noise control wood chipper.pdf

Executive Health and Safety

Noise emissions and exposure from mobile woodchippers

Prepared by Health and Safety Laboratory for the Health and Safety Executive 2008

RR618 Research Report



Liz Brueck BSc, MIOA Health and Safety Laboratory Harpur Hill Buxton Derbyshire SK17 9JN

Mobile wood chipping equipment used in forestry and arboriculture generates high levels of noise. Sustained excessive noise exposure leads to gradual hearing damage. This damage results in deafness and tinnitus. Under the Control of Noise at Work Regulations 2005 there is a requirement to control noise exposure by technical and managerial means with hearing protection only used as a last resort.

An important noise control measure is the selection of quieter machines. Noise emission data provided by the machine manufacturers and suppliers should enable this selection. Manufacturers are obliged to ensure low noise designs and to provide values for the noise emission under stated operating conditions. It is also recognised that the real world operating conditions will also influence the noise emission and the noise exposure of the operator.

The Health and Safety Laboratory performed measurements of the noise emission and operator noise exposure of a range of mobile, hand fed, wood chippers under simulated standard and real world operating conditions. These measurements were made on behalf of the Forestry Commission and Jason Liggins of the Health and Safety Executive’s Policy Group - Agriculture and Food Section.

The main aims of the work were:

1. To provide information on the noise emission from a range of wood chipping equipment under a range of set, typical use conditions.

2. To provide information on noise exposures from use of this equipment, and the operational factors which influence this including, but not limited to, materials being processed, methods of infeed and position of operator.

3. To ascertain whether there are significant variations between manufacturer’s declared noise emissions and emissions under typical use.

This report describes the noise measurement procedure and details the results. Technical terms used in this report are explained in a glossary at the end of this report.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

HSE Books

© Crown copyright 2008

First published 2008

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner.

Applications for reproduction should be made in writing to:Licensing Division, Her Majesty’s Stationery Office,St Clements House, 2-16 Colegate, Norwich NR3 1BQor by e-mail to [email protected]

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ACKNOWLEDGEMENTS Thanks are due to James Archer of Tilhill and Paul Webster of Forest Research. They provided invaluable expertise as well as the machines, timber, and facilities used in this trial.

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CONTENTS

1 INTRODUCTION......................................................................................... 1

2 LEGAL DUTIES FOR MANUFACTURERS AND SUPPLIERS, AND STANDARDS FOR WOODCHIPPERS ............................................................. 22.1 Noise control............................................................................................ 22.2 Noise test code ........................................................................................ 3

3 SELECTION OF WOOD CHIPPERS FOR USE IN THE STUDY ............... 4

4 MEASUREMENT PROCEDURE ................................................................ 64.1 Operating conditions................................................................................ 64.2 Measurement conditions.......................................................................... 6

5 RESULTS ................................................................................................... 85.1 Sound power results ................................................................................ 85.2 Operator position sound pressure level ................................................. 105.3 Frequency content of the chipper noise................................................. 125.4 Direction of the chipper noise ................................................................ 125.5 Half length timber in standard test ......................................................... 125.6 Manufacturer’s Data .............................................................................. 13

6 MATTERS RAISED BY THE RESULTS................................................... 146.1 Possible impacts WITH HOPPER ......................................................... 146.2 Suitability of noise test code .................................................................. 146.3 Quiet machines...................................................................................... 156.4 Operator hearing protection................................................................... 156.5 Manufacturers’ noise data ..................................................................... 16

7 CONCLUSIONS........................................................................................ 17

8 RECOMMENDATIONS............................................................................. 18

9 REFERENCES.......................................................................................... 19

10 APPENDIX A FREQUENCY SPECTRA ............................................... 20

11 APPENDIX B – CHIPPER PHOTOGRAPHS ........................................ 31

12 GLOSSARY .......................................................................................... 42

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EXECUTIVE SUMMARY

Objectives

1. To provide information on the noise emission from a range of wood chipping equipment under a range of conditions of typical use.

2. To provide information on noise exposures from use of this equipment, and the operational factors, which influence this including, but not limited to, materials being processed, methods of feeding of materials and position of operator.


Main Findings

1. Operators may be exposed to sound levels reaching 107dB(A) during typical use. Levels can be reduced to between 95 and 100dB(A) if noise controls seen on a prototype machine are applied. Noise emission is also directional with most noise generally being in the direction of the hopper and the operator.

2. Noise emission is dependent on type of material being processed, especially in the infeed hopper direction. Untrimmed material with soft branches is quieter than trimmed logs. The square cut timber specified by the C standard (BS EN 13525:2005) noise test code creates additional, often dominant, high frequency noise. It is thought these noise characteristics arise from impacts in the infeed hopper.

3. Few manufacturers and suppliers provide noise emission data with details of the applicable operating conditions.

Recommendations

1. Effective noise controls seen in a prototype model woodchipper should be applied to other models to reduce noise emission and operator exposure.

2. Users need access to complete noise emission data to allow selection of quiet machines. HSE should encourage the provision of this data as required by regulations.

3. The noise test code in the C standard would benefit from revision, to include a more realistic wood and reporting of the average emission rather than selected values.

4. Simple noise controls to the hopper should be tried on machines showing strongly directional noise to the hopper side.

