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Hand arm Vibration in Forestry and Arboriculture

Introduction

The Control of Vibration at Work Regulations 2005 (CVWR 2005) apply to both vibration entering the hand and arm from hand-held power tools and vibration of the whole-body through the seats of vehicles. This article concentrates on the issues relating to hand-arm vibration.

Background

Hand-arm vibration (HAV) may be generated from powered hand-held and hand-guided machines such as chainsaws, brush-cutters and stump-grinders. Long-term exposure to high levels of hand-arm vibration can cause damage to the hand. Many will have heard of vibration-white-finger where the blood circulation is affected by the vibration exposure. Other damage may be caused to the nerves and muscles in the hand and the tendons in the wrist (carpal tunnel syndrome). Together the damage produced by vibration exposure is referred to as hand-arm vibration syndrome or HAVS.

The Regulations require 4 main actions of employers:

The main requirement is to control risk. Controls must be introduced for workers in jobs with a history of risk, such as forestry and arboriculture, and for any workers exposed to vibration at or above the daily Exposure Action Value (EAV) set at 2.5 m/s² A(8). Exposure above the daily Exposure Limit Value (ELV) of 5 m/s² A(8) is prohibited. [Note – capitalisation changed for consistency with Example boxes]

The risks to health from hand-arm vibration have been recognised in the UK for many years.  Full guidance on what should be done to comply with the CVWR 2005 is contained in HSE guidance book ‘Hand-arm Vibration’, L140 and can be downloaded or purchased from the HSE website www.hse.gov.uk/vibration. The website also provides further examples of how risk from vibration can be controlled.

HAV risks in arboriculture and forestry

Vibration exposure in arboriculture and forestry arises from many power tools, such as:

The use of power tools in forestry and arboriculture should be considered a risk. And actions to minimize the risks should be implemented. In practice these actions are likely to be combinations of engineering and management control measures.   

Vibration control

Having decided that there is a risk of vibration injury then engineering and management control must be implemented to control the risk.

Alternative methods for performing the job. 

It is unlikely that there will be much opportunity to change the way the job is done. However, with some thought some improvements may be possible. In one example an arboriculturalist decided to minimise the use of powered hand tools by transporting felled wood to a base site for processing using larger static machinery.

Low-vibration alternative tools may be available. 

Historically, chainsaw vibration emission was very high.  Advances in technology applied by the major manufacturers have greatly reduced vibration emissions over past decades.  For example, improved engine mounting systems, changes in chain design, heating of handles, etc. have all contributed to reduced risk of vibration disease in chainsaw operators.

With many types of machinery the technology is stable and there may be little to choose between the vibration emissions of directly competing machinery.  You should draw up a shortlist of machinery suitable for the job and then consider the vibration emissions reported by the manufacturer.  You should reject any machines from your shortlist with unusually high vibration emission, for example if vibration emissions for one machine type generally lie between 6 and 8 m/s², a machine that has, say, a  12 m/s² emission value should be avoided.  You should consider the vibration when purchasing or hiring machines and accessories.

Training and maintenance

As with all power tools, training in the correct use of the tool is important for controlling vibration exposure. The forces applied to the tool while cutting should be appropriate for the job and the choice of equipment should help reduce grip and feed forces to a minimum. Operators need to be aware of maintenance requirements and when blades need to be replaced or service.

Maintenance is particularly important for forestry and arboriculture tools. For Chainsaws it is important to keep the chains sharp and properly tensioned. For saws and cutters, bent or damaged blades should be replaced. Engine mountings should be maintained and replaced in accordance with manufacturers’ instructions.

Limiting exposure time

In cases where use of high vibration machinery is unavoidable it may be necessary to limit the duration of exposure.  For example, mechanical scythe/hand-guided shears might have a vibration emission of around 10 m/s2, setting a usage limit of 30 minutes for this tool would prevent the exposure action value of 2.5 m/s² A(8) being exceeded (provided no other vibrating tools are used during the working day).
Setting a limit on exposure duration requires reliable vibration emission information and a good knowledge of the likely daily exposure duration.

Regular breaks are likely to reduce the risk; it is better to have many short periods of operation than to have a few long periods of operation. Opportunities should be taken to exercise the hands and fingers to encourage good blood circulation, for example when re-filling fuel tanks or changing blades.

