In this post you'll learn
According to the US Occupational Safety and Health Administration (OHSA), Hand-Arm Vibration (HAV) is a vibration exposure that mainly affects people who regularly use vibrating pneumatic, electric, hydraulic, and gasoline-powered hand tools. Research and studies going back to 1918 link HAV exposure to a condition of the fingers and hands called Hand-Arm Vibration Syndrome (HAVS). Typical signs are loss of sensation in fingers such as tingling, or numbness followed by a white or blue finger due to loss of blood circulation. These symptoms indicate nerve and vascular damage is occurring and although they might only appear in cold weather initially, with continued exposure the condition becomes more severe and can occur at any time.
They suggest that:
“Presently, most doctors and scientists have found HAVS to be generally irreversible. Workers experiencing HAVS signs and symptoms are advised to stop all vibration exposure and seek medical attention immediately.”
Assessing and Quantifying Vibration
As the vibration generated using a variety of tools in a myriad of applications creates a huge range of effects experienced by the user this effect must be measured, then assessed before comparing against limits for tool use.
Vibration is measured by a formula known as an A(8) value which is the total vibration value.
This is the average (A) exposure over an eight-hour (8) day and considers the magnitude of the vibration and how long you are exposed to it. The A (8) value is calculated in metres/s² as the acceleration that the operator experiences when using a particular tool for a length of time.
As the magnitude of the vibration varies for every tool and application it needs to be considered as the acceleration experienced simultaneously in three perpendicular axes to give a comparable, realistic value. The acceleration of the tool and therefore the operator’s hand is measured in the x, y, and z axes to give the total effect on the user.
Tri-axial accelerometers, where 3 accelerometers are in one package, will be labeled to indicate the x, y, and z axes of the device. When rigidly mounted on a tool, the x-axis needs to point through the back of the hand, the y-axis across the knuckles of the hand, and the z-axis run parallel to the plane created by the bones in the back of the hand. However, these measurements taken “on the bench” can only measure the output of the tool at the manufacturer’s site, they are not application-specific where further variations occur.
Many hand tool providers and OHS online advise visiting the UK Health & Safety Executive website for information on vibration (See Resources below). This site provides advice and information on Hand Arm Vibration (HAV) and it includes an HAV Exposure Calculator that is easy to use to work out the daily vibration exposure for tool users.
The table given at https://www.hse.gov.uk/vibration/hav/source-vibration-magnitude-app3.pdf from the UK Health and Safety Executive shows the typical range of vibration for a variety of tool types.
- Chipping hammer Hitachi Electric (1.3Kw) ISO 8662 12
- Wall chaser Bosch Electric (0.9Kw) ISO 8662 4
- Hammer drill Hitachi Battery ISO 8662 6.5
- Hand drill Makita Electric (0.23Kw) ISO 8662 <2.5
- Angle grinder Hitachi Electric (2Kw) ISO 8662 <2
In the UK the Control of Vibration at Work Regulations 2005, based on the European Physical Agents (Vibration) Directive (2002/44/EC), specify daily exposure limits. The first threshold is known as the Exposure Action Value (EAV) specified as 2.5 m/s² A (8) at which employers will be required to take action to control risks. The regulations also dictate an Exposure Limit Values (ELV) of 5.0 m/s² A (8) when the employer must prevent any further daily exposure.
Techonology to reduce industrial hand tools vibration
Since 2005, Metabos’ “VibraTech” anti-vibration handle has been included as standard with all angle grinders. A cushioning zone created by the large volume of elastomer material inside the handle means the operator is estimated to experience up to 60% less hand-arm vibration.
Other vibration-reducing technologies work by transferring air around a series of chambers, which causes a counterbalance to being pushed in the opposite direction of the piston. This cancels out the vibrations that would otherwise have been caused by the piston.
Some tools also feature shock-absorbing handles for extra protection. As vibrations travel down the handle, it is shifted in all directions thanks to a ball joint that functions as a fulcrum. The rubber dampeners then soak up this movement, which in turn lowers the vibration levels that are transferred to the user.
The HSE table referenced above for vibration values also shows that there has been significant improvement in vibration reduction for some tool types. For example, Needle Scalers with vibration reduction technology have reduced the vibration range from 12-26 m/s² to 3-8 m/s².
Though these new anti-vibration tools often cost a little more, they pay for themselves not only by allowing longer work periods but also prevent HAVS symptoms.
Ultra Low Vibration Scalers
An example of this tool type for scaling and chiseling is our very own Low Vibration Scalers. With a pistol grip that reduces vibration over prolonged use in tough applications, it makes light work of removing heavy coatings and corrosion. Featuring Trelawny’s unique Vibro Lo™ vibration reduction system these scalers offer unrivaled performance, reliability, and reduction in levels of harmful vibration, both as needle and chisel models.
The most effective means of reducing the likelihood of HAVS is undoubtedly reducing the amount of time spent using a particular tool. At the worksite, this can be achieved by rotating personnel that are required to use equipment producing vibrations.
Monitoring devices to measure and avoid harmful effects
There are many HAV monitoring devices that are worn like wristwatches to monitor vibrations experienced by the tool operator. The wrist device “talks” to the type of tool being used so that the total A(8) value of their exposure when using different tools is accumulated. Therefore, once the EAV is reached a visual and audible alarm warns that action to change the task or stop work altogether needs to be taken. One such company, HAVI, recommends task assessment using their devices rather than continuous monitoring of every tool user. As experience with various tools is gained over a variety of applications then only the workers performing the riskiest tasks need to wear HAV monitoring devices all day.
Conclusions on international efforts to reduce HAVS
In conclusion, UK and European regulations require suppliers to provide comparable information on the vibration emission value of their equipment in the form of an A(8) value. Therefore, for this geographic region, any estimates of vibration level would need to be verifiably quantified rather than the vibration reduction estimated as some manufacturers do. Internationally there is a tendency for some national bodies to use European regulations as a standard as they are quite often the most stringent.
The means of monitoring the vibration experienced by workers, which keeps exposure within internationally recognized daily guidelines, are readily available for assessment of any task. Therefore, employers need to recognize that ignorance of vibrational effects on their workforce is not a valid excuse.