CIH - Certified Industrial Hygienist Physical Agents: Noise and Radiation Questions and Answers ā Questions and Answers
Question 1: A worker's 8-hour Time-Weighted Average (TWA) noise exposure is 90 dBA. The employer modifies the job so the worker spends only 4 hours performing this task and the remaining 4 hours in a quiet office with negligible noise levels (<80 dBA). Using the OSHA 5-dB exchange rate, what is the worker's new 8-hour TWA?
- 95 dBA
- 90 dBA
- 87 dBA
- 85 dBA (Correct answer)
Correct answer: 85 dBA
According to the OSHA 5-dB exchange rate, an 8-hour exposure at 90 dBA is equivalent to a 100% dose. If the exposure time at that level is halved to 4 hours, the dose is also halved to 50%. The formula to convert dose back to an 8-hour TWA is: TWA = 16.61 * log10(Dose/100) + 90. For a 50% dose: TWA = 16.61 * log10(0.5) + 90 = 16.61 * (-0.301) + 90 = -5 + 90 = 85 dBA.
Question 2: Which of the following types of ionizing radiation consists of heavy, positively charged particles and is most easily stopped by a sheet of paper or the outer layer of skin?
- Beta radiation
- Gamma radiation
- Alpha radiation (Correct answer)
- Neutron radiation
Correct answer: Alpha radiation
Alpha particles are relatively large, consisting of two protons and two neutrons, giving them a +2 charge. Due to their size and charge, they interact readily with matter, losing their energy quickly. This makes them unable to penetrate even thin materials like paper or the outermost dead layer of skin.
Question 3: According to the OSHA Occupational Noise Exposure standard (29 CFR 1910.95), which of the following defines a Standard Threshold Shift (STS)?
- A 15 dB change in hearing threshold at any single test frequency compared to the baseline audiogram.
- A change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear. (Correct answer)
- Any work-related, permanent hearing loss confirmed by a physician.
- An average change of 10 dB or more at 500, 1000, and 2000 Hz that is confirmed by a retest within 30 days.
Correct answer: A change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear.
The OSHA regulation at 29 CFR 1910.95(g)(10)(i) explicitly defines a Standard Threshold Shift (STS) as 'a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear'.
Question 4: The radiation intensity measured 3 feet from a point source is 128 mR/hr. If a worker moves to a position 12 feet from the source, what will the new radiation intensity be, according to the inverse square law?
- 32 mR/hr
- 8 mR/hr (Correct answer)
- 16 mR/hr
- 64 mR/hr
Correct answer: 8 mR/hr
The inverse square law states that intensity is inversely proportional to the square of the distance (IādāĀ² = IādāĀ²). Here, the distance increased by a factor of 4 (12 ft / 3 ft = 4). Therefore, the intensity will decrease by a factor of 4Ā², which is 16. The new intensity will be 128 mR/hr / 16 = 8 mR/hr.
Question 5: A large, thin metal guard on a machine is vibrating excessively, creating a significant source of tonal noise. Which of the following engineering controls would be MOST effective for specifically reducing the noise radiated by this vibrating panel?
- Installing sound-absorbing foam on the walls of the room.
- Constructing a full acoustical enclosure around the entire machine.
- Applying a layer of viscoelastic damping material directly to the panel. (Correct answer)
- Providing the operator with high-attenuation earmuffs.
Correct answer: Applying a layer of viscoelastic damping material directly to the panel.
Damping is the process of converting vibrational energy into heat, thereby reducing the amplitude of the vibration and the resulting sound. Applying a viscoelastic material directly to the vibrating panel is a damping treatment that addresses the root cause of the noise at the source. Sound absorption on the walls treats the room's acoustics, an enclosure is a barrier control, and earmuffs are PPE, not an engineering control.
Question 6: The guiding principle of radiation protection that advocates for keeping radiation doses as far below the specified limits as is practical, considering social, economic, and technical factors, is known as:
- The Inverse Square Law
- ALARA (As Low As Reasonably Achievable) (Correct answer)
- The Dose-Response Relationship
- The Half-Value Layer Principle
Correct answer: ALARA (As Low As Reasonably Achievable)
ALARA, which stands for "As Low As Reasonably Achievable," is the cornerstone philosophy of radiation protection programs. It means that even if a planned dose is below the regulatory limit, efforts should be made to reduce it further through practical means like optimizing time, distance, and shielding.
CIH - Certified Industrial Hygienist Physical Agents: Noise and Radiation Questions and Answers
A worker's 8-hour Time-Weighted Average (TWA) noise exposure is 90 dBA.
The employer modifies the job so the worker spends only 4 hours performing this task and the remaining 4 hours in a quiet office with negligible noise levels (<80 dBA).
Using the OSHA 5-dB exchange rate, what is the worker's new 8-hour TWA?