If powered tools are extensively used in your organisation and you think employees are potentially at risk of injury to their fingers, hands and arms, known as HAVS, then you are obliged to carry out a HAV risk assessment. This exercise will require you to get a good estimate of the operative’s daily exposure known as the A(8) value, and there’s a very useful online HSE spreadsheet which may be used for this purpose.

The A(8) value can then be compared against the exposure action & limit values as stated in the Control of Vibration at Work Regulations (2005), and if there is an issue, risk controls may be applied accordingly. The spreadsheet is also capable of predicting the maximum allowable tool trigger (usage) times before hitting the exposure action and limit values.

What if you find yourself in a position where you are not within easy access of the HSE spreadsheet and wish to estimate A(8), or indeed the maximum allowable trigger times for a tool? You may be on your shop floor or out in the field carrying out vibration level measurements where it’s not so convenient to return to your desk.

Don’t despair. All you need is a calculator (your smartphone should have one) and to apply the following simple equation (it’s stated in the regulations and worth memorising):

**VEP per hour = 2v ^{2}**

Where, VEP = the HSE vibration exposure points

And, v = tool vibration level (in m/s^{2}) [this value may be obtained through measurement, from manufacturer’s data, or from a reliable database].

You should also be familiar with working in terms of VEPs, where A(8) = 100 VEP equates to the action value, and A(8) = 400 VEP equates to the limit value.

To estimate A(8),

- Start off by inserting a value for v into the equation, to obtain the VEP per hour.
- Next, multiply the VEP per hour by the trigger time (expressed in hours) provided by the operative, to predict the VEP for the particular tool.
- For multiple tool use daily, simply sum up the VEP for each tool to predict the overall A(8).

Refer to the worked example below, where 2 tools, A and B, are used on a daily basis by an employee:

Tool |
Vibration level, v (m/s^{2}) |
VEP per hour [=2v^{2}] |
Daily Trigger time (hours) |
VEP [=VEP per hour x Daily trigger time] |

A |
4.5 | 41 | 2 | 82 |

B |
6.7 | 90 | 1½ |
135 |

A(8) |
217 |

The exposure action value (100 VEPs) has therefore been exceeded (A(8) = 217 VEP). As a result, there are specific obligations to fulfil in accordance with the regulations when reaching the exposure action value.

It is also possible to predict the trigger times taken to reach both the exposure action and limit values for any tool. These are mathematically expressed as 100/(VEP per hour) and 400/(VEP per hour) respectively.

So for tool A in the above table, the trigger times taken to reach the exposure action and exposure limit values would be given by 100/41 (= 2 hours 26 minutes) and 400/41 (= 9 hours 45 minutes), respectively.

Like wise for tool B, the trigger times taken to reach the exposure action and exposure limit values would be given by 100/90 (= 1 hour 6 minutes), and 400/90 (= 4 hours 24 minutes) respectively.

This equation is simple, but powerful, and allows you to use an alternative and convenient method to determine the daily exposure (plus allowable tool trigger times) if the HSE spreadsheet is not easily accessible. It’s an equation that’s worth memorising.

A free guide to conducting a hand arm vibration (HAV) risk assessment is available for download. It explains, amongst other things, when you should carry one out, and what constitutes a competent risk assessment. Click **here** to receive it.