Oh, that funky smell of gas. We are all familiar with it. One whiff immediately sends off those warning signals in your mind, “Danger Will Robinson, danger!”
Why is that? Because from a young age we are conditioned by our parents that gas is dangerous and the smell warns you of the danger. But, it hasn’t always been that way.
Natural gas is a fossil fuel, mostly methane, created by the decomposition of plants and animals buried deep in the earth where it is exposed to intense heat and pressure for thousands of years. It is a nonrenewable resource because we are using it faster than nature can replenish it. At our present consumption rate, the known gas reserves would last about 250 years. Factor in increases of consumption and those same resources could be depleted in as little as 80 to 100 years.
Because the gas is processed to rid it of impurities, natural gas in colorless and odorless when it is refined. Back in 1937 at the New London School in Texas, on March 18, at 3:17pm, there were 500 students in the school from grades five through 11 and 40 teachers. Lemmie Butler, the Shop Instructor, turned on a sanding machine. A spark from the machine ignited gas that had leaked undetected into a crawl space 253 feet long and 56 feet wide below the shop. The explosion that ensued was heard 12 miles away as it seemed to lift the building off the ground and drop it. It leveled the roof, collapsed walls and sent a piece of concrete 2-tons in weight about 200 feet in the air before it crushed a 1936 Chevrolet.
In total, 294 were killed, 116 were seriously injured, and only 130 escaped serious injury. Fortunately, the younger grades K-4 had already been sent home for the day. It was the worst disaster this country had seen at the time, yet, few people know about it. A cenotaph monument now stands where the school once stood to memorialize the victims and a museum was constructed across the street.
It was as a result of this explosion that the gas purveyors realized they had to put an odorant into the gas to alert people of a leak. The compound typically used is called mercaptan. Only a minute amount is required to odorize the gas. In recent years, it has been found that odorants are sometimes masked by other naturally occurring elements in the gas such that it cannot be detected by the nose but can be detected by measuring instruments. This phenomenon is not yet understood and the gas industry is doing research into why this odor masking sometimes occurs. Here at Murray Company we frequently inject our own odorant when filling a large gas system to avoid the potential of odor masking and associated accidents.
When natural gas is refined, propane, butane, and ethane are natural byproducts of the process. Interestingly, natural gas is not easily liquefied. It requires either a cryogenic process (LNG) at a temperature of -260°F, or a compression process (CNG) at a pressure of 3,000 psi. Where gas pipelines do not exist, natural gas is generally transported in cryogenic trucks.
In contrast, the byproducts of natural gas are much more easily liquefied. Propane (LPG) liquefies at 320 psi while butane (LBG) liquefies at just 32 psi. This is why plastic cigarette lighters are fueled with butane, while propane – the more abundant byproduct – is stored in metal containers that withstand the required pressure quite easily. Ethane is not generally used for commercial purposes. Propane and butane also have odorants added. Propane is odorized with ethanethol, which is why its small is distinct from natural gas, while butane is odorized with a combination of hydrogen sulfide and mercaptans, giving it a smell more similar to natural gas.
Getting back to natural gas, there was an accident here in Los Angeles not unlike that of the New London School, but different in nature and smaller in scale.
Late in the afternoon of March 24, 1985, methane gas ignited below the floor of a Ross Dress-for-Less clothing store on 3rd Street in Los Angeles. The ignition of the gas occurred in an auxiliary room of the store, possibly a smoking room. The explosion blew out the windows and collapsed the roof injuring 23 people quite seriously as flames burned through the night from the floor of the store.
Forty-two feet below the store, it was later determined, lay a pressurized pocket of methane that is known to occur naturally in many parts of the greater Los Angeles area. Famous for the La Brea Tar Pits, graveyard of the saber-toothed tigers, the area had plenty of plant, animal, and hydrocarbon remains from many thousand years ago. The combination served as a perfect breeding ground for methane production.
In the wake of this disaster, and since many areas of Los Angeles are known to have the potential for similar methane conditions, whenever methane is detected on a construction site by the geotechnical engineer, a methane venting system must be installed. The system usually consists of a series of perforated pipes below grade that are collected in multiple locations and vented through the roof of the building. The vents are basically the same as the sanitary vents – cast iron pipe with no-hub couplings. The requirement spawned a new industry – that of methane gas consulting. The methane gas consultant lays out the system that is generally installed by the plumbing contractor.
Meanwhile, unrelated to gas but of general interest, some of you probably heard that on December 8, 2014, Los Angeles had its largest fire ever when a wood-framed apartment structure went up in flames while under construction. The building was huge – 900 feet 200 feet, and a total floor area of 1.3 million square feet. Two-hundred and fifty fire fighters responded, but they essentially decided just to let it burn itself out, which it did in under two hours. It was so hot it melted highway signs on the adjacent 101 freeway. It also melted windows and set off sprinkler heads in the building across the street, which ironically housed the Los Angeles Department of Building and Safety. Arson is suspected. n
Timothy Allinson is vice president of Engineering at Murray Co., Mechanical Contractors, in Long Beach, Calif. He holds a BSME from Tufts University and an MBA from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a LEED accredited professional. Allinson is a past-president of ASPE, both the New York and Orange County chapters. He can be reached at firstname.lastname@example.org.