CIH - Certified Industrial Hygienist Physical Agents: Noise and Radiation 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?

Accepted Answer

85 dBA

Answer

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?

Accepted Answer

Alpha radiation

Answer

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)?

Accepted 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.

Answer

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?

Accepted Answer

8 mR/hr

Answer

The inverse square law states that intensity is inversely proportional to the square of the distance (I₁d₁² = I₂d₂²). Here, the distance increased by a factor of 4 (12 ft / 3 ft = 4). Therefore, the intensity will decrease by a factor of 4², 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?

Accepted Answer

Applying a layer of viscoelastic damping material directly to the panel.

Answer

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.

CIH - Certified Industrial Hygienist Exam Practice Test

CIH - Certified Industrial Hygienist Exam Practice Test

CIH - Certified Industrial Hygienist Physical Agents: Noise and Radiation Questions and Answers