1. What kinds of health effects can be caused by exposure to noise? The two kinds of health effects of noise are non-auditory effects auditory effects Non-auditory effects include stress, related physiological and behavioural effects, and safety concerns. Auditory effects include hearing impairment resulting from excessive noise exposure. Noise- induced permanent hearing loss is the main concern related to occupational noise exposure.

2. The main auditory effects include: Acoustic trauma: Sudden hearing damage caused by short burst of extremely loud noise such as a gun shot. Tinnitus: Ringing or buzzing in the ear Temporary hearing loss: Also known as temporary threshold shift (TTS) which occurs immediately after exposure to a high level of noise. There is gradual recovery when the affected person spends time in a quiet place. Complete recovery may take several hours.

3. Permanent hearing loss: Permanent hearing loss, also known as permanent threshold shift (PTS), progresses constantly as noise exposure continues month after month and year after year. The hearing impairment is noticeable only when it is substantial enough to interfere with routine activities. At this stage, a permanent and irreversible hearing damage has occurred. Noise-induced hearing damage cannot be cured by medical treatment and worsens as noise exposure continues. When noise exposure stops, the person does not regain the lost hearing sensitivity. As the employee ages, hearing may worsen as "age-related hearing loss" adds to the existing noise- induced hearing loss.

4. The main characteristics of noise- induced hearing loss are: Noise-induced hearing loss is a cumulative process: both level of noise and exposure time over a worker's work history are important factors. At a given level, low-frequency noise (below 100 Hz) is less damaging compared to noise in the mid-frequencies (1000 - 3000 Hz). Noise-induced hearing loss occurs randomly in exposed persons. Some individuals are more susceptible to noise-induced hearing loss than others. In the initial stages, noise-induced hearing loss is most pronounced at 4000 Hz but it spreads over other frequencies as noise level and/or exposure time increases.

5. Aging Affects Hearing Loss Hearing sensitivity declines as people become older. This medical condition is called presbycusis. Again, just like noise- induced hearing loss, everyone is not affected equally. Age-related hearing loss adds to noise-induced hearing loss. Hearing ability may continue to worsen even after a person stops work in a noisy environment

6. Other causes of hearing loss Noise affects the hearing organs (cochlea) in the inner ear. That is why noise-induced hearing loss is sensory-neural type of hearing loss. Certain medications and diseases may also cause damage to the inner ear resulting in hearing loss as well. Generally, it is not possible to distinguish sensory- neural hearing loss caused by exposure to noise from sensory-neural hearing loss due to other causes. Workers in noisy environments who are also exposed to vibration (e.g., from a jack hammer) experience greater hearing loss than those exposed to the same level of noise but not to vibration.

7. Some chemicals are toxic; that is, they are toxic to the organs of hearing and balance or the nerves that go to these organs. This means that noise-exposed workers who are also exposed to toxic chemicals (e.g., toluene, carbon disulfide) may suffer from more hearing impairment than those who have the same amount of noise exposure without any exposure to toxic chemicals.

8. Hearing loss measured Hearing loss is measured as threshold shift in dB units using an audiometer. The 0 dB threshold shift reading of the audiometer represents the average hearing threshold level of an average young adult with disease-free ears. The PTS (permanent threshold shift), as measured by audiometry, is dB level of sounds of different frequencies that are just barely audible to that individual. A positive threshold shift represents hearing loss and a negative threshold shift means better than average hearing when compared with the standard.

9. How is the amount of hearing disability measured or expressed? Several methods of calculating the percentage of hearing disability are in use. The current method recommended by AMA(American Medical Association) is as follows: 1.The average hearing threshold level at 500, 1000, 2000, and 3000 Hz should be calculated for each ear.

10. 2. Multiplying should calculate the percentage of impairment for each ear (the monaural loss) by 1.5 times the amount by which the above average exceeds 25 dB (low fence). Hearing impairment is 100% for 92 dB average hearing threshold level. 3. The hearing disability (binaural assessment) is calculated by multiplying the smaller percentage (better ear) by 5, adding it to the larger percentage (poorer ear), and dividing the total by 6.

11. EXAMPLE The data in the table below show how audiometric readings are converted into percent hearing impairment. Table 1 Hearing Disability Calculation Using the American Medical Association Formula Frequency, HzHearing Threshold Level, dB Left EarRight Ear 500 1000 2000 3000 30 45 60 85 15 25 45 55

12. Sum Average Low fence Exceeds low fence %Impairment 220 55 25 30 45 140 35 25 10 15 Disability[45 + (5x15)]/6 = 20%

15. Relationship between noise exposure and hearing loss From the scientific data accumulated to date, it is possible to determine the risk of hearing loss among a group of noise exposed persons. To do this we need the following data: A measure of daily noise exposure level Duration of noise exposure (months, years) Age of person

17. Above figure shows Percent of exposed population with hearing loss greater than 25 dB for various noise levels and years of exposure as given by the ISO 1999-1990 method. Hearing loss is defined as average threshold shift at 500, 1000, 2000 and 3000 Hz. Noise-induced hearing loss occurs randomly. All exposed persons are not affected equally. Some highly susceptible people lose their hearing ability faster than others. Given a noise-exposed person, it is not possible to determine whether or not his or her hearing loss is due to noise.

