Noise emissions and exposure from mobile woodchippers - HSE

Health and Safety
Executive
Noise emissions and exposure from
mobile woodchippers
Prepared by Health and Safety Laboratory
for the Health and Safety Executive 2008
RR618
Research Report

Health and Safety
Executive
Noise emissions and exposure from
mobile woodchippers
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
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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 1BQ
or by e-mail to hmsolicensing@cabinet-office.x.gsi.gov.uk
ii

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.
iii

CONTENTS
1 INTRODUCTION......................................................................................... 1
2 LEGAL DUTIES FOR MANUFACTURERS AND SUPPLIERS, AND
STANDARDS FOR WOODCHIPPERS ............................................................. 2
2.1 Noise control............................................................................................ 2
2.2 Noise test code ........................................................................................ 3
3 SELECTION OF WOOD CHIPPERS FOR USE IN THE STUDY ............... 4
4 MEASUREMENT PROCEDURE ................................................................ 6
4.1 Operating conditions................................................................................ 6
4.2 Measurement conditions.......................................................................... 6
5 RESULTS ................................................................................................... 8
5.1 Sound power results ................................................................................ 8
5.2 Operator position sound pressure level ................................................. 10
5.3 Frequency content of the chipper noise................................................. 12
5.4 Direction of the chipper noise ................................................................ 12
5.5 Half length timber in standard test ......................................................... 12
5.6 Manufacturer’s Data .............................................................................. 13
6 MATTERS RAISED BY THE RESULTS................................................... 14
6.1 Possible impacts WITH HOPPER ......................................................... 14
6.2 Suitability of noise test code .................................................................. 14
6.3 Quiet machines...................................................................................... 15
6.4 Operator hearing protection................................................................... 15
6.5 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
v

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

viii

1 INTRODUCTION
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.
1

2.1
2
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 designing
low-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.
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:
2.2
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.
3

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.
4

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
F Tracked 50hp diesel
engine
G Road tow 34hp diesel
engine
H Tracked 50hp diesel
engine
I Wood fuel PTO 1000 rpm
(Valtra 6550)
J Road Tow 28hp diesel
engine
Discblades
Discblades
6 90º 4
7 90º 4
Disc 6 90º 2
Disc 9 90º 2
Disc 10 45º 2
Disc 6 90º 2
5

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.
6

1
Infeed
hopper
operator
discharge
4 3
Figure 1 Approximate measurement positions around chipper
CEL 360 noise dosemeters at each measurement position recorded the A-weighted Leq, and Cweighted
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.
7
2

5.1
SOUND POWER RESULTS
5 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 (10 Lw1/10 + 10 Lw2/10 +10 Lw3/10 +10 Lw4/10 )/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.
8

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
with added noise
controls
113.5 0.5 112.5 1.1 114 0.9 110.5 0.3 117.5 1.0
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.
9

5.2
Sound power dB(A
130
125
120
115
110
105
100
A
B
C tracked
C road tow
D
E
Chipper
F
Figure 2 Noise emission of wood chippers
OPERATOR POSITION SOUND PRESSURE LEVEL
G
H
I
J
Trimmed softwood
Untrimmed softwood
Trimmed hardwood
Untrimmed hardwood
Standard
The operator’s noise exposure has been taken from the dosemeter worn on the shoulder. The Aweighted
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.
Sound pressure level dB(A
115
110
105
100
95
90
85
A
B
C tracked
C road tow
D
E
Chipper
F
Figure 3 Sound pressure level measured on operator
10
G
H
I
J
Trimmed softwood
Untrimmed softwood
Trimmed hardwood
Untrimmed hardwood
Standard

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.
ID Type Trimmed
softwood
Overall
A Wood
fuel
PTO
Table 4 Operator position sound pressure level dB(A)
Leq
30s
Leq
spread
Untrimmed
softwood
Overall 30s
Leq
Leq
spread
Trimmed
hardwood
Overall 30s
Leq
Leq
spread
Untrimmed
hardwood
Overall 30s
Leq
Leq
spread
100 2 96.5 1 100 1 97 1 99
max
99.5
mid
Standard
wood
Mean Std
Leq dev
of
three
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
D Road
tow
prototype
with
added
noise
controls
E Road
tow
106 1 101 2.5 107.5 0 105 1.5 109 0.5
99 1 97.5 3 99 0 96 1 102 0.8
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
J Road
Tow
102.5 1.5 100 1.5 104.5 2 101.5 0 100
max
1.6
94.5
mid
0.4
104 0.5 105 5 104 0.5 101 2 98.5 1.2
11
3.8
2.1

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
D Road tow prototype
with added noise
controls
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
5.5
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
12

