B6-NOISE AND VIBRATION Flashcards
A small engineering organisation operates a number of noisy machines that are located in an open plan workshop.
Following a noise survey the organisation discovers that its employees are being
exposed to noise levels above the upper exposure action value of 85 dB(A) LEPd.
Describe the range of technical control measures that could be taken to reduce the employees’ exposure to noise. (10)
the range of technical control measures that could have been introduced under the general
headings of those associated with the source, the transmission and the receiver.
Thus, for instance, they could have suggested replacing older and noisier equipment with
machines that emitted lower levels of noise;
reducing the speed of the machines;
mounting the noisy equipment on rubber strips or dampers;
applying damping to metal panels on machines;
fitting silencers on exhausts and metal ducting and ensuring the machinery was maintained on a regular basis.
As for noise transmission, appropriate
control measures would include the provision of a noise enclosure of suitable noise
attenuating material around the main sources of noise;
placing acoustic screens around noisy equipment;
and lining the walls and floor of the workshop with acoustically absorbing material.
Finally the exposure of noise to employees could be reduced by isolating the more noisy equipment in another area of the workshop and introducing automation and creating a noise haven for the employees.
As a very last resort, the additional use of hearing protection might have to be considered.
A noise survey is to be carried out in a large enclosed turbine hall within an electricity generating power station. In the turbine hall there are three steam driven turbines and other mechanical plant associated
with power generation.
Exposure to noise is a considerable problem for the 50 employees who work on each shift in the turbine hall, especially when all three turbines are running. Explain how a noise survey should be planned and undertaken in order to assess employees’ noise exposures in this workplace. (20)
The importance of providing information to and consulting with the workforce prior to the survey, using a competent assessor, considering all available relevant information
such as
previous surveys, existing controls, machinery manufacturers data, maintenance and
audiometry records and calibrating measuring equipment before and after
measurements were taken.
A suitable framework for the exercise could be based on a basic survey, a detailed survey and then a section on frequency analysis and
personal noise exposure.
A basic survey would involve the use of simple sound level meters or integrated sound
level meters to measure noise levels at planned points around the turbine hall.
This would enable identification of areas where noise exposure was at or above action
levels and would identify the main sources of noise. A record would have to be kept of
the machinery that was in operation when the survey was carried out.
The detailed survey would involve the use of integrated sound level meters.
A decision should be made on suitable sample times over which to measure Leq with the
measurement of noise levels being made at operator positions averaged over typical
time periods, a note made of the employees’ length of exposure, and a calculation
method such as a nonogram used to determine exposure (LEP,d).
The survey should include the measurement of peak noise levels with the results being plotted on a noise map.
Using the octave band frequency analysis function on the sound level meter,
measurements would have to be made of noise levels at each frequency band.
This would help in making decisions both on the noise control measures to be taken and
also on the selection of correct hearing protection.
As for personal noise exposure, dosimeters could be issued to a selection of operators and peripatetic workers to measure noise dose over a representative period of time.
The start and finish times of the exercise would have to be noted and care
taken to ensure that the microphone was positioned close to the ear.
This exercise would determine the actual LEP,d and LEP,w of the individuals concerned.
A small printing organisation operates a number of printing machines that are located in an open plan workshop.
Following a noise survey the organisation discovers that its employees are being exposed to noise levels of 86 dB(A) LEP,d.
(a) Outline the significance of this noise level to an employer. (5)
Noise level in workshop = 86dB(A) Lepd is above the CoNaWR EAV of 85 dB(A) Lepd but below the ELV of 87 dB(A) Lepd;
at 86dB(A) there is a risk of NIHL and consequent hearing damage;
this could affect insurance cover / liability and also result in enforcement action & civil claims;
so the employer must take steps to reduce noise level below 85dB(A) and ALARP.
A small printing organisation operates a number of printing machines that are located in an open plan workshop.
Following a noise survey the organisation discovers that its employees are being exposed to noise levels of 86 dB(A) LEP,d.
(b) Describe the range of technical AND organisational control measures that could be introduced. (15)
Technical measures:
elimination - discontinue noisy activity and/or change process (options likely to be limited);
purchase quieter machinery;
maintain machinery to reduce noise output;
re-locate machinery away from occupied areas;
barriers / screens / noise enclosures / havens;
anti-vibration mounts / springs / damping to reduce vibrational noise;
lining walls / ceilings with noise absorbent
materials;
hearing protection selected on basis of noise survey and octave band analysis.
Organisational measures:
job rotation / breaks;
training & information;
issue hearing protection & regular inspection;
supervision / enforcement
Explain what is meant by “threshold shift”. (2)
Threshold shift = reduction in a person’s sensitivity to sound often caused by high noise exposures.