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1 INTRODUCTION



The Health and Safety Laboratory performed measurements of the noise emission and operator noise exposure of a range of mobile, hand fed, wood chippers under simulated standard and real world operating conditions. These measurements were made on behalf of the Forestry Commission and Jason Liggins of the Health and Safety Executive’s Policy Group – Agriculture and Food Section.






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2.1

LEGAL DUTIES FOR MANUFACTURERS AND SUPPLIERS, AND STANDARDS FOR WOODCHIPPERS

Under the Supply of Machinery (Safety) Regulations 1992 manufacturers and suppliers of machinery have a legal duty to produce machinery with minimized noise emissions, and to provide information on the noise emitted.

As an aid to compliance EN ISO 12100-1 defines a range of standards to specify the safety requirements for machinery and equipment. Within this range C-standards relate to specific types of machinery and equipment. C-standards define the range of design and construction criteria related to the safety requirements and give verification tests for these. The C-standard for wood chippers is BS EN 13525:2005. This standard includes examples of how and where noise may be controlled and a noise test code for the determination of the noise emission and the operator noise exposure.

Manufacturers may choose to follow part or all of the C-standard, or choose to comply directly with the regulations by other means – so for example declare noise according to the standard test method, or declare using their own appropriate test method.

NOISE CONTROL

In section 4.4.1 the BS EN 13525:2005 considers noise sources and noise controls. The text is quoted below. The paragraph numbering is as given in the standard.

4.4.1.1.1 Noise reduction at source by design and by protective measures

The machine shall generate a noise level as low as practicable. The methodology for designinglow-noise machinery described in EN ISO 11688-1 shall be used.

The main sources causing noise in wood chippers include e.g.

Infeed mechanism;

Chipping components;

Chip discharge;

Power source

The noise reduction measures by design include e.g.

Selecting low noise components e.g. engine;

Selecting proper materials;

Selecting proper thickness and coating of surfaces;

Optimisation the knife mounting configuration;

Optimisation of the knife/feeding angle;

Selecting low noise exhaust system.

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2.2

4.4.1.1.2 Noise reduction by information

If after taking all possible technical measures for reducing noise at the design stage a manufacturer considers that further protection of the operator is necessary, then the instruction handbook shall:

Recommend the use of low-noise operating modes, and/or limited time operation;

Give a warning of the noise level and recommend the use of ear protection.

NOISE TEST CODE

The noise test code in EN 13525:2005 requires the noise emission of the wood chipper to be obtained from sound pressure level measurements over a hemispherical surface around the wood chipper, over a hard reflecting ground surface. The sound pressure level measurements are used to determine the A-weighted sound power over a specified work cycle.

The operator’s noise exposure is determined using the same specified work cycle as the noise emission assessment.

The specified work cycle defined by the noise test code is quoted below. The paragraph numbering is as given in the standard noise test code.

B.5.2 The measurements shall be done over one complete cycle of the chipping work. The machine shall be operated within 10% of its maximum rated rotational frequency. Provisions to monitor this during measurements shall be made and be recorded in the test report.

B.5.3 The measurements shall be made while chipping a 4 m long (50 ± 10) mm x (50 ± 10) mm air dry, moisture (18 ± 3) %, pine or equivalent wood at maximum infeed speed of the machine. The infeed has to be continuous in order to achieve a measuring period of at least 10 s. The work cycle begins when the wood meets the blades and ends when all the wood is chipped. At the end of the cycle the operator is ready to infeed another wood into the chipper. After feeding the test piece the operator remains standing upright at the position where the feeding was performed. The machine blade setting shall be recorded and reported in the test report. Chips shall be blown 90° clockwise in relation to the feed.

B.6 Tests shall be repeated until three consecutive A-weighted results give values within 2dB.

BS EN 13525:2005 and its noise test code is not applicable to wood chippers manufactured before the date of publication of the standard by CEN.

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3 SELECTION OF WOOD CHIPPERS FOR USE IN THE STUDY

Chippers may be designed as utility or wood fuel types. There are also three types of chipping mechanism used;

Disc, rotating knives sometimes fixed to a backing plate for support,

Drum, knives mounted around the inside of a drum,

Screw, a spinning conical screw with sharpened outer edges that both cuts and provides the infeed mechanism.

Most mobile wood chippers are utility machines and most wood chippers use a disc type chipping action.

Eleven wood chippers were selected for the study. Of the eleven selected, ten were disc type and one was a drum action chipper; nine were utility; two were wood fuel types. No screw type chippers were included as this design is obsolete and only a few examples are still in use. Tracked models with caterpillar tracks for independent movement, road tow models towed by another vehicle, and PTO (power take off) models powered from a tractor during chipping were all included. All woodchippers were supplied with freshly sharpened blades.

The woodchippers are identified by letter designation as given in Table 1. Woodchipper D was a prototype on which the manufacturer had added additional noise controls; all other machines were normal production models. Two versions of woodchipper C were tested; a tracked model and a road tow model.

Appendix B has photographs of the machines.

