06_physical_agents_1_noise_and_vibration_20140108083824

Question 1

wavelength

Answer 1

The wavelength (λ) determines the pitch of the sound. Wavelength is the length of one complete cycle, and is measured in metres (m). Its relationship to the frequency and speed of sound can be expressed as: Wavelength (λ) in metres = Speed of sound (c) / Frequency (f) Long, slow waves are a low pitch (like a fog horn). Short, fast waves are a high pitch (like a whistle).

Question 2

Frequency

Answer 2

Frequency (F) is the number of times a complete wave passes a point. It is measured in hertz (Hz), or cycles per second. The slowest, lowest sound a human can hear is approximately 20 Hz. The highest sound a human can hear is approximately 20,000 Hz (or 20 kilohertz - kHz).

Question 3

period

Answer 3

The period (T) is the time it takes to complete one full cycle, it is proportional to the frequency - T = 1/f (seconds).

Question 4

A-weighting:

Answer 4

 Reduces the importance of lower frequencies at 500 Hz or less. The lower the frequency, the greater the A-weighted correction factor becomes (see Figure 6.4).  Slightly increases the overall magnitude of the mid to high frequencies (2,000-4,000 Hz).  Reduces the very high frequencies as they extend beyond normal hearing.

Question 5

C-weighting:

Answer 5

Used principally for the evaluation of impulse noise and for hearing protection. It was originally intended to be used when measuring high sound pressure levels such as aircraft noise. C-weighted correction values show significantly less low frequency roll-off relative to the A-weighted correction values.

Question 6

The strength or loudness of a sound is determined by

Answer 6

the amplitude or height of the sound waves. Tall waves are loud; short waves are quiet.

Question 7

Amplitude is a convenient measure of the magnitude of the sound and can be related to its intensity and loudness and ultimately the effect it has on the human ear. There are various options for determining the amplitude: 3

Answer 7

 The peak value does not relate closely to the subjective impression of the sound.  An average value may be more appropriate but due to the symmetrical shape of the pressure wave positive sides of the wave ‘cancel out’ the negative and the resultant ‘average’ is zero.  The measure which best takes into account the magnitude of the sound pressure fluctuations, but not the direction, is the root-mean square (or RMS) sound pressure.

Question 8

Sound power (PWL)

Answer 8

Sound power is the total sound energy generated by the source per unit of time expressed in units of watts (W). The sound power of a source output is constant, regardless of its location although, as will be shown, the sound intensity and sound pressure will change as a function of the environment in which it is located.

Question 9

Sound intensity

Answer 9

Sound intensity is sound power per unit area (W/m2). It is a vector quantity, i.e. is specified by direction. Note: Sound intensity is proportional to sound pressure squared.

Question 10

Sound pressure (SPL)

Answer 10

The sound pressure level (SPL) is the variation of pressure superimposed on the atmospheric pressure. Sound pressure is expressed as force per unit area, and the preferred unit is the Pascal (Pa) (or Newton per square meter N/m2). When measured in sound pressure the hearing scale runs from 20μPa (20 × 10−6Pa) at the threshold of hearing to 200 Pa (200 000 000 μPa) at the threshold of pain. Note: compared to static air pressure (101.325 kPa – often approximated to 105 Pa) these variations are very small. Sound pressure is the ‘effect’ of a disturbance (what is heard). The actual ‘cause’ of the disturbance, and the resulting reaction effect, is due to the sound power. The sound pressure equates to the sound power plus a constant (k) which is dependent upon the acoustics of the environment, the directivity of the sound and the distance from the source.

Question 11

Rules of the decibel scale 2

Answer 11

10dB expresses a 10 times increase in sound intensity but, to the subjective listener, seems about twice as loud, i.e. it would take ten violins to sound twice as loud as one violin. 3dB expresses a doubling in sound intensity (i.e. If one machine gave a sound pressure level of 75 dB two identical machines would give a reading of 78 dB) although this would give rise to a just noticeable change.

Question 12

LEPd

Answer 12

daily personal noise exposure

Question 13

Leq

Answer 13

To determine the average dose received over a given time, an integrated sound level meter balances out the peaks and troughs to calculate a single figure that would give the equivalent dose over that time. This equivalent level is known as an Leq

Question 14

Noise exposure levels equivalent to 80dB(A)LEPd (the lower exposure action value – see Table 6.5), can be calculated using the ‘rule of three’.

