GLOSSARY

Carbon Monoxide (CO)

Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion. In parking garages it comes mostly from cold starts and idling gasoline engines, and it is the main pollutant that enclosed-garage ventilation is designed to control.

CO LEVELS THAT MATTER IN A GARAGE (PARTS PER MILLION, LOG SCALE)11010010009 ppmEPA outdoor35 ppmNIOSH limit50 ppmOSHA limit200 ppmNIOSH ceiling1200 ppmIDLHSensors run the fans to keep CO well below workplace limits. Setpoints come from the engineer and code.
Garage ventilation exists to keep carbon monoxide far below the levels that harm people. Reference points: EPA ambient standard, NIOSH and OSHA workplace limits, NIOSH ceiling and the level immediately dangerous to life or health.

Open garages ventilate naturally. Enclosed and below-grade garages need a mechanical ventilation system, sized under the International Mechanical Code at 0.75 cfm per square foot of floor area unless an approved gas detection system controls the fans.

Exposure benchmarks

  • EPA outdoor standard: 9 ppm over 8 hours.
  • NIOSH recommended limit: 35 ppm over 8 hours; 200 ppm ceiling.
  • OSHA permissible limit: 50 ppm over 8 hours.
  • Immediately dangerous to life or health: 1,200 ppm.

Sensing and savings

  • Gas detection. CO sensors, plus nitrogen dioxide sensors where diesel vehicles park, let fans run at a low base rate and ramp up when readings rise. See demand-controlled ventilation.
  • Drives. Variable frequency drives let fans slow down, and fan power falls roughly with the cube of speed.
  • Calibration. Sensors drift and expire; a dead sensor can leave fans idling or running flat out.
  • Electric vehicles. EVs emit no CO, but codes still require ventilation sized for mixed fleets, and booths, cashiers and attendants still breathe the air.

The Parkonomics view

Garage ventilation is a health system that happens to be one of the biggest energy loads in the building. Sensors and drives let it be both safe and cheap, as long as someone calibrates the sensors.

Related terms: Mechanical Ventilation System, Demand-Controlled Ventilation, Variable Frequency Drive, Nitrogen Dioxide, Enclosed Parking Garage, International Mechanical Code, Volatile Organic Compounds (VOCs), Internal Combustion Engine (ICE)