Vibration, the Law and Trigger Time

Vibration, the Law and Trigger Time

Vibration Exposure and the Law

Regular use of vibrating equipment can lead to two forms of ill health, Carpal Tunnel Syndrome (CTS) and Hand Arm Vibration Syndrome (HAVS). Symptoms of these conditions include:

·        Hand Arm Vibration Syndrome: Tingling, numbness, pain and blanching (whitening) of the fingers and loss of strength in the hands.

·        Carpel Tunnel Syndrome: tingling, numbness, pain and weakness in the hand which can interfere with work and everyday tasks.

These conditions are preventable, but once the damage done, they are permanent; with regards to HAVS in particular currently nearly 2 million people are thought to be at risk of this condition. The Vibration at Work Regulations 2005 were introduced and require employers to control vibration, provide information, instruction and training to employees on the risk and the actions being taken to control risk; and provide suitable health surveillance.


Employers are required to assess who is at risk of vibration exposure and to what degree. The vibration risk assessment, which is part of the annual health surveillance, must estimate to what level operatives are exposed to vibration and deem whether this is acceptable compared to current guidelines. Currently, the exposure action value (EAV), the level at which measures must be taken to reduce exposure, is a daily EAV of 2.5 m/s²; the exposure limit value (ELV), the level at which operatives should not be exposed, is 5 m/s² daily.

Hand Arm Vibration Syndrome or Vibration White Finger causes whitening of the fingers and a number of symptoms which can reduce our ability to perform tasks.

How to Record Exposure

To assess our exposure, we must calculate the time spent gripping a piece of vibrating equipment. It is important to note, that this does not mean the time that the equipment was used for, but more the actual time spent gripping the equipment while it is vibrating; this is known as “Trigger time”.  There is no duty within the regulations to calculate the exact level of exposure, however, an accurate as possible estimate should be obtained to best identify those who are at risk.


To estimate trigger time, it is a good idea to measure how long you use the equipment for a given period of time and estimate the total over a shift from this number. For example, trigger time could be measured over half an hour and then the result could then be used to estimate the trigger time for the whole 8-hour shift. Alternatively, where the work task is repetitive, e.g. drilling large numbers of holes, you could measure the trigger time when drilling several holes and multiply the average by the number of holes typically drilled in a shift. This should then be recorded on a timetable as soon as the shift/task is completed to ensure as accurate results as possible are recorded. If you are using more than one tool or work process during a typical day, trigger time should be collected for each process.

As is shown in this graph (Source: Industrial Injuries Disablement Benefit) since the Vibration at Work Regulations 2005 were implemented there has been a general reduction of claims from both HAVS and CTS. This possibly provides evidence that monitoring exposure to vibration can help protect workers from its associated dangers. Recording your trigger time as accurately as possible increases the likelihood you will be correctly identified as at risk of HAVS or CTS.

(All information is correct as of 1st May 2019)