Fuel gas safety
By Ron George
President, Ron George Design & Consulting Services
There are several codes and standards that can apply to a given fuel gas installation. Compliance with the applicable codes is mandatory, along with some common sense when dealing with safety for fuel gas systems. Fuel gas systems are covered by the Federal Energy Regulatory Commission and in the International Fuel Gas Code, The Uniform Plumbing Code, the National Fire Protection Association’s NFPA 54 National Fuel Gas Code, the Department of Transportation and state and local laws and ordinances. Fuel gases, like natural gas, propane or butane, can efficiently and inexpensively provide the fuel for common appliances like water heaters, furnaces, clothes dryers, ovens, stoves, fireplaces and other commercial and industrial equipment and appliances.
Fuel gas piping must be installed to be leak free to prevent a dangerous build-up of explosive gases inside a building.
Leak tests on fuel gas piping commonly are done by pressurizing the piping with air prior to filling it with fuel gas and using a spray bottle with a soap and water solution to spray each joint to check for leaks, which will show up as bubbles. Sometimes you will have people fill the system with gas and check for gas leaks with a cigarette lighter or a match. They usually only do that once until they find their first good leak. Once they have experienced a flash fire or explosion they learn quickly not to use an open flame to locate a gas leak. I call this the Darwin testing method or the explosive test method. If they don’t get burned, killed or blow up the building, they learn you should not test for leaks with an open flame. They usually learn to keep a spray bottle with some liquid soap in their toolbox to test for gas leaks by spraying each joint with soapy water.
Odorant added
Because fuel gases are odorless and flammable, there are federal regulations requiring an odorant to be added to fuel gases to help warn of leaks in the piping system; however, the specific type of odorant and amount is left up to the gas providers.
To ensure that gas leaks are more easily detected, natural gas odorization with Mercaptan is mandated for public safety by the Department of Transportation (DOT). The DOT requires natural gas distribution companies to inject a harmless odorant into natural gas to give it an odor. Federal regulations, 49CFR, 192.625, “Odorization of Gas,” requires that gas transmitted interstate be odorized. The odorants most commonly used are mixtures of two general classes of organosulfur compounds — mercaptans and sulfides.
The Code of Federal Regulations has the following text:
Code of Federal Regulations 49 CFR - CHAPTER I
S.192.625 Odorization of gas.
(a) A combustible gas in a distribution line must contain a natural odorant or be odorized so that at a concentration in air of one-fifth of the lower explosive limit, the gas is readily detectable by a person with a normal sense of smell.
The presence of natural gas at 1.26% in air must be detected by smell.
The odorant is strong enough that it can usually be detected by smell at concentrations below the lower explosive or lower flammable limit. Since there is no way to tell if the lower flammable limit has been achieved, you should treat all incidences where gas is detected as a potential for an explosion or fire.
Ethyl mercaptan is a common odorant used for this purpose and has the distinctive smell of rotten eggs. There are other types of odorants or thiols used to give fuel gases a distinctive odor. Ethyl mercaptan is commonly used for this purpose since it is chemically stable when mixed with natural gas or propane, and it has many of the same physical characteristics of propane. One can be reasonably assured: if ethyl mercaptan's distinctive rotten egg odor is detected, fuel gas vapors may also be present.
The odorant was required in fuel gas shortly after a gas explosion in a New London, Texas school. The explosion occurred on March 18, 1937, when a natural gas leak caused an explosion, destroying the New London school. The disaster killed in excess of 295 students and teachers, making it the worst catastrophe to take place in a U.S. school building. Experts from the United States Bureau of Mines, which investigated the incident, concluded that a connection to a gas line was faulty. The connection had allowed gas to leak into the school, and since natural gas was invisible and at that time was odorless, the leak was unnoticed. To reduce the damage of future leaks, and aid in detection, the Texas legislature began mandating within weeks of the explosion that thiols or (mercaptans) be added to natural gas. Federal laws now require fuel gas to be odorized, but there is nothing mandating what the odorant should be. In Las Vegas, the Mirage Casino uses natural gas in large quantities to produce the volcanic eruption in the volcano in front of the casino. The facility engineers did not want to alarm the public because initially when there was a slight wind it was possible to smell the mercaptan or rotten egg smell prior to the eruption. The solution was to provide a scrubber to remove the mercaptan from the fuel gas followed by a resin tank filled with pina colada oil. Now the gas smells like pina colada so guests smell a tropical coconut smell prior to the eruption. The strong odor of many thiols or ethyl mercaptan makes leaks quickly detectable. The practice quickly spread worldwide.