Can be temporary (TTS) or permanent (PTS = NIHL);
TS is measured as the difference between the hearing threshold of a subject under test and that of a healthy young adult with no hearing impairment.
TS is measured as “hearing loss” in dB(A).
Outline the benefits and limitations of audiometry as part of a hearing conservation programme. (6)
The benefits of audiometry include:
- the provision of evidence of the effectiveness of a hearing conservation programme
- can identify susceptible individuals
- can be used at pre-employment medicals for identifying those with existing NIHL
• provides an opportunity to train & inform employees on the prevention of hearing loss
The limitations of audiometry are:
- it is reactive nature only identifies hearing damage after the event
- resource implications - cost, time, inconvenience
• it is dependent on reliable subject response, operator competence and avoidance of confounding factors (such as temporary threshold shift, tinnitus etc)
• the possibility of promoting claims by employees
• it cannot differentiate between NIHL caused by occupational and non-occupational exposures
Drivers of earth-moving machinery at a large construction site have reported incidences of back pain which they believe are caused by exposure to whole body vibration.
(a) Outline a range of control measures that could be used to minimise the risk of the drivers experiencing back pain caused by exposure to whole body vibration.(7)
Vehicle selection (power, stability, suitability for terrain) so as to minimise levels of vibration and ensure compliance with requirements in CoVaWR 05 - ref to exposure action / limit values;
provide designated routes avoiding rough / uneven surfaces where practical;
regular road / surface maintenance;
ensure padded, spring mounted seat, adjustable for weight / size of driver and with
adequate back support;
job rotation / breaks / task variation;
training / information on hazards / health
effects / control measures required - eg speeds / driving style etc; supervision
Drivers of earth-moving machinery at a large construction site have reported incidences of back pain which they believe are caused by exposure to whole body vibration.
(b) Suggest THREE other possible work-related causes of the back pain being experienced by these
drivers. (3)
Poor posture / driving position / badly adjusted seat position;
ergonomic issues - poor design /
layout of controls / obstructed visibility resulting in repeated stretching, bending, twisting etc;
lifting heavy tools and equipment / attachments;
repeated climbing into / jumping out of cab
The use of hand-held vibrating tools can cause hand-arm vibration syndrome (HAVS).
(a) Describe the health effects of HAVS. (4)
Firstly, vascular disorders (type A in list of Industrial Injuries), arising from damage to the capillaries carrying blood to the tissues; this results in reduced blood flow to the hands and particularly the fingers giving rise to characteristic symptoms that include intermittent blanching of the fingers (“white finger”), throbbing pain, chronic blanching / numbness / tingling - exacerbated in cold condition; and necrosis /
gangrene.
Secondly, peripheral sensori-neural disorders (type B), arising from damage to nerve tissues in the hand and fingers resulting in symptoms such as tingling, numbness, and loss of sensation / dexterity.
Thirdly, vibration exposure has also been associated with certain categories of bone and joint disorders (type C) and muscular disorders (type D) - ie musculoskeletal disorders / WRULDs such as Carpal
Tunnel syndrome - inflammation of the tendons (tendonitis) and joints in the wrist.
Other disorders (type E) such as those affecting the whole body and the central nervous system may also arise.
The use of hand-held vibrating tools can cause hand-arm vibration syndrome (HAVS).
(c) Outline a hierarchy of control measures that could be used to minimise the risks to employees of
developing HAVS when using such power tools. (8)
eliminate - eg use “wrecking ball” demolition instead of pneumatic drills
- mechanise - use JCB “nibbler” instead of drills
- use tools with appropriate power output (under-powered requires more time and effort)
- purchasing policy - low vibration tools
- change workstation design / ergonomic approach - postures / grip etc - eg jigs / holders
- maintenance regime - regular inspection and replacement of worn parts
- job rotation - rest periods
- provide warm clothing / PPE / heated handle grips
- health surveillance and occupational health support
- training (+ details of awareness, signs / symptoms and control measures)
+ ref to CoVaWR EAVs & ELVs
A machine operator is required to work at a number of different machines during a normal 8-hour
working day.
(a) Explain how a series of static measurements can be taken in the workplace and then used to
estimate the operator’s daily personal noise exposure (Lep,d). (5)
To obtain the operator’s Lep,d (daily personal noise dose / 8 hour time-weighted average noise exposure) take static measurements at the operating position for each machine during normal operation using an integrating sound level meter;
this will provide the individual LAeq,t, for each machine (L1, L2, L3 etc). The LEP,d value can then be obtained using a mathematical formula:
LEP,d = 10 Log
[(L1/10) + (L2/10) + (L3/10)…(Ln/10)].