Answer 14

80dB(A) over 8 hours is the same noise dose as 83dB(A) over 4 hours. Double the noise level (increase by 3dB) over half the time gives the same dose.

Question 15

For sound to travel through the ear, four different types of energy are required:

Answer 15

 Acoustical energy or sound waves set the tympanic membrane into vibration synchronous to the sound pressure compression and rarefaction cycles.  Mechanical energy as the vibration is transmitted by the movement of the eardrum and the ossicular chain.  A travelling wave, through the scala tympani as the oval window is pushed in, by the piston-like motion of the stapes footplate.  Biochemical energy that sends an electrical signal along the cochlear nerve to the auditory cortex for interpretation as sound.

Question 16

Health effects of noise Hearing loss may be

Answer 16

conductive, sensorineural, or mixed

Question 17

Conductive hearing loss

Answer 17

Conductive hearing loss occurs when the sound pathway is blocked in the outer and/or middle ear, reducing the vibration that reaches the inner ear. Conductive hearing loss is diagnosed when bone conduction hearing thresholds are better than air conduction thresholds.

Question 18

Sensorineural hearing loss

Answer 18

Sensory hearing loss is specific to the cochlea and neural hearing loss is due to pathology within the auditory nerve and/or central auditory pathway. The term sensorineural hearing loss is used to cover both a specific diagnosis is difficult without sophisticated diagnostic equipment. Sensorineural hearing loss is less likely to be medically treatable and more likely to be permanent than conductive hearing loss. Sensorineural hearing loss can be caused by medications or environmental exposure to certain chemicals. More relevant examples of sensorineural hearing loss are:  Prebyacusis – or age-related hearing loss (ARHL)  Noise-induced hearing loss (NIHL).

Question 19

A temporary threshold shift (TTS) is

Answer 19

a hearing loss which shows some recovery within 24-48 hours after the noise exposure stops. The more intense (louder/longer) the exposure, the longer the expected recovery period would be.

Question 20

permanent threshold shift (PTS)

Answer 20

Hearing loss which persists more than 30 days after the noise exposure is considered to be permanent threshold shift (PTS) and recovery is unlikely.

Question 21

Where the health surveillance identifies hearing damage the employer shall ensure that the employee is examined by a doctor. If the doctor considers that the damage is likely to be the result of exposure to noise, the employer shall:

Answer 21

a) ensure that a suitably qualified person informs the employee b) review the risk assessment c) review control measures d) consider assigning the employee to alternative work where there is no risk from further noise exposure e) ensure continued health surveillance and a health for any other employee who has been similarly exposed.

Question 22

Interpreting the audiogram

Answer 22

 Frequency (Hz) is plotted from low to high pitch along the x axis (horizontal).  Intensity (dB HL) is plotted from soft to loud along the y axis (vertical).  Air conducting thresholds are indicated by an ‘X’ for the left ear and an ‘O’ for the right ear.  Noise induced hearing loss typically presents with a classic ‘notch’ at around 4kHz.

Question 23

Test Probable noise level A risk assessment will be needed if the noise is like this for more than:

Answer 23

The noise is intrusive but normal conversation is possible 80dB 6 hours You have to shout to talk to someone 2 m away 85dB 2 hours You have to shout to talk to someone 1 m away 90dB 45 minutes

Question 24

Workplace noise survey – methodology Factors to consider

Answer 24

Location of measurement Duration of measurement Sample measurements for a group Mobile workers and highly variable daily exposures Measurements close to the ear Sources of error and other factors influencing the measurement result

Question 25

Location of measurement

Answer 25

When measuring to estimate a person’s noise exposure, measurements should be taken at every location the person works in or passes through during the working day, and the time spent at each location should be noted. Exposures to sound pressure levels (SPL) below 75 dB are not typically recorded as they are insignificant in relation to the daily noise exposure action levels. Measurements should be made at the position occupied by the person’s head, preferably with the person not present. If the operator needs to be present while the measurements are made (to control a machine or process, for example) the measurements should be made with the microphone positioned approximately 15cm away from the operator’s head on the side where noise levels are higher. This is close enough to obtain a reliable measure of the noise exposure, but not so close that reflections cause errors. To avoid making large numbers of measurements where, for example, the SPL is changing or if the person is moving within a noisy area, the worst case should be taken and measurements made at the noisiest location, or during the loudest periods. Alternatively, carrying out a spatial-average measurement by following the movement of the worker may provide a representative measure of the noise exposure. When using a dosemeter the microphone should be positioned on the shoulder (ideally on the shoulder joint) and measures taken to prevent it touching the neck, rubbing on or being covered by clothing or protective equipment. The dosemeter body should be placed securely in a pocket or on a belt where it can be safe from damage during the measurement.

