9th September, 2015
The Control of Vibration at Work Regulations enforce two exposure values for vibration at work, one of which, the Exposure Limit Value, must not be exceeded. But how do we calculate our vibration exposure at work?
The Control of Vibration at Work Regulations were introduced with the purpose of making sure that workers did not suffer ill health due to exposure to vibration at work.
The regulations set an exposure limit value (ELV) of 5m/s²A(8), which must not be exceeded.
Does this mean, that if a tool has a vibration output of 10m/s² it cannot be used as it exceeds 5m/s²?
After all, employers must not allow exposures to exceed the ELV.
Well, actually the A(8) part of the ELV is important, it means average over 8 hours. The 10m/s² tool can 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 life 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!).
Don't despair, once you get your head around the maths you will know exactly 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 used by the HSE to help calculate exposure.
In this example 400 points are the same as our ELV of 5m/s²A(8).
All you need to remember is, 400 points is your maximum exposure, and it can't be exceeded each day.
Now, we need to give each tool a number of points per hour. This 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 looks simpler written like this...
(Output x Output) x 2 = Points
Ok, let's look at our 10m/s² tool.
(10 x 10) x 2 = 200
So thats 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 how long we can use the tool for.
400 / 200 = 2
2 hours. Once this time is up, you have used up all your vibration points, and you can't be exposed to any more vibration that day, 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 brands latest model, and it gives 7.5m/s².
How long could this tool be used for 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 your 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 amount of minutes. In this case 33 (ignore the decimals to work in whole minutes).
Phew, if you followed this post all the way 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.