Posted on: March 1, 2017
Misunderstanding Hand Arm Vibration monitoring marketing material can put hands and safety policies at risk. Caveat emptor.
Stop Press: 27/02/17: HSE has just issued new guidance on HAV measurementand management covering similar concerns. These may well change the way you measure and monitor HAV risk – dramatically… A one-day HAV Master Class and competency update workshop covering these topics is now available. Book a place to ensure that you are up to date with best practice – places are limited.
More on the HAV Master Class workshop and a copy of the new HSE guidance
We are regularly asked about new vibration measurement technology, particularly re the latest hand-held, glove or wrist-mounted vibration transducers that are presented as the latest assessment improvements. Whilst they may be useful tools, unfortunately some claims have been disingenuous and end-users have misunderstood the limitations inherent in the vibration measurement techniques. Where these techniques do not conform to measurement standards, the results cannot be compared with the regulatory action and limit values. If these values are mistakenly used, then operator risks could be seriously underestimated. Put simply, none of these alternative measurement techniques provide values that can be used for a reliable assessment of the levels of vibration to which operators are exposed as per BS ISO 5349.
The following is a summary explaining why alternative HAV measurement techniques may not provide correct values. Click below to acquire the definitive white paper guide.
Why is poor vibration measurement technique such a recurring issue?
Correct measurement technique is a regular issue because the British Standard (BS EN ISO 5349-1:2001 2:2002) technique is time-consuming. Common problems include:-
Note: the statistics used to estimate the relationship between the level and duration of vibration (dose) and the damage risk were based on values from transducers hard-mounted to tool handles. If a new measurement method gives a different value, it is incorrect by definition. Moreover, the HSE guidance recommends spending a minimum on measurement, investing in risk reduction instead. In keeping with this recommendation, for example, most of our HAV risk assessments are taken from our extensive HAV-Base database of accurate field vibration values. This can dramatically reduce (or even eliminate) measurement via virtual assessments by email (contact us for details).
Why non-standard vibration measurement techniques are not accurate
The reasons why alternative measurement systems do not provide vibration values comparable with the regulations are down to the simple dynamics discussed below.
BSEN ISO5349-1:2001/2:2002 measurements
The standard measurement where the transducer is hard mounted to the handle. This can be modelled by a stiff spring with low damping which does not vary.
This provides the most reliable and repeatable data which can be compared directly with the regulatory action and limit values.
Hand-held or glove mounted transducer.
The transducer is gripped between hand and handle or is mounted in a glove as illustrated. This introduces a set of soft, variable springs with high damping between the handle and the accelerometer. Consequently, higher frequencies are progressively filtered out. In addition, the handle shape and grip strength can seriously affect the measured level of vibration (for a constant vibration source). It is not difficult to measure levels that are less than half the correct value.
Wrist mounted transducer
Wrist mounted “watch” based transducers are very effectively vibration isolated from the source. Only low-frequency vibration is transmitted into the accelerometer.
Consequently, the measured value can bear even less relationship to the actual vibration in the handle than for hand-held transducers.
It is also highly variable – how tight do you wear your watch-strap?
HAV tool vibration measurement – the hard (and only correct) way…
The BS ISO 5349 vibration measurement technique minimises the number of variables involved in hand-arm vibration measurements and provides the only accurate levels that can be compared with the risk statistics (the basis for the action values in the regulations). That is not to say it is not possible to devise better measurement techniques, but many years of work would be required to relate any vibration values to operator risk.
Some marketing literature surrounding the use of hand-held, glove or wrist-mounted transducer measurement systems can be misleading if it gives the impression that the vibration values can be used directly in operator risk calculations. If incorrectly used in this way, these values can dramatically underestimate the risks to operators which could lead to avoidable health issues and potentially serious repercussions should there be a claim.
If you need to carry out full HAV risk assessments (as well as measurements), there is a best practice guide checklist and open source template tool register available for download. We can also provide a full range of HAV training courses and workshops (up to full competency).