To: Directors of Environmental Health/ Chief Environmental Health Officers of London, Metropolitan, District and Unitary Authorities and Chief Executives of County Councils.

For the attention of: Environmental Services / Trading Standards / Fire Authorities / Other

This circular gives advice to local authority enforcement officers

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CHAIN SAW VIBRATION

INTRODUCTION

1 The incidence of Vibration White Finger (VWF) reduced in chain saw operators following the introduction of chainsaws fitted with anti-vibration mounts (AVMs) in the early 1970s. However HSE has become concerned about reports of VWF in full time operators who have always used chainsaws with AVMs. To obtain further information on possible causes of this phenomenon a joint project between the Research Laboratory Services Division of HSE (RLSD) and the Forestry Commission (FC) was undertaken in 1989/90 to investigate the vibration characteristics of modern anti-vibration chain saws. The aim was to establish:

(i) whether vibration levels from saws increased over their working life;

(ii) the typical daily vibration exposure of chain saw operators;

(iii) whether the standard laboratory test used to select low vibration chainsaws gave results relevant to exposure in normal forest use.

STUDY METHOD

2 Vibration exposure measurements were made on 10 chain saws of identical model commonly used by FC who selected them for their low vibration features compared with other saws. Five were used under normal working conditions, and 5 were tested in the laboratory for use as controls.

3 Throughout this project the saws were maintained in accordance with manufacturer's instructions and FC normal working practice. Chain cutting links were sharpened or replaced as necessary and anti-vibration mounts were changed after 3 months of use. The laboratory results were analysed to determine changes in vibration from data in 3 service states:

(i) "as return" (pre-service);	} monthly
(ii) "serviced' lie, with new bar/chain and sprocket fitted);	} monthly
(iii) "new anti-vibration mounts fitted";	} 3 monthly

No significant changes in vibration levels over the year of testing were found for any state of the saws.

4 The data for typical daily exposure, was calculated in 2 ways using either the highest (dominant) axis vibration level or the vector sum vibration level. This was done using laboratory and 'in-forest' measurements. Chain Saws do not have a truly dominant axis and the vector sum value is significantly larger than the highest single axis value.

RESULTS

5 Table 1 compares frequency weighted acceleration levels measured in the standard laboratory tests with those for related forest tasks. Levels measured in the forest on the rear handle with the saw idling are higher than those from the laboratory tests probably because the idle speed of the saws as set by the operators in the forest differed from that used for the laboratory tests. Results for cross-cutting are very similar showing good agreements between the two sets of data. Levels on the front handle for felling are higher than forest or laboratory cross cutting data possibly because during felling the saw is held on its side. Brashing and snedding are both operations where the saw spends most of its time operating at high engine speeds. These operations, are therefore, intended to be related to the standard test condition "racing". However the snedding and brashing results are not similar to the laboratory tests being more comparable to (but still higher than) the standard cross-cutting test measurements. Vibration measurements and time study data were combined to calculate typical 8-hour daily exposures and illustrated in Table 2.

DISCUSSION

6 The level of exposure to full time chain saw operators is likely to exceed 2.8 m/s² A(8) a level above which HSE recommends a programme of control measures and health surveillance.

SUMMARY

7 Vibration levels of well maintained chain saws did not alter significantly during the year of use. However typical vibration exposures on anti-vibration chain saws, selected because of their known low vibration properties, are still high enough to cause a significant risk of Hand-arm vibration syndrome (HAVS )(including VWF) to workers who use them daily.

ENFORCEMENT APPROACH

8 Full time and regular part time users and owners of chain saws should be advised:

(i) of the need to maintain the machine in accordance with the manufacturers instructions and in particular ensure that the anti-vibration mountings are changed at the specified intervals.

(ii) to use only chainsaws fitted with heated handles and AVMs.

(iii) that reduction in duration of exposure of workers will reduce the risk of VWF for a given vibration level. Breaks during periods of exposure also help reduce the risk.

(iv) of the need for pre-employment health assessment to identity conditions which may predispose to the development of HAVS. Also periodic health surveillance to detect early symptoms of HAVS. Employers should be advised to encourage users to report such symptoms when they appear, and it is recommended that workers have access to an occupational physician who can provide expert guidance on the health risks of vibration exposure in individual cases.

(v) that smoking is discouraged because it can increase the risk, or severity, of VWF.

(vi) that 'anti-vibration' gloves cannot be provided to reduce risks from vibration unless an assessment in accordance with Regulation 6 of the Personal Protective Equipment atWork Regulations 1992 has shown the gloves will be effective against vibration. 'Anti-vibration' or other gloves may be of value in keeping the wearer warm and dry, or may be desirable for other reasons eg physical protection.

(vii) that HAVS is reportable under the Reporting of injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR), once the diagnosis has been confirmed in writing by a doctor.

Furthermore, operators, supervisors, managers should be educated about HAVS, particularly the causes. ways of reducing the risk, and the symptoms.

FURTHER INFORMATION

HSG88 "Hand-arm Vibration"(£7.50)(a handbook for managers, engineers, health and safety professionals and occupational health specialists)

HSG170 "Vibration solutions" (£13.75)(a book of vibration reduction case studies)

INDG175(rev1) "Health risks from hand-arm vibration - advice for employers" (free leaflet)

INDG126(rev1) "Health risks from hand-arm vibration - advice for employees and the self employed"(free leaflet)

INDG296P "Hand-arm vibration syndrome" (a pocket card for employees)

"The successful management of hand-arm vibration" CD ROM (£95 +VAT) (ISBN 0 7176 1713 0)

These products are available through HSE Books, telephone: 01787 881165website: www.hsebooks.co.uk

UK 4407 "Hard to handle" (HAV video) (£64.57 inc VAT or 5 days rental £14.85 inc VAT)

The video is available through HSE videos, telephone 0845 741 9411

TABLE 1

AVERAGE FREQUENCY WEIGHTED ACCELERATION
(results in ms-²)

Laboratory			Forest
Test Mode	Vector sum		Task stage	Vector sum
(a) Front handle:
Idling	4.70		Idling	4.80
Cross-cutting	3.40		Cross-cutting Felling	3.0 5.7
Racing	1.90		Snedding Brashing	4.1 4.4
(b) Rear handle:
Idling	5.60		Idling	6.60
Cross-cutting	5.30		Cross-cutting Felling	4.6 5.0
Racing	2.60		Snedding Brashing	6.3 6.9

TABLE 2

DAILY EXPOSURE NORMALISED TO AN 8 HOUR DAY
(frequency weighted results in MS-²

	Laboratory				Forest
Axis	X	Y	Z	Vector sum	X	Y	Z	Vector sum
Front handle:	1.70	1.10	1.50	2.60	2.0	1.70	1.40	3.0
Rear handle:	1.30	2.20	2.10	3.30	1.4	2.60	2.30	3.8

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