A lawsuit was brought against the school district and the Parade Gasoline Company, but the court ruled that neither could be held responsible because at that time odorants and gas detectors were not required. Natural gas now has an odor similar to rotten eggs, or ethyl mercaptan, so that even the smallest leaks can be detected. If you ever smell gas you should not turn on any lights, use the telephone or do anything that could make a spark. You should open some windows and doors for ventilation and get everyone out of the building immediately and use a telephone away from the building to call the fire department and the gas company. Stay out of the building until you are told it is safe.
Fuel gas odor fade
Fuel gas odor fade is a serious, yet relatively unknown phenomenon. I have been a volunteer firefighter since 1982 and I am a certified fire investigator. I also have investigated several fuel gas and propane explosions and in some cases the occupants have said they did not smell anything. There is a lot of data on the subject of fuel gas odor fade, but it does not seem to be widely known within the plumbing and pipe fitting industries. I would like to see the UA cover fuel gas odor fade in their plumbers and pipe fitters apprentice training programs.
Natural gas or propane with odorant added has that distinctive smell. Natural gas or propane when in its natural state is typically colorless, tasteless and odorless. The natural gas or propane is often delivered through a high pressure transmission pipe to your local gas utility company with or without the odorant added where they meter it, reduce the pressure and distribute it in their local utility distribution system. The gas company also adds an odorant to the gas before distributing the gas.
In new piping installations, all new gas-piping materials are porous and have the ability to absorb the odorant. Black iron pipe is the most likely to cause this phenomenon as the iron oxide and porous walls, if colder than the fuel gas, can condense the odorant and absorb the odorant in the dust, dirt, mud, iron oxide and pores of the pipe wall. Simply stated, the odor is absorbed into the walls of new pipe. The porosity of the pipe, the joining methods used and the temperature variations the fuel gas is piped through are three contributing factors to absorption of the odorant and odor fade. Oxidation or rust in the piping, along with cutting oils, water, dirt or any other foreign substances inside the piping system tend to absorb the odorant until they are saturated. Until the piping system has absorbed enough of the odorant to be saturated and essentially coat the inside walls of the pipe, the absorption process will continue and the odor fade will occur.
All new piping systems absorb the odor. The larger the system, the longer it takes to “pickle” or coat the walls of the pipe with the odorant.
Purging gas lines
The proper procedure for purging a gas line should be to use a hose with a hose clamp of duct tape and route the hose to the outdoors so that flammable gases do not collect inside of a building and create an explosion hazard. It only takes a very small percentage of gas in the volume of the room to reach the lower explosion limit (LEL).
Natural gas can have a heat content or caloric value of 950 to 1,100 British thermal units (Btus) per cubic foot (CF), and normally we calculate natural gas with the caloric value of 1,000 Btus/CF
The specific gravity of natural gas is about 0.60 - .65 (Air =1.00)
Natural gas is lighter than air and it will eventually dissipate when released. The lower flammability limit for natural gas is 3.9 percent gas to air ratio and the upper flammability limit is 15 percent gas to air for the upper flammability limit. Below 3.9 percent gas to air mixture is too lean for combustion and above 15 percent gas to air mixture is too rich for combustion.
