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Noise Testing
Excessive Noise Endangers the Health of your Employees and Could Cost You Money! Tecforce has the Solution! Your hearing is precious. When it is damaged it cannot be repaired. Tecforce can help you to minimise your employees' exposure to excessive noise by monitoring your exposure levels, preventing hearing damage. HOW DO WE HEAR? The ear is composed of three sections: the outer, middle and inner ear (see Figure 1).
The middle ear consists of three tiny bones, (ossicles), that connect the eardrum to the inner ear, and deliver sound from the ear canal to the inner ear.
The inner ear (cochlea), is susceptible to damage from continued exposure to high-level noise. The vibrating motion of the ossicle produces a wave motion in a membrane. On top of this are thousands of small hairs with nerves connected to each hair cell. When a hair cell is bent because of membrane motion, the nerve fires and the message is transmitted to the brain.
If the hair cells in a particular region of the cochlea are destroyed, the nerves will not fire and the brain will not receive any information. If part of the hair cells are destroyed, the brain may receive a distorted message that it cannot interpret. When the microscopic structures are damaged, there is no way to repair them to restore reasonable hearing. Typically, hair cells are damaged or destroyed when their supporting structures are overworked. With continued exposure to high-level noise, the membrane motion is great and the cells that support the hair cells swell. Eventually, they rupture and the hair is destroyed or damaged. Only a few hair cells may be lost at a time, but with repeated exposure the cumulative effect can be substantial. PROPERTIES OF SOUND We cannot see sound, but it is still a force with real dimensions and three definite properties:
Intensity is the loudness of a sound, or the pressure it exerts through the ear, measured in decibels (dB). Typically, a person begins to identify sounds when a level of 10 to 15 dBs is reached; this is the threshold of hearing. The other end of the scale is known as the threshold of pain (140 dB), or the point at which the average person experiences pain. (See Table 1).
In assessing noise, a special measure called "dBA" indicates damage to hearing. This is provided for many pieces of workshop equipment. The higher the dBA number, the greater the risk of damage to hearing.
Frequency is the number of sound waves (high and low pressure areas) produced by a noise source passing a given point per second. This is measured in cycles per second, or hertz (Hz). The most dangerous sounds are high in intensity (dB level) and have a high frequency. This is because a large number of sound waves are transmitted to the ears with a force greater than your ears can tolerate.
Duration is the amount of time you are exposed to a sound level. In the above table the right-hand column lists various high sound levels and the left-hand column indicates the length of exposure that is safe for the corresponding noise level during a day.
For example, the average person can be exposed to a sound source producing 90 dBA for a maximum of eight hours. If the sound level is at 100 dBA, then the maximum exposure is two hours. NOISE AND THE LAW The Noise at Work Regulations 1989 SI:179 (a statutory instrument empowered under section 15 of the Health & Safety at Work Act 1974 to meet the requirement of EC directive 86/188/EEC) are intended to reduce damage to hearing caused by noise, and lay down criteria when workers? daily exposure (averaged over an 8 hour working period) reaches three ?action levels?: First Action Level = 85 dB(A)
The employer must assess the risks and take action. Measurements must be taken by ?competent personnel?. Employees are entitled to wear hearing protection on request, and the employer must provide information and training on hearing protection.Second Action Level = 90 dB(A)
This maximum daily dose should not be exceeded. Further action must be taken (ie reduce the noise where practicable). You must create a marked ?ear protection zone? where hearing protectors must be worn if this level is still exceeded.Peak Action Level = 140 dB(A)
Hearing protectors must be worn, and ?ear protection zones? must be clearly marked.The Regulations require employers to take action to reduce their employees' exposure to harmful noise levels. This action can be to take action at source (i.e. the machine or tool), or by using suitable ear protection in the area where the hazard persists. The exposure levels take no account of the effect of any ear protector used. Tecforce can advise you and perform your noise testing in line with the new European Physical Agents Directives. HOW IS IT TESTED? Tecforce's experienced environmental team will use "clip-on" and hand-held Personal Dosimeters to conduct a noise survey which will measure the noise ?dose? for each of your activities, and calculate your workers? daily exposure level. We will then advise you of any actions that you need to carry out, and make realistic suggestions. We will also help you to compile records of the measurements taken, in order to ensure compliance with NAWR. We can also provide hearing training for your employees.
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