managing safely Noise at Work Course Notes Mark Mallen Group Health and Safety Manager December 2005 Noise at Work: Version 1 Page 1 of 23

Transcription

1 Noise at Work Course Notes Mark Mallen Group Health and Safety Manager December 2005 Noise at Work: Version 1 Page 1 of 23

2 Course Content 1. What is noise? 2. Sound - Sound Waves 3. How do we hear? - The Ear 4. The measurement of noise - Decibels 5. Hearing Loss - Noise Induced Hearing Loss - Chronic NIHL - Temporary Threshold Shift TTS - Permanent Threshold Shift PTS - Socioacusis 6. The Law - Noise at Work Regulations The Control of Noise at Work Regulations Employers Duties - Employees Duties 7. Information, instruction, and training - What we need to tell you - Exposure areas above the lower exposure action values - What we are doing to control risks and exposures - Where and how people can obtain hearing protection - How to report defects in hearing protection and noise-control equipment - Duties under the Noise Regulations What do I have to look out for? - What you should do to minimise the risk, - Earmuffs - Earplugs - Semi-inserts/caps Noise at Work: Version 1 Page 2 of 23

3 What is Noise? Noise Noise is unwanted sound. One person s music could be another s noise! The ear does not differentiate between noise and sound - The brain does that! Effects Short term Annoy Distract Long term Deafness Tinnitus Noise Induced Hearing Loss Noise at Work: Version 1 Page 3 of 23

4 Sound This is the sensation produced via the ear, which results from fluctuations in the pressure of the air around us. Vibrating air molecules produce these pressure fluctuations. The source of the sound causes the air molecules to vibrate. The transmission of these sound pressure waves is like ripples on a pond. The sound transmits in waves and has certain characteristics. Noise at Work: Version 1 Page 4 of 23

5 A Sound Wave A vibrating object creates a sound wave. The vibrating object, which creates the disturbance, could be: The vocal chords of a person A guitar string A machine Traffic The vibrating diaphragm of a radio speaker. Regardless of what vibrating object is creating the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth motion. This is known as the frequency of a wave. The frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. If a particle of air undergoes 1000 vibrations in 2 seconds, then the frequency of the wave would be 500 vibrations per second. The unit of frequency is the Hertz (abbreviated Hz), where: 1 Hertz = 1 vibration/second The frequency, at which each particle vibrates, as a sound wave moves through a medium, is the same as the frequency of the original source of the sound wave. Subsequently, a guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz, which carries a sound signal to the ear of a listener, which is detected as a 500 Hz sound wave. The human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to Hz. Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound and any sound with a frequency above the audible range of hearing (i.e., more than Hz) is known as an ultrasound. Noise at Work: Version 1 Page 5 of 23

6 How do we hear Sound? The Ear The ear consists of three basic parts: The outer ear The middle ear The inner ear Each part serves a specific purpose in the task of detecting and interpreting sound. The outer ear collects and channels sound to the middle ear. The middle ear transforms the energy of a sound wave into internal vibrations via a bone structure. The inner ear transforms these vibrations into nerve impulses, which transmit to the brain. The Outer Ear Noise at Work: Version 1 Page 6 of 23

7 The outer ear consists of an earflap and an ear canal, which is approximately 2-cm long. The earflap provides protection for the middle ear, in particular the eardrum. It also channels sound waves, via the ear canal, to the eardrum. As sound travels through the outer ear, it is still in the form of a sound pressure wave. It is not until the sound reaches the eardrum, at the interface of the outer and the middle ear that the energy of the mechanical wave converts into vibrations, by the inner bone structure of the ear. The Middle Ear The middle ear is an air-filled cavity, which consists of an eardrum and three tiny, interconnected bones - the hammer, anvil, and stirrup. The eardrum is a very durable, tightly stretched membrane, which vibrates as the incoming sound pressure waves reach it. As the eardrum connects to the hammer, the movements of the eardrum will set the hammer, anvil, and stirrup bones into motion at the same frequency of the sound wave. The three tiny bones of the middle ear act as levers to amplify the vibrations of the sound wave. Since the pressure wave striking the large area of the eardrum is concentrated into the smaller area of the stirrup, the force of the vibrating stirrup is nearly 15 times larger than that of the eardrum. This feature enhances our ability of hear the faintest of sounds. In addition, the Eustachian connects the middle ear via a tube to the mouth. This connection allows for the equalization of pressure within the air-filled cavities of the ear. When this tube clogs i.e. during a cold, the ear cavity is unable to equalise pressure; this will often lead to earaches and other pains. The stirrup connects to the inner ear, and the vibrations of the stirrup transmit to the inner ear, via the oval window. The inner ear is full of fluid and the mechanical movement of the stirrup creates a wave within this fluid. The Inner Ear The inner ear consists of a cochlea, the semicircular canals, and the auditory nerve. The cochlea and the semicircular canals contain a water-like fluid. The fluid and nerve cells of the semicircular canals provide no roll in the task of hearing; they merely serve as accelerometers for detecting accelerated movements and assisting in the task of maintaining balance. Noise at Work: Version 1 Page 7 of 23

