A concrete finisher is working with wet concrete containing crystalline silica. The exposure assessment shows an 8-hour TWA of 60 μg/m³. What is required based on OSHA's respirable crystalline silica standard?
Correct Answer
D) N95 filtering facepiece respirator minimum
OSHA's crystalline silica standard has an action level of 25 μg/m³ and PEL of 50 μg/m³. At 60 μg/m³, respiratory protection is required, with N95 being the minimum acceptable for this exposure level.
Why This Is the Correct Answer
OSHA's respirable crystalline silica standard (29 CFR 1926.1153) sets the PEL at 50 μg/m³ as an 8-hour TWA. At 60 μg/m³, the exposure exceeds the PEL, requiring respiratory protection. For exposures up to 10 times the PEL (500 μg/m³), an N95 filtering facepiece respirator provides adequate protection with its assigned protection factor of 10. This makes N95 the minimum acceptable respiratory protection for this exposure level.
Why the Other Options Are Wrong
Option A: Supplied air respirator required
Supplied air respirators are required only for very high exposures exceeding 500 μg/m³ (10 times the PEL) or in oxygen-deficient atmospheres. At 60 μg/m³, this level of protection is excessive and unnecessarily burdensome for workers when simpler respiratory protection like N95 masks can adequately protect against the exposure.
Option B: No respiratory protection required
The exposure of 60 μg/m³ exceeds OSHA's PEL of 50 μg/m³ for respirable crystalline silica. When workplace exposures exceed the PEL, respiratory protection is mandatory under OSHA standards. Additionally, this exposure also exceeds the action level of 25 μg/m³, which triggers additional requirements including medical surveillance and training.
Option C: Half-face elastomeric respirator with P100 filters
While half-face elastomeric respirators with P100 filters provide excellent protection against crystalline silica, they exceed the minimum requirement for this exposure level. At 60 μg/m³, an N95 filtering facepiece respirator provides adequate protection. Using higher-level protection than necessary increases costs and worker burden without additional safety benefit.
Memory Technique
Remember 'Fifty-Five-Ten': PEL is 50, this exposure is 60 (just over), so N95 with protection factor of 10 works fine.
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