Institute of Acoustics
Questions which competent persons should be readily able to solve using appropriate Data Sheets.
PART ONE: (ALL QUESTIONS TO BE ANSWERED)
1. Calculate the daily personal noise exposure of an employee whose working day consists of three tasks, with durations and noise levels shown.
4 hrs 30 mins
2 hrs 30 mins
2. A worker on a production line is exposed to continuous background noise, plus the noise from two machines, A and B. The level at his workstation is 93 dB with both machines running, 92 dB with machine A turned off, and 88 dB with both machines turned off. Determine the level of noise which could be produced by each machine running on its own in the absence of background noise.
When making measurements with a hand-held sound level meter to estimate noise exposure, what is the preferred measurement position? Outline two difficulties which might be encountered in achieving a measurement at the preferred position.
3. A nightclub bar-worker’s daily personal noise exposure is 88dB. What would be the increase in his noise exposure if he was t work an additional 1½ hours on the glass collection duties where the typical LAeq is 97dB?
4. Explain why the “C” frequency-weighting is commonly used when measuring peak sound pressure in occupational exposure contexts.
5. A dosemeter fitted to an employee for 2 hours gives an LAeq reading of 89.2 db. If the actual working time of the employee is 10 hours, calculate his daily personal noise exposure (LEP,d). State any assumptions you have made in making your calculation.
6. A noise is found to be strongly dominated by tones at 500Hz and 2000Hz, with unweighted octave band levels at these frequencies of 95 and 92 dB respectively. Determine the A-weighted sound pressure level that would be produced by this noise.
7. Give a simple noise control technique that could be applied where the noise was generated by hard objects falling in to a metal chute. Outline why technique is effective.
8. Outline and explain one difficulty in assessing the noise risk from the use of a powered hand tool, such as a power drill used by a construction worker.
9. Estimate the effective noise level experienced if wearing a hearing protector with SNR of 26 dB in a noise environment with LC = 96 dB and LA = 94 dB.
10. A worker spends 45 minutes of the day exposed to noise with an LAeq of 92 dB. What restrictions on noise exposure must be in place regarding the other 7 hours of her working day if her daily exposure (LEP,d ) is to be below 85 dB?
(Answer TWO questions only 20 marks are available for each question)
1 (a) Explain what is meant by ‘overprotection’ in the context of personal hearing protection. Discuss why overprotection is to be avoided in an occupational noise situation. [5 marks]
1 (b) Calculate, by the standard method, the effective A-weighted sound pressure level at the ear if the following protector is worn in the noise environment shown. Comment on the suitability of the protector. [8 marks]
|Octave band centre frequency|
|Protector assumed protection (dB)||3||5||13||21||26||33||38|
|Noise environment (dB)||97||93||92||96||99||100||91|
1 (c) Describe in outline the topics and items you would cover if asked to provide a session of information, instruction and training for employees in personal hearing protection. [7 marks]
2 (a) You are asked by a company to audit its performance in the areas of personal hearing protection and worker hearing conversation. Describe the observations you would make and the information you would gather, both on the factory floor and in the offices, in order to carry out your audit. Outline the criteria you would apply to the various aspects in order to judge the success, or otherwise, of the company’s performance. [12 marks]
2 (b) A worker for his company spends ½ hour of the day in a noisy environment, where you measure representative noise levels of LAeq= 100dB, and LCeq = 103 dB. The worker spends the rest of the day exposed to sound levels equivalent to an LAeq of 75 dB.
You are asked to give advice on selection of hearing protection for this worker. Two different hearing protection for this worker. Two different hearing protection devices are availbale, with the characteristics shown below. Estimate the likely protection afforded by each device in the ‘real world’, and comment on the suitability of each for this worker. [8 marks]
Attenuation value (dB)