18. However, in a group of exposed persons, the percentage of population with hearing loss depends on the level of noise exposure and the duration of exposure. For higher noise exposure levels, and longer durations of exposures, a larger percentage of exposed persons acquire hearing loss. This observation forms the basis for calculating noise-induced hearing loss as outlined in the international standard ISO1999-1990 and American National Standard ANSI S3.44 - 1996

22. Non-auditory effects Hearing loss from long term exposure to noise has been recognized as a hazard for a long time. However, what the non-auditory effects of noise are is still not certain. In general, the suspected effects include cardiovascular function (hypertension, changes to blood pressure and/or heart rate), and changes in breathing, annoyance, sleep, physical health and mental health. In the workplace, non-auditory effects of noise include problems with oral communications. It has also been shown that absenteeism appears to be higher among workers in noisy industries. It has not been concluded whether this is from psychological aversion to noise or from physiological consequences of noise stress

23. TYPES OF NON-AUDITORY EFFECTS Non-auditory effects can be divided into two categories - physiological effects and performance effects. Physiological effects The physiological effects can be temporary or permanent. Examples of temporary physiological effects are: The startling response to loud noise, where muscles burst into activities, generally, with the intention to protect The muscle tension response, where muscles tend to contract in the presence of loud noise

24. T he respiratory reflexes, where the respiratory rhythm tends to change when noise is present. Changes in the heart beat pattern changes in the diameter of the blood vessels, particularly in the skin As for the permanent effects, there is no consensus on the issue: some researchers tend to favour the theory that there are permanent effects, while others are skeptical on the issue.

25. Noise affect performance Noise can interfere with verbal communications and can be distracting and annoying. Below are some examples of how these factors can affect work performance. Speech intelligibility Speech intelligibility is the ability to understand spoken words. The presence of noise interferes with the understanding of what other people say. This includes face-to-face talks, telephone conversations, and speech over a public address system.

26. In order to be intelligible the sound level of speech must be greater than the background noise at the ear of the listener. People with otherwise unnoticeable hearing loss find it difficult to understand spoken words in noisy surroundings. In noisy work situations, people are able to converse with difficulty at a distance of one meter for a short time in the presence of noise as high as 78 dB(A). For prolonged conversations, the background noise level must be lower than 78 dB(A).

27. Speech Communication Capability versus Level of Background Noise in dB(A) Communication Below 50 dB(A) 50-70 dB(A) 70-90 dB(A) 90-100 dB(A) 110- 130 dB(A) Face-to-face (unamplified speech) Normal voice at distances up to 6 m Raised voice level at distances up to 2 m Very loud or shouted voice level at distances up to 50 cm Maximum voice level at distances up to 25 cm Very difficult to impossibl e, even at a distance of 1 cm TelephoneGoodSatisfacto ry to slightly difficult Difficult to unsatisfact ory Use press-to- talk switch and an acoustical ly treated booth Use special equipm ent

28. Annoyance Noise is annoying. If exposed to noisy environments, people generally prefer to reduce the noise loudness, avoid it, or leave the noisy area if possible. The same noise could be annoying to some people but acceptable to others. There is no definite relationship between the degree of annoyance or unpleasantness of noise and the risk of adverse health effects. For example, very loud music may be pleasant to one group of people and annoying to another group. Both groups will be equally at risk of hearing loss. Besides loudness of sound, several other factors contribute to annoyance.

29. Primary acoustic factors Sound level Frequency Duration Secondary acoustic factors Spectral complexity Fluctuations in sound level Fluctuations in frequency Rise-time of the noise Localization of noise source Physiology Factors that affect Individual Annoyance to Noise

30. Nonacoustic factors Adaptation and past experience How the listener's activity affects annoyance Predictability of when a noise will occur Is the noise necessary? Individual differences and personality

31. Job interference Depending of the type of activity, noise can severely affect efficiency of a task performance. The following examples will illustrate this point: a conversation nearby will distract a person and affect his or her concentration, hence reducing the employee's his efficiency a noisy environment could create an additional hazard, since audible alarms might not be heard a noisy environment interferes with oral communication and thus, interferes with the activity