Question 4 [30 marks] (a) An employee has two main tasks throughout the day oper

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Question 4 [30 marks] (a) An employee has two main tasks throughout the day operating a lathe and performing administrative duties in an office. You measure the noise levels in the office at an LAeq,15mins 55 dB(A). The noise level in the office rarely fluctuates above this. An operation on the lather typically lasts for 15 minutes, with an LAeq, 15mins of 97 dB(A). Assuming the employee spends all his time in the office when he is not operating the lathe, how many times can the employee operate the lathe without the need for noise protection under OSHA regulations? [10 points] (b) Re-calculate how many times the employee may operate the lathe if the criterion level is reduced to 85 dB(A) and the exchange rate is changed to 3 dB(A) [S points] (c)List two advantages and two disadvantages of earplugs [S points] (d) The duties of the employee in the situation above are changed. Now the employee will have the following noise exposure: 105 dB(A) for 1.5 hours, 90 dB(A) for 1 hour, 88 dB(A) for 4 hours, 75 dB(A) for 1.5 hours and 73dB(A) for 0.5 hours. (i) Find the Noise Dose (in %) for the employee. (ii) How much time could the employee spend at the first task (at 105 dB(A) without exceeding his allowable exposure during the workday (under OSHA regulations)? Assume no change in other tasks. [10 points

Explanation / Answer

Ans 1 - The permissible noise levels at 97dB according to OSHA is 3 hours. Hence the no. of times a lathe can be operated is

n = 3x60 / 15 = 12 times.

Ans 2: The criteria level of 85 dB (A) and exchange rate of 3 dBA is recommended as protective measures for 8 hours, so the machine can be operated for any length of time in 8 hours shift.

Ans 3: Advantages of earplugs

(a) Reduction in exposure to noise

(b) Ease of use and portability.

Disadvatages

(a) Difficulty for user in hot and humid evironment.

(c) May cause accidents at workplace due to compromised hearing ability.

Ans 4:

Permissible limits for 105 dB = 1hr

    Permissible limits for 90 dB = 8 hrs

    Permissible limits for 88 dB and below= No limit

Dose of noise = Time spent/ max. time allowed at a dB level + Time spent / Max time allowed at second dB level +...... Time spent / Max. time allowed at nth dB level.

= 1.5/1+1/8 +( 4+1.5+0.5)/ infinite

= 1.5+0.125 =1.625

= 162.5%

(ii)An employee can spend only one hour at the first task which is his limit for exposure during one work day.

  

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