Hand Arm Vibration
HAV ratings are increasingly becoming a factor in choosing the right cutting or compacting equipment. Hand arm vibration refers to the buzz that travels from the machine through the handle to the user’s hand. In mild cases this can lead to discomfort, but there have been cases of Vibration White Finger and Carpal Tunnel Syndrome from extended exposure to vibrating equipment. For this reason, manufacturers have been putting extra efforts into reducing the HAV ratings of machinery.
In 2005 the government introduced an Exposure Action Value Limit (EAV), which requires the workplace to monitor and manage exposure to HAV levels above 2.5m/s². In practice, this would mean limiting the amount of time a worker uses such equipment, and offering aids such as gloves and foam handle dampeners.
The Exposure Limit Value (ELV) of 5.02m/s² is the maximum level a worker should be exposed to in a working day. As well as vibration levels expressed as metres per square second, every machine should have a ‘trigger time’, which is the amount of time taken to reach the EAV or ELV limits.
How to calculate safe usage times
Altrad Belle, who manufacture compaction equipment such as trench rammers and hydraulic breakers, have a long history of monitoring, research and innovation in order to reduce vibration levels on their equipment.
Belle's Compact 350X floor saw has a listed EAV trigger time of 6 hours and 31 minutes, which is basically the amount of use before the Exposure Action Value of 2.5m/s² is reached. The trigger time to reach the Exposure Limit Value on that machine is over 24 hours.
If you already have the HAV rating then you can convert this into points, which effectively would translate to a usage time limit.
|Vibration level (m/s²)||3||4||5||6||7||10||12||15|
|Points per hour||20||30||50||70||100||200||300||450|
Exposure Action Value (EAV): 100 points per day
Exposure Limit Value (ELV): 400 points per day
For example, a plate compactor with HAV rating of 3.0 could be operated by the same user for 5 hours before work rotation measures must be taken. The overall limit value would therefore be approximately 20 hours. This of course is unlikely to occur during a normal working day for one operator.
How to reduce exposure to HAV
There are two areas that can reduce the exposure to hand arm vibrations from heavy duty machinery such as sawing, breaking and compaction equipment. One is simply to limit the amount of time a worker can use a machine, but the other is to reduce how much vibration is emitted from the machines themselves.
Manufacturers of construction equipment have used various methods to dampen the vibration levels of compaction and cutting equipment such as adding foam to the handle, or relocating the moving parts in relation to the handle. Certain materials and grades of metal will transfer lower levels of vibration, and typically the more distance between the impact point and the handle(s), the lower the HAV levels.
The key point at which HAV is experienced and measured is in the handle, or wherever the hand comes in contact with the machine. A recent innovation for plate compactors has come from Atlas Copco’s compaction division, now operated by Husqvarna. Special vibration dampening handles on forward compaction plates are ergonomically designed and strategically placed so that there is minimal travel of the vibrations from the main frame. The result is a level of vibration below 2.0m/s², thus allowing for a full day of use without excessive risk of injury.