Sprinkler design density is the rate at which a sprinkler system must deliver water over a defined design area, expressed in gallons per minute per square foot (gpm/sq ft). Together with the design area and duration, it sets how much water the system and its supply must provide.
Under NFPA 13, density depends on the hazard classification of the space. Parking garages were long classified as Ordinary Hazard Group 1, typically about 0.15 gpm/sq ft over 1,500 square feet. The 2022 edition reclassified parking garages to Ordinary Hazard Group 2, about 0.20 gpm/sq ft, reflecting larger vehicles, more plastics and electric vehicles. Mechanical-access and automated garages with stacked vehicles are treated as higher hazards. See mechanical-access parking garage.
In parking facilities
- Which garages are sprinklered. Enclosed parking garages require sprinklers under the IBC; recent editions have extended requirements to some open garages. Check the edition adopted locally.
- Freezing. Open garages in cold climates usually need dry-pipe or antifreeze systems.
- EV fires. Battery fires burn long and can reignite. Water remains the main suppression tool, and the debate is about density, duration and fire department access rather than exotic agents. See thermal runaway.
- Existing garages. A garage designed under an older edition is not automatically required to upgrade, but owners adding EV charging should review fire protection with the fire marshal.
The Parkonomics view
The answer to the modern car fire is still water, delivered by design. When adding chargers or converting a garage, ask the fire protection engineer what edition the system was designed to and whether its density and supply still fit the vehicles parked there.
Related terms: NFPA, Thermal Runaway, International Fire Code, Enclosed Parking Garage, Mechanical-Access Parking Garage