8.4 Physical Hazards, Hearing Conservation, Radiation, Heat, and Vibration

Health Hazards Beyond Chemicals

Physical hazards arise from energy or environment: noise, vibration, heat, cold, ionizing and non-ionizing radiation, pressure, and lighting. The ASP tests the key thresholds and the program elements that control each.

Hearing Conservation — Memorize the Numbers

OSHA's occupational noise standard, 29 CFR 1910.95, drives most exam questions. Three numbers are non-negotiable:

With the 5 dB exchange rate, the permissible duration is 8 hours at 90 dBA, 4 hours at 95 dBA, and 2 hours at 100 dBA. A complete program includes noise monitoring, audiometric testing (baseline and annual), hearing protection availability, training, and recordkeeping. A Standard Threshold Shift (STS) is an average change of 10 dB or more at 2000, 3000, and 4000 Hz in either ear relative to baseline — a key trigger for follow-up. Note that ACGIH/NIOSH recommend a more protective 3 dB exchange rate; the exam may ask you to distinguish OSHA (5 dB) from NIOSH (3 dB).

Radiation: Time, Distance, Shielding, ALARA

Ionizing radiation (alpha, beta, gamma, X-ray, neutron) has enough energy to strip electrons and damage DNA. Protection rests on three engineering levers — minimize time near the source, maximize distance (dose falls with the inverse-square law, so doubling distance cuts dose to one-fourth), and add shielding matched to the radiation type (dense material such as lead for gamma; hydrogen-rich material for neutrons). The overarching philosophy is ALARA — As Low As Reasonably Achievable.

Non-ionizing radiation (ultraviolet, visible, infrared, microwave, radiofrequency, lasers) lacks ionizing energy; controls are enclosure, interlocks, filters, and procedure, tailored to the affected tissue (skin and eye for UV/laser).

Thermal Stress

Heat stress is assessed with Wet Bulb Globe Temperature (WBGT), which combines air temperature, humidity, radiant heat, and air movement into a single index compared against work-rest guidance. Controls follow a clear order:

• Acclimatization — gradually building heat tolerance over 7–14 days; new and returning workers are at highest risk.
• Hydration — small, frequent water intake.
• Work-rest cycles and shaded or air-conditioned recovery areas.
• Engineering — ventilation, shielding from radiant sources, cooling.

Heat illness ranges from cramps and exhaustion to heat stroke, a medical emergency. Cold stress brings different concerns — wind chill, wet clothing, contact with cold surfaces, and reduced dexterity — managed with insulating dry layers, warming breaks, and monitoring.

Vibration

Hand-arm vibration (HAV) from powered tools can cause vibration white finger (Raynaud's phenomenon); whole-body vibration from vehicles is linked to low-back disorders. Controls include lower-vibration tools, equipment maintenance, anti-vibration mounts and seating, limiting exposure duration, and early symptom reporting. Padded gloves add comfort but are not a complete control.

A Worked Noise-Dose Example

Noise dose is the percentage of the daily permissible exposure used up. A 100% dose corresponds to the 90 dBA PEL for 8 hours. Suppose a machinist spends 4 hours at 95 dBA. Using OSHA's 5 dB exchange rate, the permitted time at 95 dBA is 4 hours, so 4 hours of actual exposure equals a 100% dose — already at the PEL with no margin. Add even 1 hour at 100 dBA (permitted time 2 hours, contributing 50%) and the combined dose is 150%, an overexposure requiring engineering or administrative controls and mandatory hearing protection. The exam may give partial exposures and ask you to sum the dose fractions.

Choosing Hearing Protection

Hearing protectors carry a Noise Reduction Rating (NRR) in decibels. OSHA derates the labeled NRR for real-world fit; a common method subtracts 7 from the NRR, then halves the result for actual attenuation under the 8-hour TWA. A worker exposed to 100 dBA with a 33-NRR muff gets roughly (33 - 7)/2 = 13 dB of usable protection, landing near 87 dBA — protected but with little spare margin. Selection must also avoid overprotection, which can isolate a worker from warning signals and speech.

Common Physical-Hazard Traps

• Mixing up the 85 dBA action level (program trigger) with the 90 dBA PEL (engineering-control trigger).
• Applying OSHA's 5 dB exchange rate when a question specifies NIOSH (3 dB).
• Forgetting that radiation distance follows the inverse-square law (double distance, quarter dose).
• Treating heat stress as comfort rather than a WBGT-quantified hazard with a defined work-rest schedule.
• Assuming a high Noise Reduction Rating equals full real-world protection — the labeled NRR must be derated for fit.
• Overlooking that overprotection from hearing devices can mask alarms and speech, creating a new safety risk.

Remember that non-ionizing radiation still injures tissue at the point of contact: ultraviolet light burns the cornea and skin, infrared causes thermal eye damage, and lasers can permanently injure the retina even at low average power. Controls differ from ionizing radiation — enclosure, filtered eyewear matched to the wavelength, beam interlocks, and warning signage rather than lead shielding.

For program-level ASP questions, prefer source reduction and engineering controls, then administrative controls and PPE, and always pair progressive hazards — noise, heat susceptibility, vibration — with appropriate medical or occupational-health follow-up such as audiometry or symptom monitoring.