By Jonathan Hill, 20Knots Plus
In July 2010 the EC Directive 2002/44/EC saw the implementation of the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration). The directive placed limits on exposure to both Hand-arm Vibration (HAV) and Whole Body Vibration (WBV).
HAV is a well-documented hazard and the resulting health risks are well understood. Industry is therefore able to plan and mitigate HAV exposure with the use of product data and the HAV vibration exposure calculator available on the UK HSE website (See HAV guide INDG175).
However, WBV is a wholly different issue – especially within the maritime sector and specifically for <24m craft operations. WBV within the directive is defined as the mechanical vibration that, when transmitted to the whole body, entails risks to the health and safety of workers, in particular lower-back morbidity and trauma of the spine.
The regulations placed a number of obligations on employers, the most important of these being to reduce exposure to As Low As Reasonably Practicable (ALARP). The directive places exposure limit values and action values for both HVA & WBV.
Whole Body Vibration (rms):
Exposure Limit Value (ELV) 1.15m/s2 A (8) the average over an eight-hour working day
Exposure Action Value (EAV) 0.5m/s2 A (8) the average over an eight-hour working day
Once these limit values were compared to maritime <24m craft data it was evident that the exposure was massively over the ELV by a large margin, some operations exceeding the EAV and ELV in minutes – not hours. With the complexity of measuring WBV on small craft the Maritime and Coastguard Agency issued a Marine Guidance Note (MGN) 436, Whole-Body Vibration: Guidance on Mitigating Against the Effects of Shocks and Impacts on small Vessels. The MGN is designed to help improve the design of vessels to reduce the severity of the WBV exposure and to provide a suitable postural position for those on board, and to enable them to brace effectively against the severe motions.
There have been a number of incidents on small vessels, which have resulted in investigations by the Maritime Accident Investigation Branch (MAIB). These have highlighted the different types of risks related to exposure to both WBV and Repeated Shock (RS) (See RACI Diagram). The different types of risk relate to the type of injury and its cause, within the maritime environment a single large or surprise impact can cause an acute catastrophic injury such as fractured or broken vertebra (See MAIB reports Celtic Pioneer, Ocean Ranger) which can identify a specific point in time and impact which caused the injury, whereas the exposure to continual WBV results in chronic long term injuries typically to crews and experience passengers.
With this magnitude of exposure the EU Directive gives guidance on the mitigation of exposure once initial assessments have identified a risk. As with MGN 436, it should start with investigating the task and vessel as to whether the hazard can be removed or replaced, i.e. moving from a small planning craft to a larger displacement vessel. Small commercial craft can have a long commercial life and are generally expensive for small maritime companies to replace, so we have yet to see any major enhancements in hull forms or types to reduce exposure.
Once the replacement of a craft has been ruled out, engineering solutions are more readily available. The maritime suspension seat market has grown massively over the last 10 years with numerous manufacturers from around the globe vying for custom. This has raised its own issues as up until now there have been no definitive testing for such seating so boat builders and operators are left with believing sales literature and their claims. The UK MOD has recently established a test protocol in order to address these issues and simplify its assessment and procurement process. There are other engineering solutions available including suspended decks and hull appendages to reduce both RS & WBV – as with suspension seating all of these solutions come with increased costs, maintenance and weight. Lots of organisations have already procured suspension seating to mitigate the risk of WBV & RS without fully understanding the problem or the effects of mitigation.
Jonathan Hill & Dr Trevor Dobbins, directors of 20 Knots Plus (20KTS+), have been delivering training in maritime WBV & RS over the last four years and have seen first hand the effects of WBV & RS and its mitigation. Initially the industry was unwilling to accept the levels established in the EU Directive, stating them as unobtainable or wrong. This has resulted in some organisations ignoring the legislation altogether. Some companies simply procured suspension seating without full understanding the effects and their employees still report lower back pain and soreness even with mitigation. This can be generally linked to not educating its personnel and giving them the ability to increase their average speed therefore allowing them to still drive at their level of “tolerable discomfort”.
20KTS+ delivers a One Day WBV & RS Awareness Course which educates both managers, crews and passengers alike on all aspects of RS & WBV from the exposure chain, its health effects, mitigation through administration, education & training (EU Dir Article 6) and health surveillance (EU Dir Article 8).
There is little effective treatment for chronic injuries caused by WBV & RS, however early action taken by employers can help to reduce the severity of such injuries. With correct mitigation, education and health surveillance the crews and passengers having bad knees and backs should no longer be the norm.
Jonathan is the director of training for 20 knots Plus and a former Royal Marine Warrant Officer serving 23 years before retiring and setting up 20kts+ to support the <24m / high-speed craft sector.
It’s difficult to find knowledgeable people on this topic, however, you sound like you know what
you’re talking about! Thanks
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