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Table 1 Wood chippers selected for use in the study All woodchippers were utility type unless stated otherwise ID Type Engine/ PTO Chipping Max. Cutting Infeed No. of

Speed Type Diameter Angle Knives (inches)

A Wood fuel PTO 550 rpm Drum 12 (height) 14 (width)

90º Not applicable

B PTO 1000 rpm Disc 12 90º 6

C Tracked 35hp diesel Disc 6 90º 2

C Road tow 35hp diesel Disc 6 90º 2

D Road tow prototype 50hp diesel Disc 7 90º 4 with added noise engine blades controls

E Road tow 34hp turbo diesel engine

Disc-blades

6 90º 4

F Tracked 50hp diesel engine

Disc-blades

7 90º 4

G Road tow 34hp diesel engine

Disc 6 90º 2

H Tracked 50hp diesel engine

Disc 9 90º 2

I Wood fuel PTO 1000 rpm (Valtra 6550)

Disc 10 45º 2

J Road Tow 28hp diesel engine

Disc 6 90º 2

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4.1

4 MEASUREMENT PROCEDURE

OPERATING CONDITIONS

The chippers were tested in an open area away from other noise sources and obstructions likely to cause significant reflections. The ground was flat and hard, providing a reflecting ground plane over the whole measurement area.

Logs of fresh trimmed (no twigs) and untrimmed (with twigs and small branches) hard wood and soft wood were used to represent typical working materials. Several lengths were fed one by one into the wood chipper providing a continuous period of chipping for around one minute. Table 2 gives the wood description provided by Forest Research and the moisture content determined after chipping.

Table 2 Description of wood used for chipper trial

Report description Wood Dimensions Moisture content %

Standard Square sawn 50mm x 50 mm x 4.8m 13 Untrimmed soft wood

Scots Pine tops

12cm average butt diameter x 4.0m 64

Trimmed soft wood Scots Pine 10 cm average butt diameter x 2.8m (range 6 –14cm)

63

Untrimmed hard Birch tops 8cm average butt diameter x 6m (range 5 – 44 wood 11cm) Trimmed hard wood Birch 11cm average butt diameter x 2.8m (range 6

–16 cm) 46

To reproduce the operating conditions required by the standard noise test code measurements were made while cutting single 4.8m lengths of 50mm square cut pine. From 3 to 5 repeat measurements were taken with each machine. Some additional measurements were also made using 2.4m lengths of 50mm square cut pine to check the effect of timber length.

The utility chippers were run at maximum infeed speed throughout. This is typical of normal use. The wood fuel chippers were run at both mid and maximum infeed speed, which is again within the range typical of normal use.

4.2 MEASUREMENT CONDITIONS

4.2.1 Noise measurements

Sound pressure level measurements to estimate the noise emission of each chipper were made at four locations 6 to 8m from the centre of the chipper at a height of 1.5m. Figure 1 shows the approximate positions. Position 1 was in front of the hopper, and slightly off centre to avoid shielding by the operator. Positions 1 and 2 remained fixed having clear line of sight to the chipper; positions 3 and 4 were varied for different chippers to ensure clear line of sight remained when tractors and towing vehicles were used with the operating chipper.

At least two additional measurements above the height of the chipper would be required for the full assessment of the noise emission under the standard noise test code. The results here are intended to provide an estimate of the noise emission as it affects nearby operators, and do not consider any directional characteristics of noise emitted upwards from the chipper.

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1

operator 2

4 3

Infeed hopper

discharge

Figure 1 Approximate measurement positions around chipper

CEL 360 noise dosemeters at each measurement position recorded the A-weighted Leq, and C-weighted peak level. Data were record continuously at 2-second intervals to allow the results for each different operation to be extracted during post measurement analysis.

The operator’s noise exposure was recorded using a CEL 460 noise dosemeter with the microphone fitted at the end of the shoulder. This recorded the A-weighted Leq, and C-weighted peak levels at 5-second intervals.

In addition the noise in front of the hopper at position 1 was analysed using a B&K 2260 sound level meter / analyser. This provided frequency analysis of the noise.

4.2.2 Moisture content

Samples of the chipped wood were immediately bagged after chipping for analysis of the moisture content. These values were obtained by measurement of a sample weight before and after drying.

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5.1

5 RESULTS

SOUND POWER RESULTS

The A-weighted Leq for each operation was obtained from the time history recorded by each dosemeter around the machine. The Leq was recorded for approximately one minute’s continuous chipping for operations representing normal working. To assess the variation in the noise emission over the period the Leq was also recorded for each individual infeed cycle within the period. The Leq for the standard test material was for a period chipping a single piece of wood, lasting from the start of feed of the wood to the end of the chipping. This period was typically 5 to 10 seconds.

Sound power is a measurement of the total noise emitted by a machine. For a sound source and measurements over a hard reflecting ground plane:

Sound power Lw = Leq + 20 log r + 7.8dB

Where Leq is the time averaged sound pressure level at a distance r in metres from the source centre.

The sound from the chipper is directional with the highest levels generally being in front of the hopper. The overall sound power was calculated as the average of the sound power values for the four different directions as below:

Overall sound power Lwtot = 10 log (10Lw1/10 + 10Lw2/10 +10Lw3/10 +10Lw4/10 )/4

Where the standard test conditions have been reproduced a sound power value has been obtained for each piece of test wood chipped. This has provided a range of values. The value reported is the mean of the first three consecutive values that are within 2dB as required by the standard noise test code.

