Percent of total bare-metal mains
Percent of pre 1970 mains
Percent of lost or unaccounted for gas
Hazardous Leaks per 1,000 miles of main
The percentage of gas mains made of older cast iron and bare steel. The federal government and independent safety advocates warn these materials are more prone to rust, corrosion and other failures. Cast iron is older and can be 50 to 100 or more years old. National average: 7%
The percentage of gas mains, regardless of material, that the utility said were installed before 1970. The federal government requires utilities to track the age of its gas mains and says older mains need to be more carefully monitored. National average: 39%
Every year, utilities are asked to report the amount of gas that was "lost or unaccounted for" in their distribution system. The government and utilities concede some of this is because of leaks, but say it can also be issues with measurements, instrumentation and other factors. National average: 2.2%
Gas utilities must report each year the number of leaks and hazardous leaks, the latter of which are leaks that posed a threat to people or property. This figure is the number of hazardous leaks from gas mains reported in 2013 per 1,000 miles of pipe. National average: 35 hazardous leaks per 1,000 miles.