Lex, Leq, T And Dose. (2 Marks)
a. Why did you choose these settings? (2 marks)
The settings were based on the Canadian Safety Association (CSA Standard Z107.56) requirements and American Conference of Governmental Industrial Hygienist (ACGIH). Also the Alberta exchange rate is 3 dB based on the Alberta OHS Code. The criterion level was set at 85 dB based on the Alberta 8 hour occupational exposure level for noise.
2. Explain the difference between Lex,, Leq,t and Dose. (6 marks)
LexT, - is the level of a worker’s total exposure to noise in dBA, averaged over the entire shift length or workday and adjusted to an equivalent 8 hour exposure based on a 3dB exchange rate. It always reflects the sound level for an 8 hour work day. This parameter also allows for a comparison …show more content…
between measured occupation sound levels and the legislated 8 hour allowable occupational exposure level for noise. The LexT is derived from the measurement Leq,t by a simple adjustment to account for the effects of longer or shorter working days on workers hearing. It is also referred to as the calculated noise exposure level for a prescribed time period, T.
Leq,t is the average sound level measured over the run time, when the exchange rate is set to 3dB and the threshold is off. Unlike the Lex, it reflects the equivalent sound level over a sampling period of t hours. In this case, t could be 4, 6, 8, 10, 12 hours as the case may be.
Dose is related to the criterion level which is 85dB for Alberta A dose weighing of 100%. It is defined as the maximum allowable exposure to accumulated noise. The daily dose should not exceed 100. The exchange rate for Alberta is 3dB, this implies that for every 3dB decrease in sound pressure level, the dose reduces by 50% i.e. a 50% dose represents the action level and is equal to 82dB.
3. Determine the Lex of a 4 hour personal noise sample that resulted in an exposure of 91 dBA. (8 marks)
Lex,T = Leq,t + 10 log (t/T)
Lex, T = 91dBA + 10 log (4hr/8hr) = 87.98dB = 88dBA.
a. Based on the OHS Code, was the worker overexposed? Why or why not? (2 marks)
Yes the worker was over exposed because the legislated exposure level for an 8 hour work shift for Alberta is 85dBA. For a noise level of 91 dBA, the allowable noise exposure duration should be 2 hours.
4. Determine the dose of a personal noise sample taken, assuming the noise exposure has been consistent at 83 dBA throughout the day. (8 marks)
Daily Noise Dose = 100 (C/T); T is the referenced allowed duration for 83dBA which is 12.68hrs
Daily Noise Dose = 100 (8/12.68) = 63.1%
a.
Would you consider this employee to be overexposed? Why or why not? (2 marks)
No, the worker was not overexposed because the dose of 62.9% was below the criterion level of 85dBA which is a 100% dose level.
However, the calculated dose of 62.9% was above the action level of 50% which means that a noise monitoring program should be established and controls (engineering, administrative or personal protective equipment as a last resort) should be put in place to further reduce the dose level to below the action level.
5. List and explain two environmental limitations each, of the Sound Level Meter, and the Noise Dosimeter, based on the users’ instruction manual. (8 marks)
Sound level meter
1. The relative humidity should be between 10 – 90% non-condensing. The amount of water vapour in the air during the testing period needs to be taken into consideration as this can affect the functionality of the …show more content…
equipment.
2. There is a less than ±0.5dB effect over an operating temperature of -10 °C to +50 °C. This implies that the equipment will not function properly at temperature below -10°C or above +50°C. The operational functionality of the equipment can be affected by the extreme temperatures of the winter where the atmospheric temperature can fall below -10 °C. Hence sampling of noise should be scheduled during the summer, spring or fall seasons to prevent errors in the data. If sampling has to be done in the winter, then a sound level meter without this limitation should be used.
Noise Dosimeter
1.
The humidity for operation is 0 – 95% non-condensing. The amount of water vapour in the air during the testing period needs to be taken into consideration as this can affect the functionality of the equipment.
2. The operating temperature is -10 °C to +50 °C. This implies that the equipment will not function properly at temperature below -10°C or above +50°C .The operational functionality of the equipment can be affected by the extreme temperatures of the winter where the atmospheric temperature can fall below -10 °C. Hence sampling of noise should be scheduled during the summer, spring or fall seasons to prevent errors in the data. If sampling has to be done in the winter, then a sound level meter without this limitation should be used.
6. Based on the OHS Code, if a Noise Exposure Assessment confirms that workers are exposed to excess noise at a work site, what would be the next step an employer must take? (2 marks)
The employer must develop and implement a noise management program (also called a hearing conservation program). The program procedures should be writing and made available to the workers. The program must include the following seven components:
1. Worker
education
2. Measuring or monitoring worker exposure to noise
3. Posting warning signs in any work area where the noise level exceeds 85dBA
4. Use of noise control methods
5. Selection, use and maintenance of hearing protection devices
6. Audiometric testing
7. Annual program review
7. Provide two examples from your monitoring, of where your noise levels were high. Provide one recommendation, for each example, to reduce the noise levels. Use recommended controls from at least two different levels of the hierarchy. (8 marks)
Two examples where the noise levels were high on the noise map where the Bay 1 (Hollow core area) with a sound level of 73.2dB and the crane way with a sound level of 80.1dB. However, both readings where below the action level (82dB), strict recommendations to reduce the sound level are not needed. Suggested controls to reduce these levels further are stated below.
