B6 Ollie Flashcards
Noise
Noise at WorkRegulations 2005:
Any audible sound
Oxford English Dictionary:
A sound, especially one that is loud or unpleasant or that causes disturbance
Sound:
Vibrations or pressure changes passing through a medium, usually air
Sound
Amlitude- Strength in which sound travels
Frequency - Number of wave fronts hitting the ear drum
Time
Sound Intensity and Decibels
Intensity is sound power per unit area
A measure of the flow of sound energy - units W/m2 Lowest value detected by human ear is 10-12 W/m2 Highest likely to be encountered is 1 W/m2
Very large range so Decibel (dB) used for convenience Logarithmic scale
Usually express ed as sound pressure level
Decibel Scale
Threshold of pain -
130 Noisy factory - 90 Busy traffic - 70
Normal conversation -60 Soft whisper - 20
Threshold of hearing - 0
Logarithmic scale, so increase of 3 dB means doubling of sound intensity
Adding Decibels
If adding similar values , add 3dB
e.g. 90dB + 90 dB = 93dB
If adding dissimilar values , use graph or table
Frequency
Pitch of note
Sounds us ally a mixture of frequencies
Human hearing range given as 20Hz to 20KHz
Frequencies often divided into octave bands ,
represented by central value
Frequency important in control, and selection of hearing defenders
Frequency-Octave bands
Graph- dB vertical and Hertz (Hz) Horizontal
A-Weighting
Tones of the same pressure level do not sound equally loud to the ear, nor do they have the same potential for causing hearing loss
High frequencies sound louder and are more likely to cause damage
Low frequencies sound quieter and are less likely to cause damage
A- weighting compensates for this difference After A-weighting is adopted - dB(A)
C-Weighting
A-weighting is not appropriate at high noise levels
Ear becomes better at hearing high/low frequencies Almost linear response
Used for peak values -dB(C)
Noise Dose
Noise measurements usually averaged over a time period
Known as Leq:
L can be any length of time
Control of Noise at Work Regulations refer to Daily noise exposure:
Averaged over 8 hour period
Known as daily noise exposure or LEP,d
Also make reference to peak values
Mechanism of Hearing
Vibrations directed by pinna into auditory canal
Eardrum vibrates
Vibrations carried across middle ear by ossicles to cochlea
Vibrations pass through fluid in cochlea in inner ear Detected by sensory hairs (stereocilia)
Conveyed to brain by auditory nerve
Noise-AdverseHealth Effects
Nuisance and stress
Tinnitus
Noise induced hearing loss (NIHL)
Temporary threshold shift - reversible damage (auditory fatigue)
Permanent threshold shift - failure of her cells to
respond to frequencies
Acoustic trauma
TTS & PTS (NIHL) generally occurs in the 4000hz octave band- 4K dip
Acoustic Shock
Sudden, unexpected loud sound through headset May be below Action Values
No loss of hearing
Symptoms:
Early: tinnitus , dizziness , nausea
Intermediate: headaches , fatigue, anxiety
Late: hypersensitivity, anxiety returning to telephone work
Controls: Protection devices Reduce background noise Prompt repair of equipment Manual control of voice levels
Audiometry - Basic Principles
Routine health surveillance
Health surveillance required if risk assessment identifies risk to health
Guidance suggests this is regular exposure above upper exposure action value
Shall include test of hearing –audiometry
Used as base line assessment
Also implications in Civil Law
Audiometry - Method
Details given in s tandard (EN26189:1991)
Quiet environment
No significant noise for 16 hours previously
Pure tones played - subject presses button if heard Software produces graph (audiogram)
Audiometry - Action to be Taken
Category& Action
1: Acceptable:
No action required
2: Mild hearing impairment:
Formal notification
Reinforcement of training and importance of controls Good practice to issue copy of audiogram
3:Poor hearing:
Referral to medical practitioner
4: Rapid hearing loss
Referral to medical practitioner
Control of Noise at Work Regulations (CNWR)2005-Regulation 4 & 5
Reg.4:
Exposure action values and exposure limit values
Reg.5:
Assessment to be carried out where exposure likely to reach lower exposure action value (80 dB(A))
To cover: Level, type, duration of exposure Manufacturers information Availability of alternative equipment Results of health surveillance Availability of PPE Recorded and reviewed
CNWR -Action Values
Lower Exposure Action Value - 80 dB ( A )
LEP,d / Peak 135 dB ( C ) :
Make PPE available
Provide information and training Assessment Upper Exposure Action Value -85dB(A)
LEP,d/Peak137 dB(C):
Reduce ALARP by means other than PPE
Hearing Protection Zones
Health surveillance (audiometry)
CNWR - Limit Values
Upper Exposure Limit Value - 87 dB ( A ) LEP , d / Peak 140 dB ( C ) :
Not to be exceeded
CNWR - Limit Values Exceeded
Exposure is not permitted above exposure limit value (87dB(A))
If exposure does occur, employer must reduce
exposure to noise to below the exposure limit value
Identify the reason for that exposure limit value being exceeded
Modify the organisational and technical measures to prevent it being exceeded again
CNWR -Regulation 7
Hearing protection:
To be made available at or above lower exposure action value
Must be worn above upper exposure action value (if cannot be controlled by other means )
Hearing Protection Zones:
Designated and signage displayed
Employer to maintain PPE and ensure use SFARP (Reg 8)
CNWR -Regulation 9 & 10
Reg.9 -Health surveillance:
Where the risk assessment indicates that there is a risk to health Risk to health:
If there is regular exposure above the upper exposure action value
Must include a hearing test (audiometry)
If hearing damage is identified then the employer must refer the individual to a medical practitioner.
