5.3 Physical Hazards: Noise, Hearing Conservation & Radiation

Physical Hazards: Noise and Radiation

Physical hazards involve environmental factors that can harm the body without necessarily touching it. The most prevalent physical hazards managed by Occupational Hygiene and Safety Technicians are hazardous noise levels and radiation exposure.

Occupational Noise Exposure

Exposure to high levels of noise can lead to Noise-Induced Hearing Loss (NIHL), which is permanent, painless, and progressive. It typically begins with a loss of high-frequency hearing and eventually impairs the ability to understand speech.

Measuring Noise

Sound pressure levels are measured in decibels (dB). For occupational settings, measurements are taken on the A-weighted scale (dBA). The A-weighting network mimics the sensitivity of the human ear, which is less sensitive to very low and very high frequencies.

OSHA Limits and the Exchange Rate

OSHA's standard (29 CFR 1910.95) establishes specific limits for noise exposure based on an 8-hour time-weighted average:

• Permissible Exposure Limit (PEL): 90 dBA. Exposures above this limit are illegal without implementing engineering controls, administrative controls, or mandatory hearing protection.
• Action Level (AL): 85 dBA. If exposures reach or exceed this level, the employer must implement a comprehensive Hearing Conservation Program.

The 5 dB Exchange Rate: OSHA utilizes a 5 dB exchange rate (also known as the doubling rate). This means that for every 5 dBA increase in the noise level, the allowed exposure time is reduced by half.

(Note: NIOSH and ACGIH recommend a more protective 3 dB exchange rate and an 85 dBA exposure limit, but OSHA enforces the 5 dB rate.)

The Hearing Conservation Program (HCP)

When exposures hit the 85 dBA Action Level, an HCP must include:

1. Monitoring: Regular assessment of noise levels.
2. Audiometric Testing: Baseline and annual hearing tests to monitor for Standard Threshold Shifts (STS).
3. Hearing Protectors: Provided free of charge to employees.
4. Training: Annual training on noise hazards and protector use.
5. Recordkeeping: Maintaining exposure and audiometric records.

Calculating Hearing Protection: The NRR

Hearing protectors (earplugs, earmuffs) are rated with a Noise Reduction Rating (NRR) by the EPA. However, laboratory NRR values significantly overestimate real-world protection due to improper fit and usage by workers.

When evaluating hearing protectors in the field using A-weighted noise measurements, OSHA requires a specific "derating" calculation to estimate actual protection:

Estimated Field Protection = (NRR - 7) / 2

Example Calculation: A worker is exposed to an environment measuring 100 dBA. They are wearing earplugs with an NRR of 27.

1. Subtract 7 from the NRR: 27 - 7 = 20
2. Divide by 2: 20 / 2 = 10 dB of actual protection.
3. Subtract the protection from the exposure: 100 dBA - 10 dB = 90 dBA effective exposure. The worker's effective exposure is right at the 90 dBA PEL.

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Radiation Hazards

Radiation is energy traveling through space. In occupational health, it is categorized into two types based on its energy level: ionizing and non-ionizing.

Non-Ionizing Radiation

This radiation has enough energy to move atoms or cause them to vibrate, but not enough to remove electrons. The primary hazard is tissue heating.

• Examples: Radio waves, microwaves, infrared, visible light, and ultraviolet (UV).
• Occupational sources: Welding arcs (UV/IR), lasers, microwave communication towers, industrial heating.
• Hazards: Skin burns, eye damage (e.g., cataracts, arc eye/welder's flash).

Ionizing Radiation

Ionizing radiation has high energy capable of knocking electrons out of their orbits, ionizing atoms. This ionization damages living cells and DNA, leading to mutations, acute radiation sickness, and cancer.

There are four primary types of ionizing radiation:

1. Alpha Particles (α): Heavy, highly charged particles. They have very low penetrating power and can be stopped by a sheet of paper or the dead outer layer of human skin. However, if an alpha-emitting substance is inhaled or ingested, it is highly dangerous because it delivers all its energy to internal tissues.
2. Beta Particles (β): Electrons emitted from the nucleus. More penetrating than alpha, they can pass through the dead skin layer to live tissue. They are stopped by a thin sheet of plastic, glass, or aluminum.
3. Gamma Rays (γ) and X-Rays: Electromagnetic radiation (photons) with no mass or charge. They are highly penetrating and can pass completely through the human body. Stopping them requires dense shielding, such as thick lead or concrete.
4. Neutrons: Uncharged particles emitted during nuclear fission. They are highly penetrating and require hydrogen-rich materials (like water, concrete, or plastics) for shielding.

Radiation Protection: ALARA

The guiding philosophy for radiation protection is ALARA: As Low As Reasonably Achievable. The goal is to minimize radiation exposure to the absolute lowest practical level.

To achieve ALARA, technicians rely on three fundamental principles of external radiation protection:

1. Time: Minimize the duration of exposure. Dose is directly proportional to time (Dose = Dose Rate × Time). Cutting exposure time in half cuts the dose in half.
2. Distance: Maximize the distance from the source. Radiation intensity follows the Inverse Square Law. If you double your distance from a point source, the radiation intensity drops to one-quarter (1/4) of the original amount.
3. Shielding: Place dense materials between the worker and the source. The type of shielding depends on the radiation (e.g., lead for gamma, plastic for beta).