Comprehensive and Detailed Explanation:
Group E Diffusers: These non-aspirating diffusers provide laminar, downward airflow. ASHRAE Standard
170 and FGI Guidelines recommend placement in the ceiling center, directly above the surgical table, to ensure clean air blankets the sterile field.
Option Analysis:
A: Correct-center ceiling placement is standard for ORs.
B/C: Sidewall or perimeter placement disrupts laminar flow.
D: Substerile areas are adjacent, not the OR itself.