Reg. 10:
Employer to provide information, instruction and training where lower exposure action value is reached
CNWR -Employees Duties
To comply with the employers arrangements for controlling noise
To use hearing protectors and noise control equipment
To take care of such equipment, and to report any defects (all Reg 8)
To co-operate with employer and attend hearing tests (Reg 9)
Noise Measurement - Basic Principles
Sound Level Meter:
Simple measures dB or dB(A) at a moment in time Integrating if measures Leq
Leq - equivalent continuous noise level
Need to measure A-weighted Leq (LAeq)
Need C-weighting for peak levels
Need to be calibrated each time they are used
Noise Measurement-Classes of Device
Lower the class of SLM, higher the quality
Class 0-Research
Clas s 1 - Laboratory/Field
Class 2 -General Field
Class 3-Non integrating
Calibrators also different classes
Selection depends on objectives of survey
Increasing accuracy and response from
Class 3 toClass 0
Class 1 or 2 for occupational safety measurements
Noise Measurement - Personal Dose Meters & Frequency Analysers
Personal dose meters:
Worn by person exposed in hearing zone
Measures actual dose for referenced time period
Frequency analysers:
Measure sound pressure levels at particular frequencies
Required for accurate assessment of hearing defenders
Combination of above and accessories
e.g. storage of data, print outs , software
Work place Noise Survey
Planning:
Objectives and scope
Information sources: Previous assessments Employees Manufacturers information Complaints Selection of measuring equipment including calibrators Battery check Number of employees exposed/duration Areas to be surveyed Recording of data Route Safety issues/risk assessment
The Ready Reckoner - Estimate (L108)
Estimate of noise exposure:
Try this :
1) 30mins spent working on a grinding machine - manufacturers info says 95dB
2) 3hours working in yard with vehicles - check
suggests 85dB
3)1.5hours in office-check suggests 80dB
4 ) 2 hours back in yard at 85d B
Estimating LEPd - Static Measurements
Static measurements taken at operating positions at each machine
Static measurements taken during normal operation
Sound measured as LAeq
Use integrating SLM
Note the time operator spends at each machine
Calculate using points system/HSE s preadsheet
Assess or assume insignificant exposure during breaks
Noise Propagation
Walls-Screens–steel Cladding
Effect of Distance - Inverse Square Law
Inverse square law:
Refers to decrease in noise energy (and other energy forms ) as it moves away from a point source
Energy/intensity is proportional to 1/d2* (d = dis tance)
At 1 unit distance = 1/1 2* = 1
At 2 units distance=1/22=1/4
At 3 units distance=1/32=1/9
Note: 2*denotes squared
Effect of Distance - Doubling Distance
Doubling of distance means a reduction of noise of 6 dB
Controlling Noise-General Principles
Eliminate at source, or control so far as is reasonably practicable at source (e.g. by relocation, redesign and maintenance)
Control along the transmission path (e.g. by using
isolation, barriers and enclosures)
Control exposure at the receiver (e.g. by enclosures , acoustic havens , hearing protection zones and PPE, limiting exposure time, audiometry)
Controlling Noise-Methods (1)
Engineering controls
Selection of equipment (presses instead of hammers ) Location of pipe-work and ducting
Reduce operation speeds
Distance/orientation
Maintenance (balancing, sharpening, tightening)
Controlling Noise-Methods (2)
Enclosure (noise enclosures ) Isolation(noise havens,springs to absorb energy)
Silencers (air movements /absorptive reactive)
Lagging
Damping (pads,stiffening)
Screens
Absorption
PPE
Acoustic Enclosure - Design (1)
Keeps noise in Heavy outer wall (plasterboard and brickwork) Inner lining of acoustically absorbent material Absorbent covered in protective mesh Flexible pipes to form vibration breaks Services in through ground Inspection door double/triple glazed Access panels for maintenance
Acoustic Enclosure - Design (2)
Access doors air tight Any joints to outside sealed Motors on dampers Machines covered in enclosures Avoid contact between equipment and walls Sound absorbent material on floors Silencers on any ventilation exits Self-closing doors Exterior controls
Acoustic Haven
Keep noise out Air conditioned/lighting/thermal comfort/works stations Viewing windows Emergency response (fire alarms etc) Above workplace for better view External surface reflective Internal acoustic absorbent Internal walls cleanable Isolated from floor and ceiling Double/triple glazed Air supply through lagged pipework
Hearing Protection - Basics Principles (1)
Selection is critical Matched to noise characteristics Will only be effective when used Types and specifications: Ear defenders Semi-inserts Earplugs Active hearing protection
Hearing Protection - Basics Principles (2)
Mean attenuation values at frequency bands