8 The cochlea is a snail-shaped organ, which would stretch to approximately 3 cm. It is filled with fluid and the inner surface is lined with over hair-like nerve cells, which perform one of the most critical roles in our ability to hear. These nerve cells differ in length by minuscule amounts; they also have different degrees of resiliency to the fluid, which passes over them. As a wave moves from the interface between the hammer of the middle ear and the oval window of the inner ear through the cochlea, the small hair-like nerve cells are set in motion. Each hair cell has a natural sensitivity to a particular frequency of vibration. When the frequency of the wave matches the natural frequency of the nerve cell, an electrical impulse is released, which passes along the auditory nerve towards the brain. The brain then interprets the qualities of the sound upon reception of these electric nerve impulses. Noise at Work: Version 1 Page 8 of 23

9 The Measurement of Noise Decibels Humans are equipped with very sensitive ears, capable of detecting sound waves of extremely low intensity. The faintest sound that the typical human ear can detect has an intensity of 1*10-12 W/m 2. This corresponds to a sound, which will displace particles of air by a mere one-billionth of a centimetre. This sound is known as the Threshold of Hearing. The most intense sound, which the ear can safely detect without suffering any physical damage, is more than one billion times more intense than the threshold of hearing and is known as the Threshold of Pain. Since the range of intensities, which the human ear can detect, is so large, a scale based on multiples of 10 is used. This type of scale is known as a logarithmic scale. The scale for measuring intensity is the decibel scale. Decibels are written as db The threshold of hearing is assigned a sound level of 0 decibels, abbreviated 0 db. A sound, which is 10 times more intense, is assigned a sound level of 10 db. A sound, which is 10 x 10 or 100 times more intense, assigned a sound level of 20 db. A sound, which is 10 x 10 x 10 or 1000 times more intense, is assigned a sound level of 30 db. A sound, which is 10 x 10 x 10 x 10 or times more intense, is assigned a sound level of 40 db. This scale is based on powers or multiples of 10. Noise at Work: Version 1 Page 9 of 23

10 The table below lists some common sounds with an estimate of their decibel level. Source Threshold of Hearing - TOH Rustling Leaves Whisper Normal Conversation Busy Street Traffic Vacuum Cleaner Large Orchestra Walkman at Maximum Level Front Rows of Rock Concert Threshold of Pain - TOP Military Jet Takeoff Instant Perforation of Eardrum Intensity Level 0 db 10 db 20 db 60 db 70 db 80 db 98 db 100 db 110 db 130 db 140 db 160 db It is important to remember that a doubling in sound represents an increase of only 3dB. Noise at Work: Version 1 Page 10 of 23

11 Hearing Loss The ear is a fantastic instrument, capable of dealing with a huge range of sounds and helps to make them intelligible. However, it can be easily damaged, by: Medical conditions Accidents Drugs Congenital conditions Social activities Prolonged exposure to high noise levels Workers at risk of hearing damage are usually those in heavy productive industry, such as: Metal work Construction Quarrying Steel work Mining Exposure to noise levels above 90 db (A) is likely to cause damage to a significant proportion of the population with continued exposure. This is known as Noise Induced Hearing Loss. Noise at Work: Version 1 Page 11 of 23

12 Noise Induced Hearing Loss The cause of NIHL is not completely known. However, we do know that the damage is caused to the sensitive cells in the cochlea. For reasons, which are not entirely clear, some of the cells in the sensory organ (Organ of Corti) are more sensitive than others. Chronic NIHL This disease process occurs gradually over many years of exposure to less intense noise levels and is associated with chronic exposure to high intensity, continuous noise. The amount of sound that is capable of producing cochlear damage and subsequent hearing loss is based upon the equal energy concept. Therefore, it is the total sound energy delivered to the cochlea that is relevant in predicting injury and hearing loss. Both an intense sound presented to the ear for a short period and a less intense sound that is presented for a longer period will produce equal damage to the inner ear. An increase in sound intensity of 3dB represents a doubling of sound pressure. Therefore, for each 3dB increase in sound exposure, exposure must be cut in half in order to deliver equal sound energy to the ear. The development of chronic NIHL progresses through two phases, permanent and temporary threshold shift. Temporary Threshold Shift TTS The first stage is characterised by a temporary threshold shift - TTS. This brief hearing loss, characterised by ringing in the ears, occurs after noise exposure, and completely resolves after a period of rest. This can be thought of as auditory fatigue and most studies indicate that no sensory cell damage occurs. After repeated exposure to noises intense enough to produce TTS, eventually a Permanent Threshold Shift - PTS will occur. Permanent Threshold Shift PTS This is the second stage of chronic NIHL and is an irreversible increase in hearing thresholds. At this point, there has been irreversible hair cell damage. Once you have it, it is too late! Sufferers report difficulty understanding speech rather than hearing speech. This difficulty is particularly noticeable in environments with significant background noise. Noise at Work: Version 1 Page 12 of 23