Plots of the sound power for each machine and wood type are shown in Figure 2. The machines are shown in the order of testing. Table 3 gives the same data as numerical values together with the standard deviation of the sound power taken from the results for each infeed cycle within the period.

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Table 3 Noise emission dB(A) of woodchippers with different wood and standard deviation calculated for individual infeed cycles within operating period.

ID Type Trimmed Untrimmed Trimmed Untrimmed Standard wood softwood softwood hardwood hardwood Overall Std Overall Std Overall Std Overall Std Mean Std

dev dev dev dev of three dev A Wood fuel PTO 115.5 0.9 114 0.5 116.5 0.5 114 1.2 115 0.8

max 114 mid

0.1

B PTO 118 0.8 117 0.3 119.5 0.9 115.5 0.9 120.5 0.4

C Tracked 118.5 0.4 117 0.7 120.5 0.9 117.5 2.0 124.5 1.2

C Road tow 117.5 0.4 112.5 1.1 118 0.4 115.5 1.4 123 0.9

D Road tow prototype 113.5 0.5 112.5 1.1 114 0.9 110.5 0.3 117.5 1.0 with added noise controls

E Road tow 117 1.5 117 0.4 118.5 1.0 115.5 1.8 123.5 1.0

F Tracked 120 0.8 118 0.4 120 0.7 117 0.8 120 0.8

G Road tow 118 0.7 117 0.1 118.5 0.4 117.5 1.2 122.5 0.9

H Tracked 121 0.7 116 2.4 119.5 1.4 117 0.2 123 1.4

I Wood fuel PTO 118 0.9 117 0.5 119.5 0.5 117.5 0.7 118 0.6 max 116 mid

1.7

J Road Tow 118.5 0.4 115.5 1.4 117.5 0.5 116.5 0.6 119.5 0.6

Note: All chippers were run at maximum infeed speed throughout except for woodchippers A and I. Woodchipper A was run at mid infeed speed for the trimmed and untrimmed hard and softwood. The standard wood results were obtained at maximum and mid infeed speeds for both the woodchippers A and I.

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5.2

A B D E F G H I J

(A

i

i

i

100

105

110

115

120

125

130

C tr

acke

d

C ro

ad to

w

Chipper

Soun

d po

wer

dB Tr mmed softwood

Untr mmed softwood

Tr mmed hardwood

Untrimmed hardwood

Standard

Figure 2 Noise emission of wood chippers

OPERATOR POSITION SOUND PRESSURE LEVEL

The operator’s noise exposure has been taken from the dosemeter worn on the shoulder. The A-weighted Leq for each operation has been obtained from the time history over the same period as the noise emission measurement. Again the normal wood results are over an approximately one minute period of continuous chipping while the standard result is the mean of three selected consecutive readings with single lengths of wood.

The Leq for each machine and wood type are shown in Figure 3.

85

90

95

100

105

110

115

A B D E F G H I J

(A

i

i

C tr

acke

d

C ro

ad to

w

Chipper

Soun

d pr

essu

re le

vel d

B

Tr mmed softwood

Untrimmed softwood Tr mmed hardwood

Untrimmed hardwood

Standard

Figure 3 Sound pressure level measured on operator

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Corresponding numerical values to the results in Figure 3 are given in Table 4. Table 4 also includes an indication of the variation in sound pressure level. For normal hard and soft wood this is the difference in Leq for consecutive 30-second periods over the operating period. For the standard wood it is the standard deviation for all individual infeed cycles. The infeed cycle standard deviations are not reported for the normal wood, as operator actions around the chute also cause other significant variations.

Table 4 Operator position sound pressure level dB(A)

ID Type Trimmed softwood

Untrimmed softwood

Trimmed hardwood

Untrimmed hardwood

Standard wood

Overall Leq

30s Leq spread

Overall Leq

30s Leq spread

Overall Leq

30s Leq spread

Overall Leq

30s Leq spread

Mean Leq of three

Std dev

A Wood fuel PTO

100 2 96.5 1 100 1 97 1 99 max 99.5 mid

3.8

2.1

B PTO 104.5 1.5 103 2 107 0.5 100 0.5 106.5 1.0

C Tracked 105.5 1.5 102 3 107.5 1 104.5 0.5 109.5 2.3

C Road tow

106 1 101 2.5 107.5 0 105 1.5 109 0.5

D Road tow prototype with added noise controls

99 1 97.5 3 99 0 96 1 102 0.8

E Road tow

104 1 102.5 3.5 105.5 2 100 0 107 0.4

F Tracked 103 1 101 1 105 0.5 101 1.5 103 1.0

G Road tow

104.5 2.5 101 2 105 0.5 103 1 103.5 0.1

H Tracked 105 2 100.5 5.5 102.5 2 100.5 1 103 1.9

I Wood fuel PTO

102.5 1.5 100 1.5 104.5 2 101.5 0 100 max 94.5 mid

1.6

0.4

J Road Tow

104 0.5 105 5 104 0.5 101 2 98.5 1.2

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5.3 FREQUENCY CONTENT OF THE CHIPPER NOISE

The 2260 sound level meter at position 1, facing the hopper, recorded the noise spectra as the unweighted Leq in third octave bands. These spectra are shown in Appendix A of this report.