63-8000 Hz
Subjective tes t - 16 test subjects
Standard deviation values for each (+/-84%)
Assumed protection values at each frequency ( = mean – one standard deviation)
HML (high, medium, low) values SNR (single number rating)
Hearing Protection - Selection
Use HML (apply formula)
Use SNR
Octave band frequency
Hearing Protection - Single Number Rating (SNR)
Simple guide to hearing protection required:
Noise Level dB(A)&SNR Required
85-90-20or less
90-95- 20-30
95-100 - 25-35
100-105- 30 or more
Vibration - Basic Principles
Oscillating movement of a fixed point due to applied energy
Vibration - Basic Terms
Displacement (amplitude) – maximum distance moved from the point of oscillation
Frequency – number of complete oscillations per
second (Hertz )
Velocity – speed of the oscillating object at a fixed point in time (m/s ) Acceleration – maximum rate of increase in s peed (m/s 2 )
Magnitude – Vibration at Work Regulations 2005= acceleration
Measurement of Vibration
Accelerometer
Average (root-mean-s quare) of acceleration in three planes
Weighting given to most harmful frequencies (8-20Hz) Expressed as A(8)-daily exposure
Hand Arm Vibration Syndrome (HAVS)
Impaired circulation to fingers - blanching (white finger) Numbness in fingers , reduced sensitivity, tingling
Loss of dexterity
Loss of grip strength
Pain (especially in cold weather)
Infection/gangrene
Carpal Tunnel Syndrome and associated symptoms
Whole Body Vibration
Range of health effects Back pain Nausea Gastrointestinal upsets General feeling of discomfort, including headaches Loss of equilibrium (balance) Abdominal pain
Factors Contributing to Risk
Damage depends on: Vibration magnitude Vibration frequency Duration of exposure Individual susceptibility (diabetics /smokers more at risk) External temperature Tightness of grip
Control of Vibration at Work Regulations (CVWR) 2005- EAVs & ELVs
Exposure limit values and exposure action values :
Hand-armvibration:
EAV 2.5ms -2 A(8)
ELV 5.0 ms -2 A(8)
Whole body vibration:
EAV 0.5ms -2 A(8)
ELV 1.15ms -2 A(8)
A(8) vibration dose averaged over an 8-hour shift
CVWR - ELV
Must not be exceeded
If exceeded then:
Reduce exposure to vibration to below the limit value
Identify the reason for that limit being exceeded
Modify the measures taken to ensure it does not happen again
CVWR - ELV
Provide appropriate health surveillance
(Regulation 7)
Provide adequate information, instruction and training (Regulation 8).
CVWR -Risk Assessment
Reg 5:
Risk assessment required if employees are exposed to risk due to vibration
Assessmentto consider:
The frequency and magnitude of vibration
The health effects of exposure to vibration
Any information provided by the manufacturers of work equipment
The availability of replacement equipment designed to reduce exposure to vibration
Specific working conditions such as low temperatures appropriate information obtained from health surveillance
Estimating Daily Exposure
Graph
Points system
Hand Arm Vibration - Controls
Automation Change of work method Modify/use alternative equipment Purchasing policy Maintenance Monitor exposure and enforce limits Job rotation Instruction and training Health surveillance PPE - gloves to keep hands warm Warm temperatures
Hand Arm Vibration - Health Surveillance
Tier 1 - A short questionnaire used for new workers
Tier 2 - A short questionnaire for employees already exposed
Tier 3 - This involves a HAVS health assessment by a qualified person, if the assessments hows that the employee has HAVS, Tier 4 will apply
Tier 4 - Formal diagnosis by occupational health
physician
Tier 5 - Optional: referral for further tests
Hand Arm Vibration - Tier 3/4 Assessment
Grip strength Muscular dexterity Vascular Finger rewarming after cold provocation Finger systolic blood pressure Sensorineural Vibrotactile perception threshold Thermal perception threshold
Hand Arm Vibration - Stockholm Workshop Scales
(Sensorineural)
Stage -Description:
0 SN - Vibration exposed & no symptoms
1 SN - Intermittent numbness with or without tingling
2 SN - Intermittent or persistent numbness , reduced
sensory perception
3 SN - Intermittent or persistent numbness , reduced tactile discrimination and/or manipulative dexterity
Hand Arm Vibration - Stockholm Works hop Scales
(Vascular)
Stage -Grade -Description:
0 - No grade - No attacks
1V - Mild - Occasional attacks affecting tips of one or more fingers
2V-Moderate-Occasional attacks affecting distal and middle(rarely also proximal) phalanges of one or more fingers
3V - Severe - Frequent attacks affecting all phalanges of most fingers
4V-Very severe-As in stage 3 with trophic skin changes in the fingertips
Whole Body Vibration - Controls
As for HAVS e.g. maintenance/automation etc
Specific examples:
Drive vehicles more slowly
Ergonomic design of vehicle cabs
Mount seats on springs or compression pads / provide cushions Provide rubber mats for standing tasks