Alternatively if the noise levels for the individual machines are measured, together with the duration of exposure at each machine HSE’s “nomogram” can be used to give a “fractional exposure” (f) value for
each machine / duration; the individual “f values” can then be added and converted into a daily personal noise dose Lepd in dB(A). The easiest way is to use the HSE noise calculator (on the HSE website) - simply input the individual static measurements and durations of exposure and the LEP,d is calculated automatically.
A machine operator is required to work at a number of different machines during a normal 8-hour
working day.
(b) The result of personal dosimetry on a similar day provides an Lep,d that is 4dB(A) higher than the
estimate made in (a). Identify the factors that may account for the difference. (5)
Differences may be due to:
- personal dosimetry is more accurate - gives a better estimation of actual exposure than static measurements; static measurements taken over too short a time / not representative
- change in work routine - spends longer at certain noisier machines
- uses different (noisier) work processes - different way of working / different materials / speeds
• change of circumstances - other contributory background noises present / greater levels of
reverberation / reflected sound from body
- using more sensitive equipment
- faults in calibration of devices
A&B Printing Ltd. operates a number of printing machines producing promotional magazines for the
retail trade.
They recognise that exposure to noise is a problem for all operatives within the open-plan print workshop and so the company plan to undertake a noise survey.
(a) Identify the different types of equipment that could be used to measure exposure to noise, making
reference to their respective features and roles in assessing noise exposure. (10)
Various types of equipment are used in measuring noise in the workplace - for example:
• sound pressure level meters - these come in a range of specifications the accuracy being
dependent on the level of sophistication; simple devices give a “real time” measurement of instantaneous sound pressure levels in dB(A) by measuring fluctuations in air pressure and
converting these to an analogue or digital readout. These are best suited to situations in
which the noise levels are reasonably constant
• integrating meters have the added feature that they can integrate the sound pressure levels of a period of time to give a time weighted average reading in dB(A) (Leq or Lepd). These are better suited to situations where there is significant fluctuation in noise levels. Some meters
are also capable of measuring peak noise values an applying other weighting factors eg
dB(C). More sophisticated devices can apply filters to obtain octave band analysis of the
noise; this enables measurement of the sound levels in particular frequency ranges. These
devices are generally used to take static or area measurements of noise in particular locations or around particular machines.
• personal noise dosimeters (dosimeters) are devices which are carried around by the worker
with the microphone attached to the lapel as a means of measuring personal noise dose over
a specific period. Personal noise meters give a more reliable and accurate measurement of a
person’s noise dose than can be achieved via static measurements, particularly where the
worker is peripatetic and subject to variable noise levels throughout the working day.
A&B Printing Ltd. operates a number of printing machines producing promotional magazines for the
retail trade.
They recognise that exposure to noise is a problem for all operatives within the open-plan print workshop and so the company plan to undertake a noise survey.
(b) Following the noise survey the company decide to fit an acoustic enclosure to one of the large
printing machines. Outline the design features of such an enclosure. (10)
An acoustic enclosure is a noise control measure designed to surround or enclose a noise source so as to keep noise inside the enclosure and prevent it affecting workers in the area.
Acoustic enclosures should be constructed of heavy duty materials such as double thickness brick or concrete covered externally by cladding or sheeting such as sheet steel.
Since brick and concrete have
poor sound absorbance properties they reflect sound thereby increasing sound levels within the enclosure and consequently increase the sound level transmitted to the outside. To counteract this, enclosures should also be lined with noise absorbent material to absorb reverberant noise and reduce
internal (and consequently external) noise levels.
Openings in enclosures - for example to allow
material to be fed into a machine - should be sealed with flexible rubberised “curtains” to reduce the level of noise that escapes or “leaks” out.
Vents and other openings should be sited so as not to point towards areas where workers are present.
Windows / observation panels should be double or triple glazed. Pipes or ducts leading from within the enclosure should contain flexible connectors to reduce
vibration transmission.
The enclosure should be sealed at floor level and machinery within mounted on
anti-vibration mounts / springs / dampers. Removable panels should be fitted to allow maintenance without entering the enclosure and to minimise noise levels during maintenance.
Since it is a heavy duty sealed construction, ventilation and heat build up may be a problem so it should be equipped with adequate ventilation ducts / fans etc and have measures for reducing heat build up.
A large open-plan print shop, employing 80 persons, operates several printing presses and includes associated activities such as photocopying, collating and packaging of printed materials.
Noise is considered to be a problem.