Crane way - Engineering Controls:
Substitution – to replace the noisy overhead crane, machinery or processes with quieter ones
Isolation – segregating the noisy areas with sound barriers and partitions, using sound absorbent material to cover the pathway of the overhead cranes while in operation or by placing the equipment in an enclosure.
Bay 1 (Hollow core area) – Administrative Controls:
Administrative controls can be used to limit entry to the hollow-core area to authorised personnel or workers who have a task to perform in the area. Work rotations by employee can also be scheduled. Noise signage can also be posted to create awareness. Where the engineering and administrative controls cannot reduce the noise or where they are not reasonable practicable, the employer must provide workers and visitors with hearing protection e.g. ear muffs or ear plugs based on the sound level and Alberta code specifications.
8. If your noise monitoring yielded a Leq of 96 dBA, and your employee was wearing earplugs with a NRR of 33 dB, based on CSA Z94.2, Table 2, demonstrate and state whether they would be sufficiently protected from overexposure during an 8 hour workday? (8 marks)
Earplugs Noise exposure = Leq - (NRR (0.5)-3) = 96 – (33(0.5)-3) = 82.5dBA
Yes, the worker will be sufficiently protected from overexposure during an 8-hour workday because the noise exposure with the ear plugs will be 82.5dBA, which is below the 85dBA allowable exposure level for an 8-hour work day.
However, 82.5dBA is slightly above the action level (50%=82dBA) hence further effort to monitor the noise exposure levels is needed. There is also a need to improve the existing controls (engineering and administrative) to reduce the sound level to below the 82dBA. To monitor the effectiveness of the control, a health surveillance program will be recommended. In this case, a baseline test will be completed and a repeat audiometric testing schedule 1 year after the initial baseline test and subsequently every 2 years (Alberta OHS Code, 2009).
9. While completing your area sampling, you noted two very loud pieces of equipment, and a worker who was standing between the two pieces working. The reading from the first piece was 83 dBA, and the second was 84 dBA. What is the combined sound pressure level for the two machines? (8 marks)
SPLtotal = 10 log (1083/10 +1084/10) = 10log (1.99x108+2.51x108) = 86.5dBA
a. Based on the OHS Code, how long could the worker work in this area without being overexposed? (2 marks)
Based on this result, the worker is over exposed to noise if he worked an 8 hour work day.
For an 87dBA exposure level the worker can work for a 5.0hour work day.
The settings were based on the Canadian Safety Association (CSA Standard Z107.56) requirements and American Conference of Governmental Industrial Hygienist (ACGIH). Also the Alberta exchange rate is 3 dB based on the Alberta OHS Code. The criterion level was set at 85 dB based on the Alberta 8 hour occupational exposure level for noise.
2. Explain the difference between Lex,, Leq,t and Dose. (6 marks)
LexT, - is the level of a worker’s total exposure to noise in dBA, averaged over the entire shift length or workday and adjusted to an equivalent 8 hour exposure based on a 3dB exchange rate. It always reflects the sound level for an 8 hour work day. This parameter also allows for a comparison …show more content…
between measured occupation sound levels and the legislated 8 hour allowable occupational exposure level for noise. The LexT is derived from the measurement Leq,t by a simple adjustment to account for the effects of longer or shorter working days on workers hearing. It is also referred to as the calculated noise exposure level for a prescribed time period, T.
Leq,t is the average sound level measured over the run time, when the exchange rate is set to 3dB and the threshold is off. Unlike the Lex, it reflects the equivalent sound level over a sampling period of t hours. In this case, t could be 4, 6, 8, 10, 12 hours as the case may be.
Dose is related to the criterion level which is 85dB for Alberta A dose weighing of 100%. It is defined as the maximum allowable exposure to accumulated noise. The daily dose should not exceed 100. The exchange rate for Alberta is 3dB, this implies that for every 3dB decrease in sound pressure level, the dose reduces by 50% i.e. a 50% dose represents the action level and is equal to 82dB.
3. Determine the Lex of a 4 hour personal noise sample that resulted in an exposure of 91 dBA. (8 marks)
Lex,T = Leq,t + 10 log (t/T)
Lex, T = 91dBA + 10 log (4hr/8hr) = 87.98dB = 88dBA.
a. Based on the OHS Code, was the worker overexposed? Why or why not? (2 marks)
Yes the worker was over exposed because the legislated exposure level for an 8 hour work shift for Alberta is 85dBA. For a noise level of 91 dBA, the allowable noise exposure duration should be 2 hours.
4. Determine the dose of a personal noise sample taken, assuming the noise exposure has been consistent at 83 dBA throughout the day. (8 marks)
Daily Noise Dose = 100 (C/T); T is the referenced allowed duration for 83dBA which is 12.68hrs
Daily Noise Dose = 100 (8/12.68) = 63.1%
a.