5.4 DIRECTION OF THE CHIPPER NOISE

Table 5 compares the difference in level at the hopper side (position 1) with positions 2, 3, and 4 to the side and rear. The range of values given is the difference between the sound power calculated from the LAeq at position 1 relative to positions 2, 3, and 4. As this difference is calculated from the predicted sound power for each direction it is independent of the actual measurement distance used. Positive values indicate a higher sound power in the direction of position 1, negative values indicate a lower value in the direction of position 1. The three values reported are in the order of position 2, 3, and 4. Readings were taken for each piece of standard wood and the values given are the average of the results for each piece.

Table 5 Sound pressure level at position 1 on the hopper side relative to positions 2, 3, and 4 to the side and the rear dB(A)

ID Type Trimmed soft wood

Untrimmed soft wood

Trimmed hard wood

Untrimmed hard wood

Standard timber

A Wood fuel PTO 3.5, 3.0, 3.0 1.0, 0, 0.5 2.5, 2.5, 2.5 3.0, 2.0, 2.5 6.5, 7.0, 7.5

B PTO 3.0, 3.0, 4.5 2.5, 1.5, 4.0 3.5, 3.0, 5.5 3.0, 1.5, 4.5 7.0, 7.5, 9.0

C Tracked 7.5, 8.5, 8.5 6.5, 7.0, 7.5 8.0, 9.5, 9.5 9.0, 9.5, 10.5 11.0, 12.5, 13.1

C Road tow 5.0, 7.0, 7.0 3.5, 3.5, 4.5 5.0, 6.0, 7.0 5.5, 5.5, 7.0 7.5, 9.5, 10.5


2.0, 2.0, 4.5 2.0, 2.0, 4.5 2.0, 2.5, 5.0 2.5, 1.5, 4.0 2.5, 3.5, 6.0

E Road tow 6.0, 6.5, 8.0 7.5, 7.5, 8.0 5.5, 7.0, 7.5 7.5, 6.5, 7.5 5.0, 11.0, 12.0

F Tracked 3.5, 3.0, 4.5 2.0, 1.0, 3.0 3.5, 3.0, 4.5 2.0, 1.0, 2.0 4.0, 5.5, 7.0

G Road tow 4.0, 5.0, 6.0 3.5, 3.5, 5.0 4.0, 5.0, 6.5 5.0, 6.0, 7.5 7.0, 11.0, 12.0

H Tracked 8.5, 8.5, 8.0 6.5, 5.0, 5.0 8.5, 8.0, 8.0 8.5, 7.5, 7.5 10.0, 10.5, 10.5

I Wood fuel PTO 2.0, 0.5, 1.5 3.5, -1.5, -0.5 2.0, 1.0, 1.5 1.5, -0.5, 1.0 2.0, 1.1, 2.0

J Road Tow 6.5, 7.5, 8.0 5.5, 6.0, 7.0 7.0, 7.5, 8.5 7.5, 7.5, 9.0 9.0, 10.0 , 10.5

HALF LENGTH TIMBER IN STANDARD TEST

4.8m lengths of timber were used to simulate the standard test given in the noise test code. It was thought that the noise might be altered if a shorter length were used. Additional tests were

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5.5

5.6

performed on woodchipper E and woodchipper G using the standard timber in 2.4m lengths. The results show no discernable change in the noise emission with the change in length.

MANUFACTURER’S DATA

UK suppliers or manufacturers of the models of machine tested were asked for the noise emission and operator sound pressure level data together with the operating conditions applicable to the data.

The result of these enquires is given in Table 6.

Table 6 Noise data available from manufacturers and suppliers

ID Type Sound power dB(A)

Operator sound pressure level dB(A)

Comments

A Wood fuel PTO

Not available

Not available

The supplier had no data and had requested data from this trial

B PTO 115 Not available

Manufacturer supplies sound power and sound pressure level at 10m distance within handbook together with details of test conditions. This data was obtained chipping 120mm square, 1.5m lengths of Corsican Pine.

The operating conditions used for this measurement are not in accordance with BS EN 13525:2005. A representative of the company was of the opinion that this was still a draft standard.

C Tracked 119 Not available

C Road tow 119 Not available


Labelled as 91

Not available

Contacted manufacturer by e-mail for data. No information on operating conditions supplied.

E Road tow Not available

Not available

F Tracked 120 Not available

G Road tow 115 Not available

Supplier had no further information on operating conditions. No response from manufacturer.

H Tracked 114 Not available

Supplier had no information on operating conditions for labelled sound power. Contacted importer for further information, and had no response.

I Wood fuel PTO

120 102 Supplier obtained information from manufacturer. Information specified as in accordance with CEN/TC144 WG8N16

J Road Tow 121 106 The European and UK dealers were unable to supply the information. The manufacturer provided data obtained in accordance with EN13525.

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6 MATTERS RAISED BY THE RESULTS

6.1 POSSIBLE IMPACTS WITH HOPPER

The results show dependence on the type of wood being chipped. Generally the trimmed wood was noisier than the untrimmed tops. Where such differences were seen the thin square cut wood used to simulate the standard test conditions gave a higher noise emission than the trimmed logs (see Figures 2 and 3). It is suspected that these differences are due to impacts in or with the infeed hopper for the following reasons:

• Machines having significant differences in noise emission with wood type are also shown in table 5 to be generally directional in the noise emission towards the hopper side.