Question 26

Duration of measurement

Answer 26

The noise level to which an individual employee is exposed will normally change throughout the day as different jobs are done and different machines or materials are used at different times. Enough noise measurements should be taken to account for all these changes, and the sound level and the person’s exposure duration at each noise level should be recorded. With a sound level meter measurements should be:  made at each position or during each job or task  made over a long enough period to obtain a representative measurement of the level the person is exposed to. The LAeq for the entire period may need to be measured but often a shorter measurement can be sufficient. In general:  If the noise is steady, a short sample LAeq measurement may be enough.  If the noise is changing, wait for the LAeq reading to settle to within 1 dB.  If the noise is from a cyclic operation measure the LAeq over a whole number of cycles. The measurement should cover all significant noise during the job or task, especially any short-duration, high-level noise exposures which may have a significant impact on the true LAeq. Noise dosemeters are designed to operate for long periods. They are ideal for measurements over an entire shift, or for a period of several hours during a shift. If measurements are made over part of a shift the period of your measurement should cover all significant noise exposure, so as to be typical of the working day and to enable a reliable prediction of the full daily exposure. Very short measurements should be avoided as they can be inaccurate due to the limited resolution of the dosemeter’s display. Steps should be taken to try and ensure that the dose reading relates to actual true noise exposure, not false input from unrepresentative noise sources when the meter is not supervised, for example: artificial bangs to get a ‘better score’, or tampering with the microphone.

Question 27

Sample measurements for a group

Answer 27

If several workers work in the same area, the exposure for them all may be estimated from measurements in selected locations and for appropriate durations to determine the highest exposure that someone is likely to receive.

Question 28

Mobile workers and highly variable daily exposures

Answer 28

For some jobs (such as maintenance) the work and the noise exposure will vary from day to day so there is no typical daily exposure. For people in these jobs, measurements need to be made of the range of activities undertaken, possibly over several days. From these measurements the likely daily exposure for a nominal day or days should be estimated.

Question 29

Measurements close to the ear

Answer 29

Measurements close to the ear, such as sound from a communication headset, or under a motorcycle helmet, require specialist equipment and procedures.

Question 30

Sources of error and other factors influencing the measurement result

Answer 30

The relevant variables should be revealed during an analysis of the work under consideration and during measurements. If significant contribution from sources of error is detected, the measurements should be rejected or corrected. The measured noise exposure and the uncertainty in the result depend on the measurement method used. A dosemeter tends to increase the potential false contributions to measurements and thereby the measured sound pressure level. However, using a hand-held sound-level meter may lead to an underestimation of the worker’s noise exposure. This is particularly connected to the difficulty in assessing the contribution from close-to-ear sound levels and noise from hand-held tools.

Question 31

Lower exposure action value

Answer 31

80 dB(A) 135 dB(C) Provide information and training.  Make hearing protection available.

Question 32

Upper exposure action value

Answer 32

85 dB(A) 137 dB(C)  Take reasonably practicable measures to reduce noise exposure (engineering controls / technical measures).  Provide mandatory hearing protection pending engineering controls and, where necessary, after engineering controls.

Question 33

Exposure limit value

Answer 33

87 dB(A) 140 dB(C)  Ensure level is not exceeded, taking hearing protection into account.

Question 34

Noise transmission pathways

Answer 34

Noise energy can be transmitted directly through the air or can be transmitted through other materials such as structural components. Noise energy also reflects off solid surfaces.

