How to Calculate HAV Exposure: Using Vibration Exposure Points

If you want to manage and control Hand Arm Vibration risk then measuring an individual’s vibration exposure is a must. In this article we look at how to use the vibration exposure points system to do this. 

Why Do You Need to Measure Hand-Arm Vibration?

The key reason for measuring vibration is to reduce the risks of your employees developing hand-arm vibration syndrome (HAVS). You should use a hand-arm vibration meter to measure the vibration magnitude of tools if: 

• Suitable vibration data is not readily available
• You are unable to make a reasonable estimate of the vibration exposure level and you can’t say with any confidence whether the Exposure Action Value (EAV) has been exceeded or not.
• You need reassurance that the data you have used is accurate
• You need measurements to confirm whether any control measures you have put in place are successful
• You need your own measurements to give you data with which to fight personal claims.

Vibration assessments apply to companies large and small, and the HSE in the UK recommends that even companies with less than 5 employees should record any Hand-Arm Vibration findings, even if the levels are low, and review their assessments. 

Why You Should Not Rely Solely on Manufacturers’ Vibration Data

Whilst manufacturer’s data can be useful in comparing one tool with another, especially for ‘buy smooth’ procurement decisions, when carrying out a vibration assessment, it is vital to collect your own vibration data for each piece of equipment used and for each kind of task it is used for. You cannot simply rely on manufacturers’ data; this is because the tools are used in ‘favourable’ factory conditions and how you use the tool, or its age or level of maintenance, could be completely different.  As alternatives to using manufacturers’ data, the HSE provides a table of expected levels of vibration from different tools which can be used as an initial assessment – but not in the full risk assessments.

If the tool you are measuring has two handles, for instance on some strimmers or chainsaws, you should measure vibration from both (as there are two places for the operator to receive vibration), but always take the higher value when assessing exposure.

What Should Be Measured in a HAV Risk Assessment?

You measure the potential a power tool, for instance, has to damage someone. The operation of a power tool is measured using a handheld vibration meter; this tells you the total vibration (Vector Sum) of the tool along three axis X, Y, Z (into the palm, across the knuckles, and up the arm) of the person using the tool. From here, you can use the software provided with the meter, or the HSEs calculator, to work out the potential hand-arm vibration exposure from the tool, and how long an employee can use it for before they are at risk of damage.

What Is A(8) Vibration Exposure?

A(8) represents daily vibration exposure normalised to an 8-hour reference period. Normalising exposure allows vibration levels measured over shorter periods to be compared consistently against legal thresholds. A(8) is used to determine whether the Exposure Action Value (EAV) or Exposure Limit Value (ELV) has been reached.

Exposure Action Value (EAV) and Exposure Limit Value (ELV)

The hand-arm vibration exposure levels set out in the Control of Vibration at Work Regulations 2005 are: 

The limit value must never be exceeded in a workers day, and employers should aim to reduce levels of vibration to ‘As Low a level As is Reasonably Practicable’ (ALARP) – at the very least the aim should be to be below the EAV (below 100 points).

Calculating HAVS Exposure

The most accurate way to calculate an employee’s exposure to HAVS is to use a hand-arm vibration meter, sometimes called a HAVS meter. Using this you can calculate the vector sum of the power tool which will enable you to use vibration exposure points or tool timers to calculate an employee’s exact daily exposure.

Using Vibration Exposure Points

The action value of 100 points is made up of all the trigger times from all the tools used by a worker in their job on any given working day. Assessing points per hour or per 15 mins trigger time seems to work well for most tools. It is much simpler to add the points up and use a Ready Reckoner (based on the HSE’s) to identify overall vibration exposure than to add the vibration magnitude (A(8) Vector Sum data) of individual tools. On the Ready Reckoner, the exposures for different combinations of vibration magnitude and exposure time are given in exposure points instead of values in m/s2 A(8). Note that:

• Exposure points change simply with time: twice the exposure time, twice the number of points;
• Exposure points can be added together, for example where a worker is exposed to two or more different sources of vibration in a day;
• The EAV (2.5 m/s2 A(8)) is equal to 100 points;
• The ELV (5 m/s2 A(8)) is equal to 400 points;

Vibration Tool Timers

The use of vibration tool timers can significantly improve the way in which you monitor your employee’s exposure to vibration. To ensure maximum accuracy, you need to pair these timers with a fully calibrated vibration meter in order to get the correct vibration magnitude. Once this is done, you can then input this value into the tool timer, and it will automatically calculate your vibration exposure points.

Ensuring that you monitor these exposure levels enables you to rotate employees’ tasks depending on their exposure level for the day. For example, if you have an employee who is using a jackhammer, they will need to be rotated onto a task that doesn’t involve power tools or high vibration levels to avoid them exceeding the 100-point Exposure Action Value(EAV), ideally.

Controlling and Reducing HAV Exposure

A total exposure of 100 points or more indicates increased risk, and administrative or engineering controls should be considered.

A total exposure of 400 points or more indicates that safe limits have been exceeded and immediate action is required.

Control measures should be introduced whenever exposure is likely to reach or exceed the EAV. Effective control measures may include:

• Using a calibrated hand-arm vibration meter to carry out risk assessments
• Setting usage limits for high-vibration tools
• Rotating staff to reduce exposure duration
• Ensuring tools are properly maintained
• Selecting lower vibration tools where appropriate

Limiting exposure duration should be considered only after other engineering or organisational controls have been evaluated.

Whole-Body Vibration Exposure

The discussion above equally applies as much to whole-body vibration as it does to hand-arm.

The whole-body vibration exposure levels set out in the Control of Vibration at Work Regulations 2005 are: 

The limit value must never be exceeded in a workers day, and employers should aim to reduce levels of vibration to ‘As Low a level As is Reasonably Practicable’ (ALARP) – at the very least the aim should be to be below the EAV (below 100 points).