Comprehensive and Detailed Explanation:
Airflow Analysis: Supply = 300 cfm, Return = 150 cfm, Toilet Exhaust = 25 cfm. Total exhaust = 150 + 25 =
175 cfm. Net airflow = 300 - 175 = +125 cfm (positive pressure).
AIIR Requirements: ASHRAE Standard 170, Section 7.2.1, mandates negative pressure for Airborne Infection Isolation Rooms (AIIRs), meaning exhaust must exceed supply. Here, the room is positive (+125 cfm), triggering the pressure sensor alarm.
Problem Identification: The toilet exhaust (25 cfm) is insufficient to offset the supply, failing to achieve negative pressure. AIIRs typically require 50-75 cfm exhaust per toilet (Table 7.1), so 25 cfm is inadequate.
Option Analysis:
A: Correct-insufficient exhaust explains the positive pressure in an AIIR.
B: An open door would reduce pressure differential but not explain the airflow imbalance.
C/D: Protective Environment (PE) rooms require positive pressure, which aligns with the +125 cfm, but the alarm suggests an AIIR (negative pressure) context.