Question 35

Noise control strategies involve controls at the

Answer 35

source, the pathway and at the receiver

Question 36

The ability of a material to absorb, reflect and transmit sound can be measured. Two particular indices are useful when specifying structural materials:

Answer 36

 The sound absorption coefficient indicates how well a material absorbs the sound energy it receives. The higher the figure the more sound is absorbed. The coefficient can be determined for sounds at different frequencies. It is calculated as: intensity of sound absorbed by material intensity of sound incident on the same area of material Sound absorption coefficients for common building materials can be found in Approved Document E to the Building Regulations.  The sound reduction index (SRI) or ‘transmission loss’ is a measure of the attenuation provided by a material. It is the difference in dB between the noise energy falling onto a material and the level transmitted through it. Real world measures are unlikely to match the stated index which is determined by laboratory tests and does not address secondary transmission pathways.

Question 37

Noise control hierarchy

Answer 37

 Eliminate the risks by doing the work in a different way or by eliminating or minimising exposure to noise.  Modify the work, process or machine to reduce noise emissions.  Replace the tools and equipment used with lower noise alternatives.  Arrange the workplace and workflow to separate people from the noise.  Controlling the noise on its path from the source to reduce the noise reaching people.

Question 38

Consider the source of noise:

Answer 38

 Replace the machine with one with lower noise emissions (if cost effective).  Move the machine to an area with fewer employees (so long as it does not disrupt production).  Properly maintain the machine.  Modify parts of the machine, for example: by replacing components with quieter ones.

Question 39

Consider how the noise source radiates noise:

Answer 39

 Isolate or dampen any vibrating panels.  Isolate the machine from the building with isolation mounts or foundations.  Reduce the noise caused by impacts from falling material by adding damping material to receiving trays and chutes and/or reducing the distance the material falls.  Line machinery guards with sound-absorbing material (taking care not to compromise ventilation).  Fit silencers to air and gas inlets and exhausts.  Fit silencers to compressed air systems, or direct the exhaust away from the working area.

Question 40

Consider the path of the noise:

Answer 40

 Position the worker away from the source of noise.  Fit a suitably designed enclosure around a machine (if it does not require ‘hands on’ operation).  Position employees in a noise haven if enclosing the whole machine would be difficult.  Erect acoustic barriers or screens to separate quiet operations from noisy ones.  Add absorptive materials to the building to reduce reverberant noise (echoes).  Use active noise control to counter constant low-frequency tones from fans and dryers.

Question 41

Technical controls

Answer 41

Screens and barriers - placing an obstacle between the noise source and the people Damping - adding material to reduce vibration and noise Isolation - separate the machine from its surroundings and supporting structures Active noise control - electronically-controlled noise-reduction

Question 42

The receiver can be protected from the effects of noise by:

Answer 42

 positioning (distance)  reduction of the time exposed  provision of PPE.

Question 43

The following factors should be considered in selecting appropriate hearing protection: 9

Answer 43

 types of protector, and suitability for the work being carried out  noise reduction (attenuation) offered by the protector  compatibility with other safety equipment  pattern of the noise exposure  the need to communicate and hear warning sounds  environmental factors such as heat, humidity, dust and dirt  cost of maintenance or replacement  comfort and user preference  medical condition of the wearer.

Question 44

The risk assessment should consider:

Answer 44

(a) the level, type and duration of exposure, including any exposure to peak sound pressure (b) the effects of exposure to noise on employees or groups of employees whose health is at particular risk from such exposure (c) so far as is practicable, any effects on the health and safety of employees resulting from the interaction between noise and the use of ototoxic substances at work, or between noise and vibration (d) any indirect effects on the health and safety of employees resulting from the interaction between noise and audible warning signals or other sounds that need to be audible in order to reduce risk at work (e) any information provided by the manufacturers of work equipment (f) the availability of alternative equipment designed to reduce the emission of noise (g) any extension of exposure to noise at the workplace beyond normal working hours, including exposure in rest facilities supervised by the employer (h) appropriate information obtained following health surveillance, including, where possible, published information (i) the availability of personal hearing protectors with adequate attenuation characteristics.

Question 45

The international standard for human vibration measurement

Answer 45

Acceleration is measured in metres per second per second (m/s2).

Question 46

The international standard for human vibration measurement

Answer 46

Acceleration is measured in metres per second per second (m/s2).