Would you consider this employee to be overexposed? Why or why not? (2 marks)
No, the worker was not overexposed because the dose of 62.9% was below the criterion level of 85dBA which is a 100% dose level.
However, the calculated dose of 62.9% was above the action level of 50% which means that a noise monitoring program should be established and controls (engineering, administrative or personal protective equipment as a last resort) should be put in place to further reduce the dose level to below the action level.
5. List and explain two environmental limitations each, of the Sound Level Meter, and the Noise Dosimeter, based on the users’ instruction manual. (8 marks)
Sound level meter
1. The relative humidity should be between 10 – 90% non-condensing. The amount of water vapour in the air during the testing period needs to be taken into consideration as this can affect the functionality of the …show more content…
equipment.
2. There is a less than ±0.5dB effect over an operating temperature of -10 °C to +50 °C. This implies that the equipment will not function properly at temperature below -10°C or above +50°C. The operational functionality of the equipment can be affected by the extreme temperatures of the winter where the atmospheric temperature can fall below -10 °C. Hence sampling of noise should be scheduled during the summer, spring or fall seasons to prevent errors in the data. If sampling has to be done in the winter, then a sound level meter without this limitation should be used.
Noise Dosimeter
1.
The humidity for operation is 0 – 95% non-condensing. The amount of water vapour in the air during the testing period needs to be taken into consideration as this can affect the functionality of the equipment.
2. The operating temperature is -10 °C to +50 °C. This implies that the equipment will not function properly at temperature below -10°C or above +50°C .The operational functionality of the equipment can be affected by the extreme temperatures of the winter where the atmospheric temperature can fall below -10 °C. Hence sampling of noise should be scheduled during the summer, spring or fall seasons to prevent errors in the data. If sampling has to be done in the winter, then a sound level meter without this limitation should be used.
6. Based on the OHS Code, if a Noise Exposure Assessment confirms that workers are exposed to excess noise at a work site, what would be the next step an employer must take? (2 marks)
The employer must develop and implement a noise management program (also called a hearing conservation program). The program procedures should be writing and made available to the workers. The program must include the following seven components:
1. Worker
education
2. Measuring or monitoring worker exposure to noise
3. Posting warning signs in any work area where the noise level exceeds 85dBA
4. Use of noise control methods
5. Selection, use and maintenance of hearing protection devices
6. Audiometric testing
7. Annual program review
7. Provide two examples from your monitoring, of where your noise levels were high. Provide one recommendation, for each example, to reduce the noise levels. Use recommended controls from at least two different levels of the hierarchy. (8 marks)
Two examples where the noise levels were high on the noise map where the Bay 1 (Hollow core area) with a sound level of 73.2dB and the crane way with a sound level of 80.1dB. However, both readings where below the action level (82dB), strict recommendations to reduce the sound level are not needed. Suggested controls to reduce these levels further are stated below.
Crane way - Engineering Controls:
Substitution – to replace the noisy overhead crane, machinery or processes with quieter ones
Isolation – segregating the noisy areas with sound barriers and partitions, using sound absorbent material to cover the pathway of the overhead cranes while in operation or by placing the equipment in an enclosure.
Bay 1 (Hollow core area) – Administrative Controls:
Administrative controls can be used to limit entry to the hollow-core area to authorised personnel or workers who have a task to perform in the area. Work rotations by employee can also be scheduled. Noise signage can also be posted to create awareness. Where the engineering and administrative controls cannot reduce the noise or where they are not reasonable practicable, the employer must provide workers and visitors with hearing protection e.g. ear muffs or ear plugs based on the sound level and Alberta code specifications.
8. If your noise monitoring yielded a Leq of 96 dBA, and your employee was wearing earplugs with a NRR of 33 dB, based on CSA Z94.2, Table 2, demonstrate and state whether they would be sufficiently protected from overexposure during an 8 hour workday? (8 marks)
Earplugs Noise exposure = Leq - (NRR (0.5)-3) = 96 – (33(0.5)-3) = 82.5dBA
Yes, the worker will be sufficiently protected from overexposure during an 8-hour workday because the noise exposure with the ear plugs will be 82.5dBA, which is below the 85dBA allowable exposure level for an 8-hour work day.
However, 82.5dBA is slightly above the action level (50%=82dBA) hence further effort to monitor the noise exposure levels is needed. There is also a need to improve the existing controls (engineering and administrative) to reduce the sound level to below the 82dBA. To monitor the effectiveness of the control, a health surveillance program will be recommended. In this case, a baseline test will be completed and a repeat audiometric testing schedule 1 year after the initial baseline test and subsequently every 2 years (Alberta OHS Code, 2009).
9. While completing your area sampling, you noted two very loud pieces of equipment, and a worker who was standing between the two pieces working. The reading from the first piece was 83 dBA, and the second was 84 dBA. What is the combined sound pressure level for the two machines? (8 marks)
SPLtotal = 10 log (1083/10 +1084/10) = 10log (1.99x108+2.51x108) = 86.5dBA
a. Based on the OHS Code, how long could the worker work in this area without being overexposed? (2 marks)
Based on this result, the worker is over exposed to noise if he worked an 8 hour work day.
For an 87dBA exposure level the worker can work for a 5.0hour work day.