13 An normal audiogram An audiogram showing the classic dip in hearing performance PTS is characterised by a loss of consonant discrimination. Consonant sounds such as f, s, t, d, sh, and k are all high frequency sounds (3-kHz) and although they are not responsible for the power of speech, they are essential to the intelligibility of speech. Noise at Work: Version 1 Page 13 of 23

14 An audiogram showing loss of speech sounds Socioacusis In today s noisy society, even people with quiet jobs may suffer from NIHL. Such non-occupational NIHL is also called socioacusis. Sources of non-occupational noise include: Gunfire Loud music Open vehicles Power tools Noise at Work: Version 1 Page 14 of 23

15 The Law Exposure to high noise levels can cause incurable hearing damage. Usually the important factors are: The noise level. How long people are exposed to the noise, daily and over a number of years. Sometimes the peak pressure of the sound wave may be so great that there is a risk of instantaneous damage. To protect everyone from the harmful effects of noise, the Government, through the HSE introduced the following legislation: Noise at Work Regulations 1989 The Regulations place responsibilities on employers, employees, and people who make and supply noisy machinery. At the workplace, primary responsibility lies with the employer. Nevertheless, both management and workers need to be involved if action is to be effective. To protect hearing, the regulations introduced three thresholds: First Action Level - 85dB(A) Second Action Level - 90dB(A) Peak Action Level Pascals or 140dB The action levels are values of daily personal exposure: L EP, d The sound at the ear is represented by (A) Noise at Work: Version 1 Page 15 of 23

16 First Action Level - L EP, d 85dB(A) The approximate level at which you have to raise your voice to be heard at 2 metres. The employee must be trained and hearing protection must be made available upon request. Second Action Level - L EP, d 90dB(A) The approximate level at which you have to raise your voice to be heard at 1 metre. A noise reduction programme must be implemented. Areas must be marked and employees must be provided with hearing protection, which must be worn. Peak Action Level Pascals or 140dB This relates to sudden noise and the duties are similar to those required by the second action level. The main requirements apply where noise exposure is likely to be at or above any of three 'Action Levels', as summarised in the table overleaf: The Control of Noise at Work Regulations 2005 come into force on 6th April 2006 Exposure limit values and action values 4. (1) The lower exposure action values are (a) a daily or weekly personal noise exposure of 80 db (A-weighted); and (b) a peak sound pressure of 135 db (C-weighted). (2) The upper exposure action values are (a) a daily or weekly personal noise exposure of 85 db (A-weighted); and (b) a peak sound pressure of 137 db (C-weighted). (3) The exposure limit values are (a) a daily or weekly personal noise exposure of 87 db (A-weighted); and (b) a peak sound pressure of 140 db (C-weighted). Noise at Work: Version 1 Page 16 of 23

17 Action required where L EP, d is likely to be: (see note 1 below) Below 85 db(a) 85dB(A) First AL 90 db(a) Second AL Employer s Duties Regulation 6 - General duty to reduce risk Risk of hearing damage to be reduced to the lowest X X X (2) level reasonably practicable Regulation 4 - Assessment of noise exposure To be made by a competent person - X X Regulation 5 - Record of Assessments To be kept until a new one is made - X X Regulation 7 - Noise Reduction Reduce exposure to noise, as far as is reasonably - X X practicable, by means other than ear protectors Regulation 11 - Provision of Information to Workers Provide adequate information, instruction and training about risks to hearing: What employees should do to minimise risk, - X X How they can obtain ear protectors if they are exposed to between 85 and 90 db(a) Their obligations under the Regulations Regulation 9 - Mark Ear Protection Zones With notices, so far as reasonably practicable - - X Ear protectors Regulation 8(1) - Provided to employees who ask - X - Regulation 8(2) - Provided to all exposed - - X Regulation 10(1)(b) - Maintained and repaired - X X Regulation 10(1)(a) - Used by all exposed - - X Regulation 9(1)(b) Ensure that all who go into a marked ear protection zone use ear protectors - - X (3) Maintenance and use of equipment Regulation 10(1)(a) Ensure that all equipment is used, except for ear protectors provided between 85 - X X and 90 db (A) Regulation 10(1)(b) - Ensure all equipment is maintained - X X Employees' Duties Regulation 10(2) - Use of Equipment Use ear protectors - - X Use any other protective equipment - X X Report any defects discovered to employer - X X Machine Makers' and Suppliers' Duties Regulation 12 - Provision of Information Provide information on the noise likely to be - X X generated Noise at Work: Version 1 Page 17 of 23

