emma has over 10 years experience in health and safety and BSc (Hons) Construction Management. She is NEBOSH qualified and Tech IOSH.
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