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.
5.6
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)
A Wood fuel
PTO
Not
available
Operator
sound
pressure
level dB(A)
Not
available
B PTO 115 Not
available
C Tracked 119 Not
available
C Road tow 119 Not
available
D Road tow
prototype with
added noise
controls
Labelled
as 91
E Road tow Not
available
Not
available
Not
available
F Tracked 120 Not
available
G Road tow 115 Not
available
H Tracked 114 Not
available
I Wood fuel
PTO
Comments
The supplier had no data and had requested data from
this trial
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.
Contacted manufacturer by e-mail for data. No
information on operating conditions supplied.
Supplier had no further information on operating
conditions. No response from manufacturer.
Supplier had no information on operating conditions
for labelled sound power. Contacted importer for
further information, and had no response.
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.
13

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.
14

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 woodchipping
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

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.
6.5
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

British standard BS EN 13525:2005
Forestry machinery - Wood chippers – Safety
9 REFERENCES
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.
Sound pressure level dB
90
85
80
75
70
65
60
55
16
25
40
63
Woodchipper A mid and maximum infeed speed
100
160
250
400
Trimmed softwood mid Untrimmed softwood mid Trimmed hardwood mid
Untrimmed hardwood mid Standard mid Standard max
630
1k
1.6k
Third octave band centre frequency Hz
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
2.5k
4k
6.3k
10k

Sound pressure level dB
95
90
85
80
75
70
65
60
55
16
25
40
63
Woodchipper B maximum infeed speed
100
160
250
400
630
1k
1.6k
Third octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A2 Noise spectra measured 6.5m from centre of woodchipper B
21
2.5k
4k
6.3k
10k

Sound pressure level dB
100
95
90
85
80
75
70
65
60
55
50
16
25
40
Woodchipper C tracked version maximum infeed speed
63
100
160
250
400
630
1k
1.6k
Third octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A3 Noise spectra measured 7.5m from centre of tracked version of
woodchipper C
22
2.5k
4k
6.3k
10k

Sound pressure level dB
100
95
90
85
80
75
70
65
60
55
50
16
25
40
Woodchipper C road tow version maximum infeed speed
63
100
160
250
400
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
630
1k
1.6k
Third octave band centre frequency Hz
Figure A4 Noise spectra measured 7m from centre of road tow version of
woodchipper C.
23
2.5k
4k
6.3k
10k

Sound pressure level dB
95
90
85
80
75
70
65
60
16
25
40
63
Woodchipper D maximum infeed speed
100
160
250
400
Trimmed softwood Untrimmed softwood Trimmed hardwood
630
1k
1.6k
Third octave band centre frequency Hz
Untrimmed hardwood Standard
Figure A5 Noise spectra measured 7.5m from centre of woodchipper D
24
2.5k
4k
6.3k
10k

Sound pressure level dB
100
95
90
85
80
75
70
65
60
16
25
40
63
Woodchipper E maximum infeed speed
100
160
250
400
630
1k
1.6k
Thrid octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A6 Noise spectra measured 7.5m from centre of woodchipper E
25
2.5k
4k
6.3k
10k

Sound pressure level dB
95
90
85
80
75
70
65
60
16
25
40
63
Woodchipper F maximum infeed speed
100
160
250
400
630
1k
1.6k
Thrid octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A7 Noise spectra measured 7.5m from centre of woodchipper F
26
2.5k
4k
6.3k
10k

Sound pressure level dB
95
90
85
80
75
70
65
60
16
25
40
63
Woodchipper G maximum infeed speed
100
160
250
400
630
1k
1.6k
Thrid octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A8 Noise spectra measured 7.5m from centre of woodchipper G
27
2.5k
4k
6.3k
10k

Sound pressure level dB
100
95
90
85
80
75
70
65
16
25
40
63
Woodchipper H maximum infeed speed
100
160
250
400
630
1k
1.6k
Thrid octave band centre frequency Hz
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A9 Noise spectra measured 7.5m from centre of woodchipper H
28
2.5k
4k
6.3k
10k

Sound pressure level dB
100
95
90
85
80
75
70
65
60
16
25
Woodchipper I mid and maximum infeed speeds
40
63
100
160
250
Trimmed softwood max Untrimmed softwood max Trimmed hardwood max
Untrimmed hardwood max Standard max Standard mid
400
630
1k
1.6k
Third octave band centre frequency Hz
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
2.5k
4k
6.3k
10k

Sound pressure level dB
95
90
85
80
75
70
65
16
25
40
Woodchipper J maximum infeed speed
63
100
160
250
400
630
1k
1.6k
Third octave band centre frequency Hz
2.5k
4k
Trimmed softwood Untrimmed softwood Trimmed hardwood
Untrimmed hardwood Standard
Figure A11 Noise spectra measured 7.5m from centre of woodchipper J
30
6.3k
10k

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

Health and Safety
Executive
Noise emissions and exposure from
mobile woodchippers
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.
RR618
www.hse.gov.uk