Respiratory protection is required when silica exposure exceeds what threshold?
Correct Answer
B) PEL of 50 μg/m³
OSHA 29 CFR 1926.1153 requires respiratory protection when employee exposure exceeds the Permissible Exposure Limit (PEL) of 50 μg/m³ averaged over an 8-hour day.
Why This Is the Correct Answer
OSHA 29 CFR 1926.1153 (Respirable Crystalline Silica standard for construction) mandates respiratory protection when an employee's 8-hour TWA exposure exceeds the Permissible Exposure Limit (PEL) of 50 μg/m³. Above this threshold, engineering controls alone may not be sufficient, so respiratory protection becomes a required additional safeguard.
Why the Other Options Are Wrong
Option A: 100 μg/m³
100 μg/m³ is not an OSHA-defined trigger for respiratory protection under the silica standard. It is twice the PEL and would represent dangerously uncontrolled exposure.
Option C: Action level of 25 μg/m³
25 μg/m³ is the Action Level (AL) under OSHA's silica rule. At the AL, employers must begin medical surveillance and exposure assessment, but respiratory protection is not yet mandatory — that requirement kicks in only above the 50 μg/m³ PEL.
Option D: 200 μg/m³
200 μg/m³ has no regulatory significance under OSHA's silica standard. Selecting this answer confuses a made-up number with an actual threshold.
Memory Technique
Think '50 = Protect': the PEL is 50 μg/m³ and that's the point where you must Protect your lungs with a respirator. The AL at 25 is half of 50 — half-way there means 'Alert but not yet respirator required.'
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