Gas Leaks

Written on: February 24, 2015 by ICM

By Daniel Sheridan
Battalion Chief, FDNY
Just last month, in my own community, we dodged a potentially huge catastrophe.
One of my neighbors’ houses developed a gas leak at the meter, which resulted in a fire that burned a good portion of the house. It could have been much worse had the gas accumulated in the basement and found an ignition source.
The following week, the house next door developed a leak inside a brand new stove that had just been installed. The people living there called the local utility and when they didn’t show up in a reasonable amount of time, went to bed. The utility worker showed up at 2:00 am. The gas levels in the house were elevated (4%) and didn’t rise any higher once the gas was finally shut down at the stove.
Gas is extremely safe and a great, clean source of energy, when it stays in its pipes. The problem exists when it gets out of its cage and finds an ignition source. It still remains a volatile substance. Natural gas is lighter than air. Depending upon the exact composition, it has a vapor density of 0.59 to 0.72, a lower explosive limit (LEL) of 3.9–4.5%, and an upper explosive limit (UEL) of 14.5–15%. Its ignition temperature is 900°F to 1,170°F.
This means that if you have a leak in an appliance and the gas fills the space to these explosive levels, the results are catastrophic. The same holds true with propane. Propane gas is heavier than air. It has a vapor density of approximately 1.5 to 2.0, LEL of 2.15% and UEL of 9.6%. Its ignition temperature is 920°F to 1,120°F.
When the propane or the natural gas comes in contact with any type of ignition source, you will have a devastating explosion. The ignition source can be anything from a pilot light to a static charge.
There is an enormous amount of piping in the U.S. that has been in the ground, walls and under the streets for years, exposed to all sorts of debilitating corrosives and weather differences. As the weather get colder, it becomes more difficult for gases to migrate upward through the frozen or snow- and ice-covered ground and into the atmosphere to dissipate.
To cite an example, USA Today on Jan. 16, 2014 was quoted as saying,  “As the use of natural gas booms in the United States, scientists are testing for pipeline leaks. They found more than 5,800 leaks under the streets of Washington, D.C., some potentially explosive.”
Refer to National Fire Prevention Agency (NFPA) 921, section It is common for fuel gases that have leaked from underground piping systems to migrate underground (sometimes for great distances), enter structures, and create flammable atmospheres. Both lighter-than-air and heavier-than-air fuel gases can migrate through soil; follow the exterior of underground lines; and seep into sewer lines, underground electrical or telephone conduits, drain tiles, or even directly through basement and foundation walls, none of which are as gastight as water or gas lines. Such gases also tend to migrate upward, permeating the soil and dissipating harmlessly into the atmosphere. Whether the path of migration is lateral or upward is largely a matter of which path provides the least resistance to the travel of the fugitive gas, the depth at which the leak exists, the depth of any lateral buried lines that the gas might follow, and the nature of the surface of the ground. If the surface of the ground is obstructed by rain, snow, frozen earth or paving, the gases may be forced to travel laterally. It is not uncommon for a long-existing leak to have been dissipating harmlessly into the air until the surface of the ground changes, such as by the installation of new paving or by heavy rains or freezing, and then be forced to migrate laterally and enter a structure, fueling a fire or explosion.
In my job as a Battalion Chief with the New York City Fire Department (FDNY), I have responded numerous times to help our local utility company gain entry into basements of houses that are affected by a gas leak in the street. Many of those times, we have found houses closest to the leak with levels as high as 2%. The problem usually is greatest in the sleeping hours. Danger arises when the gas accumulates in basements and people are unaware of the situation. Another possibility that may exist is if the odorant (Mercaptin) gets washed out, leading to an odorless and colorless gas entering our residences.
Refer again to NFPA 921, section
A)    Loss of Odorant Due to Gas Migration in Soil
Gas odorants can be removed by dry, clay-type soils, and not by sand, loams or heavily organic soils. Certain odorant components are better than others in terms of their ability to resist adsorption by clay-type soils. A large leak gives a lower contact time with the clay-type soil, and results in lower losses due to adsorption.
B)     Loss of Odorant Due to Adsorption of Odorant on Pipe Walls
All odorant components are adsorbed by pipe walls to some extent. This is particularly true of new pipe (steel or plastic). Many natural gas companies treat the gas in new sections to a heavier dose of odorant after the section is placed in service. Gas odorants can be adsorbed in gas pipe that has been in continuous service, if the flow rates of gas are lower than normal. This is a typical condition in many gas companies in the transition between winter and summer usage levels. A decrease in pressure in the system, which increases gas flow rates, easily remedies this problem. Any portion of a gas system that is subject to low flow rates is subject to increased loss of odorant due to adsorption.
The Flowtech Safety System has a solution. Our system will detect a gas leak and will shut down the gas at the source before it has a chance to reach the Lower Explosive Limit. Flowtech Safety System detects a gas leak (LPG or Natural) and alerts you of a dangerous gas leak or a buildup of gas within your home. The Flowtech Safety System also has an additional safety factor, which sends a signal wirelessly to a shutoff valve installed near the gas meter. The gas systems adhere to the European System 50294.
Daniel Sheridan is a Battalion Chief with 28 years of experience with the New York City Fire Department (FDNY). In 2014, he became President and CEO of Flowtech Safety Systems, introducing the product to the U.S. market.