• In Appendix A Figures A1 to A11 show the changes in noise level with the wood type are occurring in the region above 500Hz. These frequencies are too high to be associated with the engine or chipping speed.

• The noise when chipping the standard wood is generally showing more pronounced directionality in the hopper direction, and a dominance of higher frequencies (Figures A1 to A11). Given that this wood is springy and hard it may be impacting more often than other wood, and providing less damping of impacts with the hopper.

• The noise when chipping untrimmed branches is generally lower, and with less pronounced directionality in the hopper direction. It is possible that the thin soft material damps the noise from the hopper.

• The road tow version of wood chipper C carries a spare wheel on its hopper. This version is significantly quieter than the tracked version without a spare wheel on the hopper. It is thought probable that the spare wheel is providing noise damping to the hopper.

• Chippers that show strong directionality to the hopper side and a wide range of noise emissions for different wood types are those most likely to benefit from damping of the hopper or a change of hopper design to reduce impacts. Reduction of noise from the hopper will have a direct benefit to the operator working by the hopper.

6.2 SUITABILITY OF NOISE TEST CODE

The noise test code in BS EN 13525:2005 is designed to provide repeatable test conditions for determination of the sound power of the chipper and sound pressure level at the operator’s position. It is essential for the noise test code result to allow quiet and noisy machines to be correctly identified.

6.2.1 Noise emission

Figure 2 shows the sound power when chipping the wood defined by the test code and during normal use. The sound power difference between these different wood types varies between machines. For five machines the standard wood emission results are comparable to the nosiest real world conditions, for the remaining six machines it is significantly higher. The noise test code however correctly identifies the woodchipper A and the prototype woodchipper D as the quietest machines in terms of noise emission.

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6.2.2 Operator exposure

The standard wood provided the highest sound pressure level at the operator’s position for four of the eleven machines and an underestimate of the exposure for two out of the eleven machines. In terms of operator exposure woodchipper A and woodchipper D are both significantly quieter than the other machines chipping normal wood. With the standard wood woodchipper D is not found to be significantly quieter at the operator position than all but four of the eleven machines tested.

6.2.3 Frequency content of sound

The standard wood is giving rise to dominant high frequency sound in the hopper direction with nine out of the eleven chippers tested (see Figures A1 to A11). This is sufficient to distort the noise emission results, on some machines.

6.2.4 Changes to noise test code

It is clear that the wood defined by the standard noise test code does not behave the same as wood more typical of normal working within the infeed hopper. An alternative such as a trimmed log of hard or soft wood, with a length and thickness within certain tolerances could be considered as an alternative that could give an estimate of the realistic maximum noise emission.

The current standard takes the average of the first three consecutive results that are within 2dB. Where there is a large variation in level this choice of values is haphazard. An averaged result over several infeed cycles would be a more representative result.

6.3 QUIET MACHINES

Woodcchippers A and D proved to be the quietest machines. Both these machines gave sound pressure levels with normal wood below 100dB(A) at the operator position. Woodchipper A is a woodfuel chipper that was operated at a mid infeed speed and had a different cutting action to the other machines. These factors may account for this machine being quieter. Woodchipper D was operated at the maximum infeed speed and had the same cutting action as the other machines. The noise controls added to woodchipper D are clearly beneficial, and the result confirms that there is potential for reducing the noise emission and operator exposure of other woodchippers.

Woodchipper G is specified as having noise damping provided by a paint finish. This machine was not noted as being particularly quiet.

The highest noise levels for the operator were obtained from the tracked and road tow versions of woodchipper C. It is thought that noise control at the infeed hopper could reduce operator exposure.

6.4 OPERATOR HEARING PROTECTION

Noise control is the first priority where there is a risk of excessive noise exposure from wood-chipping operations; the most obvious control is the use of quiet chippers. The results here confirm that quieter woodchippers can be produced however it is likely that hearing protection will still be required.

Woodchippers should be designated as hearing protection zones where use of hearing protection is compulsory. Protectors should provide sufficient attenuation to prevent the daily exposure

15

6.5

exceeding 85dB(A). All machines have a generally broadband noise spectrum. Hearing protection with an SNR value of 30dB would be recommended. Hearing protection with an SNR value of 25 to 30dB would be adequate for operators of woodchippers A and D.

MANUFACTURERS’ NOISE DATA

Noise emission data for the machines tested was not seen in any printed or on line advertising.

Sound power and operator sound pressure level data in accordance with BS EN 13525:2005 was available for woodchipper J from the manufacturer; the UK and European suppliers did not have this data. The emission data supplied was comparable with the results reported here.

The manufacturer of woodchippers B and C supply data and test details within the handbook and label their machines with the sound power and the sound pressure level at 10m. Their test method is not in accordance with BS EN 13525:2005, but gives results comparable to the simulated real world data reported here. The manufacturer’s results are 4 to 5dB below the results given by the simulated standard test.

The manufacturers of woodchippers D, E, F, G and H labelled their machines with a sound power value but information on the operating conditions applicable to the value was not available.

The manufacturers’sound power values for woodchippers G and H are an underestimate of the noise emission compared to both the simulated real use and standard test condition results reported here.

It is a legal duty under the Supply of Machinery (Safety) Regulations 1992 for manufacturers/ suppliers to provide information on the noise emitted and the operating conditions applicable to the result. Not all manufacturers and suppliers are complying with this duty.

