HAV management
October 1st 2003 Hand-Arm Vibration is to become an increasingly prominent issue for many companies as a result of the new Physical Agents (Vibration) Directive. The forthcoming regulations based on the directive substantially increases the pressure to take action to reduce the risks associated with both Hand-Arm Vibration (HAV) and Whole Body Vibration (WBV). Unfortunately, there are particular problems associated with HAV management due to the lack of any effective protective equipment, the inherent difficulties in making reliable vibration measurements and the lack of useful manufacturers data. This article by Peter Wilson of the Industrial Noise and Vibration Centre provides a summary of the practical implications of the new requirements and a guide to effective HAV management.
The New Regulations
The EC issued the Physical Agents (Vibration) Directive on 6 July 2002. This specifies the minimum health and safety requirements with respect to the risks arising from hand-arm and whole body vibration. Member States have three years from this date to introduce legislation that implements the requirements of the directive.
The current HSE action level is set at a highest axis daily (8 hour) dose of 2.8 m/s 2 A(8) or a vector sum daily dose of 4 m/s 2 A(8). The new Directive reduces the action level to a vector sum daily dose of
2.5 m/s 2 A(8) and disposes of the highest axis value i.e. all risk assessments must be based on the true overall vibration level. It also introduces a vector sum exposure limit value daily dose of 5 m/s 2 A(8) which must not be
exceeded (a weekly average derogation may be granted where vibration exposures varies substantially from day to day).
The risk management requirements do not differ greatly from those currently recommended as best practice, but the new exposure limit value represents a substantial change that will be very difficult (if not impossible) to meet with current technology for some processes. The chart above summarises the main changes in HAV requirements under the new Directive.
Productivity Implications
As far greater numbers of operators will be exposed above the new, Lower Action Level, HAV risk management programmes will need to be substantially extended. Based on statistics derived from over 1000 field vibration measurements on the INVC HAV database, the percentage of tools that exceed the current Action Level after 2 hours use will rise from 48% to 67% (new Action Level).
In addition, 37% of the tools would exceed the Exposure Limit Value after 2 hours use. This data provides a graphic illustration of the importance of planning ahead to try to replace high vibration tools (bought or hired) with better designed, low vibration alternatives.
Effective HAV management
Hand-Arm Vibration offers a minefield of opportunities for implementing less than effective risk management strategies based on misinformation and myth. The following is a review of some of the key issues.
PPE: Anti-Vibration Gloves
This is a very simple topic. There is no generally effective PPE for vibration. So called "anti-vibration" gloves usually have little or no effect on weighted levels of hand vibration except under unusual circumstances. While gloves are useful to keep hands warm and provide physical protection, AV gloves are unwieldy, expensive and could actually make the situation worse by requiring increased
grip forces. Use conventional gloves to keep hands warm and to provide mechanical
protection. If you are considering the use of AV
gloves, it is necessary to carry out a detailed
frequency analysis of the vibration of each type of tool and then calculate the likely protection that would be afforded.
Effective Risk Assessment
Accurate HAV assessment is both difficult and time consuming compared with noise measurements (for example) and are therefore expensive. Moreover, there is normally a significant variation in the results caused by factors such as different operators, varying tool condition, materials used etc. Consequently, it is more realistic to quote a range of typical vibration values for a particular tool and activity. Best Practice involves a minimum number of measurements combined with reliable published field data from, for example, the INVC database (this is the largest database of HAV field values in Europe). This approach not only reduces costs by an order of magnitude, but it also frees resources that can be used to reduce the risks.
Field Measurements
Ensure that the assessor is fully competent and check that the correct procedure is followed. In principle, an accelerometer is rigidly attached to the tool handle and oriented in turn along each of the three axes of vibration (or a tri-axial accelerometer is used). The output is then frequency weighted in the meter (similar to the A-weighting filter in noise meters). The vector sum addition of all three axes gives a single overall weighted value for the vibration applied to the hand that is indicative of the risks of HAVS (BS EN ISO 5349). Many assessments have been made using transducers that were attached with hand-held fixtures. This gives the wrong answers. Except under very exceptional circumstances, the transducer must be rigidly attached to the tool or workpiece to give the correct value. Unfortunately, the differences are often very large, eg for a typical impulsive hand tool the safe working time calculated from results obtained using a hand-held transducer is 12.5 hours while the correct result using a hard mounted transducer is 46 minutes, an error of x16. Consequently, results based on hand held transducer readings are not acceptable in risk assessments.
Manufacturers and Suppliers Data
In order to comply with the CE marking requirements, manufacturers carry out vibration tests to BS EN ISO 8662. This stipulates a series of tests using artificial loads that generate results that are the Declared Values for the tools. This manufacturers data usually bears no relationship to real use exposure levels. For example, a chipper with a lab vibration value of <2.5m/s^2 had a measured field vibration value of 17m/s^2 . This translates to a maximum working time before the new action level is reached of 8 hours based on the lab data, whereas the actual safe working time using the field data is 0.17 hours.
Hiring/Buying Low Vibration Plant
Replacing older, high vibration machines with modern, low
vibration alternatives (where possible) is one of the most effective long term risk management measures a company can take to reduce the hazards and costs associated with Hand-Arm Vibration. As suppliers are gradually bringing out new low vibration designs, buyers, project and specifying engineers of potentially hazardous
plant should implement a field vibration data based purchasing
and hiring policy. However, as manufacturers are very reluctant to stray beyond laboratory based test results, their data is totally inadequate as the basis for the selection of low vibration
plant unless it has been independently tested under real
production conditions. Similarly, most hire companies usually
provide only the manufacturers data in the form of the
declared values.
Consequently, in order to buy or hire low vibration plant, it is usually necessary to obtain your own data directly either via independent assessments of the comparative levels of vibration from different types of plant on real activities or using published database field values as a guide. You should also assess productivity - there is little point in acquiring a low vibration tool that extends the time required to complete a job so much that the overall operator dose is greater than for a faster, higher vibration tool. Additional factors such as ergonomics and any potential operational or engineering vibration control measures are also important. This approach allows you to prove that the best new tools currently available have been selected for purchase or hire.
Maintenance
A vibration based maintenance programme is also an
important element in the risk management programme. While
some plant may still work reasonably well when in need of maintenance, the HAV risks may well be substantially increased. A system should be implemented to encourage operators to report unusually high levels of tool vibration as a prelude to maintenance.
In some cases, vibration measurements can be used to diagnose the mechanical condition of tool components prior to maintenance to ensure that the maintenance procedure itself returns each tool
to its lowest vibration condition to minimise the risk to the operator. More articles from Industrial Noise & Vibration Centre Ltd: |