Question 47

Whole-body vibration is

Answer 47

shaking or jolting of the human body through a supporting surface (usually a seat or the floor), for example: when driving or riding on a vehicle along an unmade road, operating earthmoving machines or standing on a structure attached to a large, powerful, fixed machine which is impacting or vibrating.

Question 48

Hand arm vibration is

Answer 48

vibration transmitted from work processes into workers’ hands and arms. It can be caused by operating handheld power tools, such as road breakers, and hand guided equipment, such as powered lawnmowers, or by holding work pieces being machined.

Question 49

A tiered approach to health surveillance is sensible.

Answer 49

 The first level is to use questionnaires to identify workers who may be at risk or may be experiencing early symptoms.  The second level would involve an assessment by an occupational health nurse. If ill-health was indicated the third level would involve a referral to an occupational health physician for a formal diagnosis.  Medical assessments are more appropriate for hand arm vibration syndrome (HAVS) as the early signs of vibration white finger (VWF) can be tested for.

Question 50

The HSE has also developed a simple ‘exposure points’ system to estimate the daily exposure –

Answer 50

Multiply the points assigned to the tool vibration by the number of hours of daily ‘trigger time’ for the tool(s) and then compare the total with the exposure action value (EAV) and exposure limit value (ELV) points. EAV = 100 points per day ELV = 400 points per day

Question 51

Hand Arm Vibration (HAV) What are the risk factors?

Answer 51

 Frequency of the vibration - 2 to 1,500 Hz is potentially damaging - 5 to 20 Hz is most dangerous  Magnitude of the energy measured in m/s2  Strength of the grip and other forces necessary to hold or guide the tool or work-piece  Duration of exposure  Frequency of exposure  Low temperature  Individual factors, for example: smoking, susceptibility to vibration energy, age, health and general well-being

Question 52

Hand Arm Vibration (HAV) Exposure Action Value (EAV)

Answer 52

 Above which employers are required to take action to control exposure  2.5 m/s2 A(8)

Question 53

Hand Arm Vibration (HAV) Exposure Limit Value (ELV)

Answer 53

 Maximum amount of vibration an employee may be exposed to on any single day  5 m/s2 A(8)

Question 54

Hand Arm Vibration (HAV) How is it controlled?

Answer 54

 Eliminate the need for a worker to hold vibrating equipment, for example: automate a process  Minimise the required force or grip on the tool or work piece  Provide suitable low vibration tools  Ensure the right tool is used for each job  Ensure tools have been properly maintained to avoid increased vibration caused by faults or general wear, and keep cutting tools sharp so that they remain efficient  Reduce the amount of time vibrating tools are used (work scheduling / job rotation / rest breaks)  Use of dose monitors / limiters  Keep workers warm and dry (provide gloves, a hat, waterproofs and heating pads if required)  Provide workers with information and training on the risks and precautions

Question 55

Whole Body Vibration (WBV) What are the risk factors?

Answer 55

Unusually high vibration or jolting or the vibration is uncomfortable for a long time on most working days

Question 56

Whole Body Vibration (WBV) Exposure Action Value (EAV)

Answer 56

 Above which employers are required to take action to control exposure  0.5 m/s2 A(8)

Question 57

Whole Body Vibration (WBV)Exposure Limit Value (ELV)

Answer 57

 Maximum amount of vibration an employee may be exposed to on any single day  1.15 m/s2 A(8)

Question 58

Whole Body Vibration (WBV) How is it controlled?

Answer 58

 Select vehicles and machines with the appropriate size, power and capacity for the work and the ground conditions.  Maintain vehicle suspension systems correctly (for example: cab, tyre pressures, seat suspension).  Make sure that paved surfaces or site roadways are well maintained, for example: potholes filled in, ridges levelled, rubble removed.  Train and instruct operators and drivers to be able to adjust seat positioning and driver weight setting on suspension seats.

Question 59

The risk assessment should consider:

Answer 59

(a) the magnitude, type and duration of exposure, including any exposure to intermittent vibration or repeated shocks (b) the effects of exposure to vibration on employees whose health is at particular risk from such exposure (c) any effects of vibration on the workplace and work equipment (d) manufacturers information (e) the availability of lower vibration replacement equipment (f) any extension of exposure beyond normal working hours including at rest facilities (g) specific working conditions such as low temperatures (h) appropriate information obtained from health surveillance