Daily exposures

From the nature of the work in arboriculture and forestry and the durations of use of powered hand-tools, it is likely that vibration exposures will be above the exposure action value of the CVWR and possibly around the exposure limit value. It can be helpful to estimate vibration exposures, for example, to confirm priorities for reducing exposures.

Example 1:  Use of a chainsaw in forestry

  • A chainsaw is used for a clear-felling operation, the typical hands-on time for this operation has been shown to be about 4 hours.
  • The manufacturer gives separate emission data for both handles, the highest of these values is 6.6 m/s². The daily exposure is then 4.7 m/s² A(8), that is above the Exposure Action Value and close to the Exposure Limit Value of the CVWR:

Example 1:  Use of a chainsaw in forestry

Daily exposure, the A(8) value,  is calculated from the estimated vibration magnitudes and corresponding exposure times.  Full details are given in International and European Standards (BS EN ISO 5349-1 and BS EN ISO 5349-2).  One tool for calculating exposure is a spreadsheet calculator which may be downloaded from the HSE website.  Examples of the use of this calculator are shown in Examples 1 and 2. 

Example 2:  Use of a brushcutter and chainsaw in ground maintenance work

  • A brushcutter is used for 3½ hours per day. The manufacturer gives the vibration emission of this saw as 4 m/s². The daily vibration exposure contribution from the brush cutter is 2.6 m/s² A(8).
  • The worker also makes some use of the chainsaw (emission value of 6.6 m/s²). This is for occasional clearance work and the exposure time is less than 30 minutes. The daily vibration exposure contribution from the chainsaw is 1.7 m/s² A(8).
  • The use of the two tools together in one day gives a total daily exposure of 3.1 m/s² A(8), that is above the Exposure Action Value of the CVWR.

Example 2:  Use of a brushcutter and chainsaw in ground maintenance work

Vibration magnitudes

The manufacturers of power tools are required by the Supply of Machinery (Safety) Regulations to provide information about risks from vibration. Part of this information on vibration risks is a statement of the vibration emission, which must be included in the instruction manual for the machine.

Vibration emission value information provides a good starting point for carrying out a exposure assessment for combustion-engine machines such as those used in forestry and arboriculture tools.

Further information on likely vibration magnitudes for forestry machines can be found in ISO/TR 22521:2005.

There are several types of data that may be provided by machine manufacturers. Information on how to use this data appears on the HSE vibration web site and is included in the HSE guidance on the regulations (L140).

Exposure times

Personal protective equipment

There is no personal protective equipment that can be shown to reduce the risks from hand-arm vibration. “Anti-vibration” gloves are available, but at best will only provide a small reduction in vibration exposure. Gloves must not be provided as a means of reducing vibration risk unless vibration exposure reduction has been demonstrated. Some workers like the feel of anti-vibration gloves and they can be used to protect against abrasion and to keep the hands warm.

Keeping the hands and body warm and dry is likely to reduce the risks from hand-arm vibration because this helps ensure that good blood circulation is maintained throughout the body and especially in the hands and fingers. In outdoor working it is advisable to use gloves, body warmers and layered clothing to maintain a good body and hand-arm temperature.

Health surveillance

The regulations require health surveillance where workers are considered to be at risk. Any worker exposed above the 2.5 m/s² A(8) action level is entitled to health surveillance.  Health surveillance must include access to an occupational physician.

It can be difficult to pinpoint who is at risk from vibration exposure because of uncertainties in knowledge of personal exposure and in differences in individuals’ susceptibility to vibration injury.  Health surveillance helps prevent workers developing significant handicap, for example, if the vibration risk has been underestimated.

HSE advises a tiered approach to health surveillance. The first step is for workers to receive a questionnaire-based interview (upon employment and then annually) designed to identify possible early symptoms. Workers who show signs of possible injury go on to more detailed investigations.

Health surveillance is likely to reveal symptoms in workers who have used designs of tools with high vibration emissions and hence had high vibration exposures in the past.  Health surveillance of these workers should be used to check that symptoms of HAVS are not advancing. 

Preventing disability

Good work has already been done to develop effective techniques for preventing HAV injury in forestry and arboriculture. Working in compliance with the CVWR and following HSE guidance will help prevent the disabilities caused by hand-arm vibration.

Further reading

BS EN ISO 5349-2.  Mechanical vibration and shock – Measurement and evaluation of human exposure to hand-transmitted vibration – Part 2: Practical guidance for measurement at the workplace. British Standards Institution (2002)

2012-11-21