16

7 CONCLUSIONS

Noise levels for the operator can reach 107dB(A) but the prototype woodchipper D achieved levels below 99dB(A) by using additional noise controls. This machine has demonstrated the practicality of available noise controls for utility type woodchippers and HSE should encourage all other manufacturers to adopt these noise reduction measures, as required by the Supply Regulations. Noise exposure control by selection of quiet machines, and reduction of operator exposure time should be a priority rather than total reliance on hearing protection.

In general the noise emission is lower for untrimmed wood with soft branches. It is thought that this variation arises from the cushioning of impacts within the hopper.

Machines with dominant noise emission in the direction of the hopper and possibly also with a large variation in noise emission with material type are those most likely to benefit from noise damping of the hopper (to reduce the noise from impacts) or change of hopper design (to reduce the number of impacts). Noise control at the hopper would be of direct benefit to the operator, providing a reduction in noise exposure.

The 12mm square cut standard wood in 4m lengths specified in the BS EN 13525:2005 noise test code gives significantly increased noise at high frequencies in the hopper direction on most machines. This high frequency noise often dominates over the normal operating noise. This could cause problems when rank ordering machines in terms of sound power or operator noise exposure. Consideration should be given to use of a wood that gives less distortion of the noise characteristics of the chipper.

Ideally the standard noise test code should use longer measurement periods averaged over repeated cycles.

Manufacturers and suppliers are not consistently providing noise emission data. All manufacturers need to declare the sound power and the operator sound pressure level for conditions typical of normal use, including the worst case, as required by the Supply Regulations. This may be done using the noise test code in BS EN 13525:2005, or by an alternative method that must be specified.

Hearing protection is required even with the quietest woodchippers and woodchippers should be designated a hearing protection zone. Woodchippers have a generally broadband noise spectrum. Hearing protection with an SNR value of 30dB or more should be used. An SNR value of 25 to 30dB would be adequate for the quieter woodchippers A and D.

17

8 RECOMMENDATIONS

The prototype woodchipper D demonstrated that significant reductions in noise emission are possible. All new woodchippers should be manufactured with similar noise controls under the requirements of the Supply of Machinery (Safety) Regulations 1992.

For users to select quiet machines manufacturers and suppliers must supply noise emission and operator sound pressure level information as required under the Supply of Machinery (Safety) Regulations 1992. HSE should encourage all manufacturers and suppliers to make this information readily available to prospective customers.

The noise test code in BS EN 13525:2005 should be improved. The requirement to report the first three chipping cycles within 2dB increases the uncertainty in the measured noise emission and operator sound pressure level. The measurement should instead be made over several cycles of chipping providing a measurement period of at least one minute. Consideration should also be given to a different wood. The 50mm square cut wood specified by the noise test code can cause significant additional high frequency noise in the hopper direction. A thicker more rigid wood would possibly give a more typical noise emission.

Impacts of the wood with the hopper can be the dominant noise from a chipper. Machines that show a strongly directional noise from the hopper side and also larger variations of noise emission between trimmed and untrimmed wood are possibly more susceptible. Damping applied to the outside of the hopper may reduce the noise from impacts; change of hopper shape may reduce the number of impacts.

18

9 REFERENCES

British standard BS EN 13525:2005 Forestry machinery - Wood chippers – Safety

British standard BS EN ISO 12100-1:2003 Safety of machinery – Basic concepts, general principles for design - Part 1: Basic terminology, methodology.

Health and Safety Executive Controlling Noise at Work – The Control of Noise at Work Regulations 2005 Guidance on the regulations L108

Statutory Instruments The Noise Emission in the Environment by Equipment for Use Outdoors Regulations 2001 amended by The Noise Emission in the Environment by Equipment for Use Outdoors (Amendment) Regulations 2001

Statutory Instrument The Supply of Machinery (Safety) Regulations 1992

19

10 APPENDIX A FREQUENCY SPECTRA

The following figures show the third octave band frequency spectra measured with the B&K 2260 sound level meter/ analyser at Position 1 (facing and slightly off centre to the hopper of each chipper). The sound pressure level recorded is the unweighted Leq in each third octave band.

55

60

65

70

75

80

85

90

16 25 40 63 1k 4k

B

id

id id

Woodchipper A mid and maximum infeed speed

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k

Third octave band centre frequency Hz

Soun

d pr

essu

re le

vel d

Trimmed softwood mid Untrimmed softwood mid Trimmed hardwood m

Untrimmed hardwood m Standard m Standard max

Figure A1 Noise spectra measured 7m from centre of woodchipper A

This woodchipper was run at the mid infeed speed when chipping the trimmed and untrimmed hard and soft wood. Measurements were made at both mid and maximum infeed speed when chipping the wood simulating the standard test conditions.

20

55

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

Woodchipper B maximum infeed speed

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Soun

d pr

essu

re le

vel d

B

Trimmed softwood Untrimmed softwood Trimmed hardwood

Untrimmed hardwood Standard

Figure A2 Noise spectra measured 6.5m from centre of woodchipper B

21

50

55

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

Woodchipper C tracked version maximum infeed speed

100

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB



Figure A3 Noise spectra measured 7.5m from centre of tracked version of woodchipper C

22

50

55

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

i

Woodchipper C road tow version maximum infeed speed

100

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB

Trimmed softwood Untrimmed softwood Tr mmed hardwood


Figure A4 Noise spectra measured 7m from centre of road tow version of woodchipper C.