This odor fade phenomenon is not a new issue, it has been known and recognized by the gas companies for many years. Most gas companies refer to it in their safety manuals and websites. Most gas companies are aware of the odor fade phenomenon and are required by law to do periodic testing of the odorant levels in the distribution piping and adjust the amount of additive as needed. The odorant must be detectable at a percentage well below the lower flammable limit.
One-call utility location programs
If someone is planning to dig a post hole for a fence, excavate to plant a tree, tear down a building or engage in any other underground earth trenching or moving activity, they should contact a utility one-call program. The one-call programs will typically send out people to locate underground utilities in the area of the proposed excavation. The one-call services are typically funded by the utility companies and they dispatch someone with ultrasound or metal detectors to locate underground utilities. They typically mark the utilities with paint or flags to show a contractor where gas, electric, phone, water and waste lines are located to help avoid construction accidents or problems. Some one-call programs simply contact each utility and they send their own people out to locate the underground utilities. Cutting a buried utility line can be dangerous, costly and inconvenient.
When utility locaters respond to a utility location request, they usually mark where the underground facilities are in the area. If there are no underground facilities buried in the area, the locating personnel sometimes note this as well. This is often done by painting “OK” on the ground and placing a company flag to indicate which utility company has responded to the request. This does not mean it is OK to dig, it may mean that utility checked for their particular utility lines and did not have any underground utility lines in the area of the proposed excavation.
The excavator must then correlate the responses with the list of notified companies to ensure that every company has responded before beginning the project and wait the required 48 hours. When excavating around underground utilities, the standard practice is to hand excavate until the utility line is located and then carefully expose it so the excavation work can continue.
Color coding of piping systems
The American Public Works Association (APWA) has Uniform Color Codes for temporary marking of underground utilities. The color for natural gas, oil, steam, petroleum or gaseous utilities such as propane or butane is yellow. The color codes are listed below:
APWA Uniform Color Codes
Red — Electric Power Lines, Cables, Conduit and Lighting Cables
Yellow — Gas, Oil, Steam, Petroleum or Gaseous Material
Gold — Communication, Alarm or Signal Lines, Cables or Conduit
Blue — Potable Water
Green — Sewers and Drain Lines
White — Proposed Excavation Limits or Route
Pink — Temporary Survey Markings, Unknown/ Unidentified Facilities
Purple — Reclaimed Water, Irrigation and Slurry Lines
Carbon monoxide detectors
Not too long ago there was a code battle to try to get smoke detectors mandated in residences, dormitories, hotels and motels. The idea was to put smoke detectors in areas where people were sleeping to wake them if there was a fire while they were sleeping. Recently, there have been code change proposals to mandate carbon monoxide detectors. Carbon monoxide detectors are not currently mandatory by code, but they are common on most mechanical rooms with fuel burning appliances to monitor for deadly carbon monoxide fumes. I suspect that within the next few years, carbon monoxide detectors will be required in buildings where people are sleeping, because it makes sense. The technology is getting better and they do save lives. As a volunteer firefighter, I have answered many alarms for carbon monoxide detector activations. In many cases, there were problems with the mechanical systems where the occupants were tired and nauseated and flushed, which are all signs of carbon monoxide poisoning. We had our fair share of false alarms from low batteries, as well.
It is wise to have a working smoke detector and carbon monoxide detector on all levels of a residence; establish a home evacuation plan. Stay safe, and don’t use an open flame to look for a gas leak.
Ron George is president of Ron George Design & Consulting Services. He is the former Chairman of the International Residential Plumbing & Mechanical Code Committee and he serves on the International Association of Plumbing & Mechanical Officials (IAPMO) Code interpretation Answers and Analysis Committee and the IAPMO Standards Council. He is active in Plumbing Code and Plumbing Product Standard development and consulting. His company specializes in plumbing, piping, fire protection and HVAC system design. He provides plumbing and mechanical code consulting, plumbing product standard consulting and forensic investigations and litigation support for plumbing and mechanical system failures. E-mail: rgdc@rongeorgedesign.com. Web site: www.rongeorgedesign.com.