(a) Identify the information that should be obtained before undertaking a noise survey of the print shop. (6)
Information needed includes:
- Plan / layout of workshop
- type of building materials used (relevant because eg corrugated iron is highly reverberant)
- Number and types of noise sources – printing presses, packing machines, LEV, vehicles etc
- Manufacturer’s data on likely noise output
- Distribution of machinery in workshop
- Numbers employed / exposed; hours of work / shift patterns; duration of machine use
- Proximity to machinery
- Maintenance records
- Previous risk assessments
- Health records / results of health surveillance - audiometry
- Relevant legal requirements - CoNAWR 2005 and relevant thresholds
- Staff complaints / civil claims
- Details of existing control measures - enclosures / barriers / screens / sound-absorbent material PPE - assumed protection factor
A large open-plan print shop, employing 80 persons, operates several printing presses and includes associated activities such as photocopying, collating and packaging of printed materials.
Noise is considered to be a problem.
(b) Explain how the noise survey should be undertaken and describe the types of equipment that could
be used to assess employees’ noise exposures. (14)
Planning the survey: select a competent person to carry out the assessment;
provide information to
and consult with workforce beforehand;
review any relevant information available eg from previous surveys, data provided by machinery manufacturers, maintenance logs, complaints, enforcement
action, civil action, health surveillance / audiometry records;
draw up a plan of the workplace indicating
the positions of machinery and other key features such as any existing control measures and likely
occupancy levels.
Undertaking the survey: use a competent person(s);
use measurement devices / noise meters that meet approved design standards;
calibrate equipment before and after use using approved methods and equipment; apply a “staged” approach:
basic survey / detailed survey / frequency analysis / personal monitoring.
Basic survey: use a simple sound meter or integrating SLM to take measurements of sound pressure levels in dB(A) at various points around the plant so as to assess the general noise levels and identify
areas / activities where noise levels approach or exceed action levels set out in CoNaWR 05.
Keep records of noise levels and machinery in operation / work activities at time of the measurements.
Detailed survey: use of an integrating SLM; identify suitable measurement intervals;
take measurements at worker positions;
obtain readings of or calculate Leq and Lepd dB(A) measurements in order to assess whether action levels / exposure limits in CoNAWR are being exceeded.
Peak SPL measurements in dB(C) could also be taken for impact noise sources. Plot noise levels on plan of
workplace to obtain noise map / noise contours.
The octave band analysis function on SLM can be used to measure the frequency profile of the noise (ie SPL at each frequency band); this information assists in identifying the most effective means of providing noise control and in the selection of hearing protection.
Personal dosimetry involves a representative selection of machinery operators and peripatetic workers wearing noise dosimeters for a specified period of time.
The dosimeter consists of a microphone
positioned close to the ear and a meter records personal exposure levels (noise dose - as daily personal noise dose Lepd).
Drivers of tracked earth moving machinery at a large construction site have reported incidences of back pain which they believe are caused by exposure to whole body vibration.
(a) Outline a range of control measures that could be used to minimise the risk of the drivers experiencing back pain caused by
exposure to whole body vibration. (7)
Control measures that could be used to minimise the risk to drivers of tracked vehicles
from exposure to whole body vibration include selecting a vehicle with the size power
and capacity best suited for the terrain and task;
ensuring that an individual’s exposure
to whole body vibration is kept below the exposure limit value and preferably the
exposure action value;
organising traffic routes to avoid rough uneven surfaces wherever possible;
fitting suspension seats with vibration damping characteristics and adjusting these to suit the weight of individual drivers to avoid “bottoming out”;
organising work patterns including job rotation to ensure that drivers have breaks away
from the vehicle and advising them on how to minimise exposure to whole body
vibration by avoiding jolts and shocks
and
carrying out maintenance on a regular basis
on site roadways and the vehicles.
Drivers of tracked earth moving machinery at a large construction site have reported incidences of back pain which they believe are caused by exposure to whole body vibration.
(b) Outline THREE other possible work-related causes of the back
pain being experienced by these drivers. (3)
poor posture;
sitting for long periods of time;
the poor layout of controls requiring the driver to stretch and twist to reach a particular control or to obtain good vision;
no method provided for adjusting the seat which could make hand and foot controls difficult to operate;
the repeated climbing into and jumping down from a high cab and carrying out other construction related activities such as the manual handling of heavy loads.
A small printing company operates a number of printing machines which are located in an open plan workshop. Following a noise survey the company discovers that their employees are being exposed to noise
levels of 86dB(A) LEP,d.
(a) Outline the significance of this noise level to an employer. (5)
the quoted noise level of 86dB(A) LEP,d, whilst below the exposure limit value of 87dB(A)
LEP,d, was above the upper exposure action value of 85dB(A) LEP,d.
Consequently, the employer would need to reduce the exposure to a level as low as reasonably practicable by means other than hearing protection.
Failure to introduce the necessary
control measures could result in enforcement action being taken.
Additionally, long term exposure to the current noise level could cause damage to employees’ hearing which could possibly result in claims for noise induced hearing loss and increased
insurance premiums.