18 Notes: 1. The db(a) action levels are values of daily personal exposure (L EP, d ). 2. All the actions indicated at 90 db(a) are also required where the peak sound pressure is at or above 200 Pa (140 db re 20 MPa). 3. This requirement applies to all who enter the zones, even if they do not stay long enough to receive an exposure of 90 db(a) L EP,d Employers Duties Get the noise levels assessed by competent people. Keep a record of the assessments, until a new one is made. Where an assessment shows exposure is at, or above, any of the action levels: a) Inform personnel that there is a noise hazard b) Inform them of what to do, to keep risks to a minimum. Where the exposure needs to be controlled, quieten the workplace, if this can be done. Between the first and second action levels ensure that: a) Ear protection is freely available (ear muffs or plugs). b) Inform workers of the risk to their hearing, unless they wear protection. Where use of protection is compulsory, ear protection zones should be marked, if this is reasonably practicable. Make sure that everyone who goes into a marked zone, even for a short time, uses ear protection. Check to make sure the control measures are working. Make sure the equipment you provide is kept in good condition. If people work in noise at, or above, the second or the peak action level, the Regulations still require the reduction of noise exposure by means other than ear protectors, as far as this is reasonably practicable. Noise at Work: Version 1 Page 18 of 23

19 Employees Duties Wear the ear protection (earplugs or earmuffs) provided, whenever in places where the second or peak action levels might be reached and every entry into an area marked as an ear protection zone. Use any other equipment the employer provides under the Regulations. For example, if the machine is meant to have a silencer fitted- don't take it off. Look after any equipment provided under the Regulations. Report any equipment defects. Your employer should warn you when your exposure might reach the first action level and provide you with personal ear protectors if you want them. It is in your own interests to ask for them and to use them. Noise at Work: Version 1 Page 19 of 23

20 Information, instruction, and training What we need to tell you Exposure areas above the lower exposure action values What we are doing to control risks and exposures; Where and how people can obtain hearing protection; How to report defects in hearing protection and noise-control equipment; Duties under the Noise Regulations 2005; What you should do to minimise the risk, such as the proper way to use hearing protection and other noise-control equipment, how to look after it and store it, and where to use it; Noise at Work: Version 1 Page 20 of 23

21 Exposure areas above the lower exposure action values What we are doing to control risks and exposures Established advisory hearing protection zones Sourcing noise reduction blades Provide Hearing Protection Noise at Work: Version 1 Page 21 of 23

22 Where and how people can obtain hearing protection Freely available from dispensers or production manager How to report defects in hearing protection and noise-control equipment Report to Supervisor or Manager Duties under the Noise Regulations 2005 Wear the ear protection (earplugs or earmuffs) provided, whenever in places where the second or peak action levels might be reached and every entry into an area marked as an ear protection zone. Use any other equipment the employer provides under the Regulations. For example, if the machine is meant to have a silencer fitted- don't take it off. Look after any equipment provided under the Regulations. Report any equipment defects. What do I have to look out for? Hearing protection such as earmuffs and earplugs is your last line of defence against damage, so check the following: What you should do to minimise the risk such as the proper way to use hearing protection and other noise-control equipment, how to look after it and store it, and where to use it; Earmuffs Make sure they totally cover your ears, Fit tightly and there are no gaps around the seals. Don t let hair, jewellery, glasses, hats etc interfere with the seal. Try and keep the seals and the insides clean. Don t stretch the headband too much make sure it keeps its tension. Earplugs They can be difficult to fit properly practice fitting them and get help if you are having trouble. Often they can look like they are fitted properly, but they may not be giving you much protection. Noise at Work: Version 1 Page 22 of 23

23 Clean your hands before you fit earplugs, and don t share them. Some types you use only once, others can be re-used and even washed make sure you know which type you have. Semi-inserts/caps Follow the same advice as for earplugs and make sure any headband keeps its tension. Remember hearing protection is provided to protect you, if you do not use it, you may lose it! Remember if in doubt, ask? Noise at Work: Version 1 Page 23 of 23