What is the protection factor for a respirator with HEPA filters?

• A. 5 OEL
• B. 20 OEL
• C. 50 OEL
• D. 10 OEL

Answer: (D)

Protection factor is how much a respirator lowers the amount of contaminant you inhale compared with breathing the air directly outside. For a respirator with HEPA filters, the value used here is ten, meaning it reduces inhaled concentration to one-tenth of the ambient level. When you relate this to the occupational exposure limit (OEL), the respirator provides a protection of 10 OEL — it cuts exposure by a factor of ten relative to the allowed limit. For example, if the OEL is 0.05 units, wearing the HEPA respirator would keep your inhaled concentration around 0.005 units. That is why the correct option reflects a protection factor of ten times the OEL.