Nitrogen dioxide (NO2) is a reddish-brown, toxic gas formed when fuel burns at high temperature. In parking facilities, its main source is vehicle exhaust, particularly from diesel engines.
Short-term exposure irritates the lungs and airways. Because diesel engines emit relatively little carbon monoxide but significant nitrogen oxides, a ventilation system controlled only by CO sensors can miss a diesel-heavy garage. For that reason the International Mechanical Code requires demand-controlled ventilation in enclosed garages to use both carbon monoxide and nitrogen dioxide detection.
In parking facilities
- Detection. NO2 sensors work alongside CO sensors to start and modulate exhaust fans. See demand-controlled ventilation.
- Where it matters most. Enclosed and below-grade garages, loading docks, bus and truck parking, and areas where vehicles idle.
- Maintenance. Gas sensors drift and must be calibrated or replaced on the manufacturer’s schedule.
- Electrification. As the fleet electrifies, exhaust gases decline, but sensors remain required until codes change.
The Parkonomics view
Ventilation fans are among the largest energy loads in an enclosed garage. Sensors that work let the fans rest most of the day; sensors that drift either waste energy or fail to protect people. Calibrate them like the life-safety devices they are.
Related terms: Carbon Monoxide, Demand-Controlled Ventilation, Mechanical Ventilation System, Enclosed Parking Garage, International Mechanical Code