23

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

i

Woodchipper D maximum infeed speed

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB

Trimmed softwood Untrimmed softwood Tr mmed hardwood


Figure A5 Noise spectra measured 7.5m from centre of woodchipper D

24

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

Woodchipper E maximum infeed speed

100

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k

Thrid octave band centre frequency Hz

Soun

d pr

essu

re le

vel d

B



Figure A6 Noise spectra measured 7.5m from centre of woodchipper E

25

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

Woodchipper F maximum infeed speed

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB



Figure A7 Noise spectra measured 7.5m from centre of woodchipper F

26

60

65

70

75

80

85

90

95 16 25 40 63 1k 4k

Woodchipper G maximum infeed speed

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB



Figure A8 Noise spectra measured 7.5m from centre of woodchipper G

27

65

70

75

80

85

90

95

16 25 40 63 1k 4k

Woodchipper H maximum infeed speed

100

100

160

250

400

630

1.6

k

2.5

k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB



Figure A9 Noise spectra measured 7.5m from centre of woodchipper H

28

60

65

70

75

80

85

90

95

100

16 25 40 63 100

160

250

400

630

i

id

Woodchipper I mid and maximum infeed speeds

1k

1.6

k

2.5

k

4k

6.3

k

10k


Soun

d pr

essu

re le

vel d

B

Trimmed softwood max Untrimmed softwood max Tr mmed hardwood max

Untrimmed hardwood max Standard max Standard m

Figure A10 Noise spectra measured 7.5m from centre of woodchipper I

Measurements during chipping of trimmed and untrimmed logs made with chipper operating at maximum infeed speed (PTO 1000rpm). Measurements with standard wood at max infeed speed and repeated at mid infeed speed (PTO 540rpm).

29

65

70

75

80

85

90

95 16 25 40 63 10

0

160

250

400

630

Woodchipper J maximum infeed speed

1k

1.6

k

2.5

k

4k

6.3

k

10k


Sou

nd p

ress

ure

leve

l dB



Figure A11 Noise spectra measured 7.5m from centre of woodchipper J

30

11 APPENDIX B – CHIPPER PHOTOGRAPHS

Woodchipper A

31

Woodchipper B

32

Woodchipper C tracked version

33

Woodchipper C Road tow version

34

Woodchipper D (prototype with additional noise controls)

35

Woodchipper E

36

Woodchipper F

37

Woodchipper G

38

Woodchipper H

39

Woodchipper I

40

Woodchipper J

41

12 GLOSSARY

A-weighting A weighting of the audible frequencies designed to reflect the response of the human ear to noise. The ear is more sensitive to noise at frequencies in the middle of the audible range than it is to either very high or very low frequencies. Noise measurements are often A-weighted (using a dedicated filter) to compensate for the sensitivity of the ear. In this report A-weighted decibel levels are indicated as dB(A).

Attenuation Noise reduction, measured in decibels.

C-weighting A weighting of the audible frequencies often used for measurement of peak sound pressure level. The A-weighting is not appropriate at very high noise levels; as the noise level increases the ear is better able hear low and high frequency. C-weighting has an almost flat (or linear) response across the audible frequency range.

Cycle An operation or sequence of operations (of a machine) which is repeated. For the wood chipper a cycle was the period between the start of infeeding a piece of wood, to the start of infeeding of the next piece.

Daily personal noise exposure (LEP,d) A measure of the average noise energy a person is exposed to during a working day. The LEP,d is directly related to the risk of hearing damage.

Decibel dB The units of sound level and noise exposure measurement.

Dosemeter An instrument designed to continuously measure noise exposure when worn by a person during their normal daily work.

Equivalent continuous sound pressure level (Leq) A measure of the average sound pressure level during a period of time, in dB.

Frequency (Hz) The pitch of the sound, measured in Hertz.

Frequency analysis Analysis of a sound into its frequency components to give the noise spectrum.

Infeed Wood feed into the chipper for chipping, or the action of feeding wood for chipping.

LEP,d (see daily personal noise exposure)

Leq (see equivalent continuous sound pressure level)

Octave-bands A division of the frequency range into bands, the upper frequency limit of each band being twice the lower frequency limit.

Third octave band Single octave-bands divided into three parts.

Peak sound pressure level The maximum value reached by the sound pressure at any instant during a measurement period in dB.

Sound level meter Instrument for measuring various noise parameters.

SNR (single number rating) A method of estimating the attenuation of ear protection based on a single parameter given by the ear protection manufacturer.

42

Sound power level A measure of the total acoustic power produced by a noise source.

Sound pressure level The basic measure of noise loudness, expressed in decibels, usually measured with an appropriate frequency weighting.

43

Published by the Health and Safety Executive 07/08





The Health and Safety Laboratory performed measurements of the noise emission and operator noise exposure of a range of mobile, hand fed, wood chippers under simulated standard and real world operating conditions. These measurements were made on behalf of the Forestry Commission and Jason Liggins of the Health and Safety Executive’s Policy Group - Agriculture and Food Section.






This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

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