How many air exchanges does the buffer area need to have?

The correct answer is A. 10 air exchanges. According to USP <800> standards, the buffer area in a pharmacy handling hazardous drugs must have a minimum of 10 air exchanges per hour to ensure proper ventilation and decrease the risk of occupational exposure to hazardous drugs. This requirement helps in maintaining a safe environment for pharmacy staff who handle these drugs.

Options B, C, and D are incorrect because they do not align with the specific requirement of 10 air exchanges per hour as mandated by USP <800> guidelines for the buffer area in pharmacies handling hazardous drugs.