IMC 404: Enclosed Parking Garages — CO + NO₂ Detection, Full-On vs. Standby Modes

🧠 Plain English: 404.1 — Garage ventilation must run continuously OR automatically via CO + NO₂ detectors listed to UL 2075 installed per MI. Automatic systems: Full-On ≥0.75 cfm/ft²; Standby ≥0.05 cfm/ft² of floor area served. 404.2 — Accessory offices/booths/waiting rooms connecting to a public garage must be positive pressure to the garage and ventilated per 403.3.1.

🧮 Step-by-Step: Full-On cfm = 0.75 × ft². Standby cfm = 0.05 × ft². Controls: CO/NO₂ thresholds for Standby ↔ Full-On; fail-safe to Full-On on detector/BAS fault. Accessory rooms: supply > exhaust to maintain positive pressure.

🏗️ Why It Matters: Common redlines — NO₂ detectors missing (CO only shown), UL 2075 not cited or mounting ignores IOM, Standby 0.05 cfm/ft² not proven, 'positive pressure' noted but no supply-exhaust math.

🔧 Field Tip: Place CO in expected accumulation zones; NO₂ near diesel paths; follow each detector's IOM (heights differ). Trend ppm, fan speed, cfm. Show BAS graphic proving mode switching and fault fail-safe.