most other flammable/energy gases have vapor densi-ties > 1 and tend to move downward.
Natural gas is nontoxic and considered a simple
asphyxiant. Utility companies indicate that the
natural gas mixture from the pipeline will typically
have a lower explosive/flammable limit (LEL/LFL) of
five percent and an upper explosive/flammable limit
(UEL/UFL) of 15 percent. Five to 15 percent natural
gas in air is considered the “flammable range.”
Natural gas typically originates in underground
deposits and is extracted in a number of ways. Energy
companies have also developed alternative processing
methods to create natural gas and, currently, there is
a “boom” in natural gas in North America, which has
reduced gas prices and encouraged expanding use of
natural gas. Transmission pipelines transport the natural
gas at high pressures [up to 999 pounds per square inch
throughout the country to local natural gas utilities.
These companies purchase the gas and distribute it to
the customer through a distribution piping system.
Gas distribution systems operate at pressures ranging from ¼ psi to 99 psi and consist of mains, services, valves, and meters. In a gas distribution system,
services and mains are constructed of steel, cast iron,
ductile iron, wrought iron, or plastic, depending on
the system age and type of service.
Natural gas transmission and distribution piping
system installations must conform to rigid con-
struction requirements set forth in ANSI B31.8,
Gas Transmission and Distribution Piping System
Standard. National Fire Protection Association 54,
installation of natural gas piping and appliances inside
buildings. The federal Department of Transporta-
tion (DOT) maintains jurisdiction over the safety of
transmission pipelines. Distribution systems must
also comply with DOT regulations as well as Public
Utility Commission requirements.
Utility companies must ensure the integrity of their
natural gas distribution systems through a comprehensive safety program that involves surveying,
monitoring, maintenance, and testing. Most utility
companies have responsibility for the distribution system up to and including the natural gas meter. Property owners are responsible for all natural gas piping
inside buildings downstream of the meter. Many rural
and suburban areas have no piped natural gas service.
In these areas, the gas service may be bottled gas,
such as liquid propane gas (LPG). The information
contained in this article does not apply to LPG. Fire
departments should be aware of where there is natural
gas service in their coverage areas.
Here is guidance for handling incidents involving
On scene. Immediately notify the utility company
once you’ve determined an incident involves natural
gas. Once they arrive on the scene, instruct utility company personnel to report to the incident commander
(IC) or the liaison officer in a well-developed incident
command system (ICS). Many utility workers receive
ICS training to work within the system and can assist
in evaluating the problem, recommend actions to take,
and request additional resources as needed.
The San Bruno pipeline explosion occurred on September 9, 2010, in San Bruno, California, a suburb of San Francisco, when a natural gas pipeline owned by Pacific Gas
& Electric exploded into flames in the Crestmoor residential neighborhood two miles west of San Francisco International Airport. (Photo by MisterOh.)