Author(s): Angelo Verzoni. Published on November 1, 2020.

Early Warning

As gas leaks become more frequent, the risk of deadly explosions increases. A new NFPA standard—NFPA 715, Standard for the Installation of Fuel Gases Detection and Warning Equipment—aims to address the problem.


Listen to an NFPA Podcast about gas explosions and NFPA 715.

On August 10, the morning quiet in Baltimore’s Reisterstown Station neighborhood was shattered by an immense explosion. Three rowhouses were leveled by the blast, and dazed residents stumbled through the rubble in search of loved ones. “This is a horrendous situation,” Niles Ford, chief of the Baltimore City Fire Department, told the Baltimore Sun, as responding firefighters combed the site for survivors. The incident left two dead and dozens more injured. Investigators determined the explosion was caused by a gas leak, but that it did not involve pipes or equipment belonging to the utility, Baltimore Gas & Electric.  

The Baltimore incident joined a growing list of deadly gas explosions that have made headlines in recent years. In September 2018, the Merrimack Valley region of Massachusetts was rocked by a series of natural gas explosions and fires that killed one person and left more than two dozen injured. Almost exactly a year later, a firefighter was killed and several other people were injured when a propane gas explosion leveled a building in Farmington, Maine. Similar incidents are occurring around the world as well; a month after the Baltimore blast, an explosion linked to a gas leak in a mosque in Bangladesh killed two dozen people.

RELATED: Read “Big Assist,” the July/August 2019 NFPA Journal cover story on the 2018 Merrimack Valley gas explosions 

Research has shown the incidents that make it into headlines are just the tip of the iceberg. An NFPA report released in late 2018 found that, on average, natural gas ignites 4,200 home fires each year in the United States alone. According to the report, US fire departments respond to an average of 125,000 residential natural gas or liquefied petroleum gas leaks annually, an increase of about 25 percent compared to 2007. Gas safety experts say detecting leaks before they result in catastrophe is one of the best ways to combat the problem. 

To reduce the threat, a new standard is being developed by NFPA that will establish requirements for the installation of equipment that can detect and warn occupants of a gas leak. Set for release in 2022, NFPA 715, Standard for the Installation of Fuel Gases Detection and Warning Equipment, will apply to equipment manufactured to detect leaks of fuel gas, which includes natural gas and liquefied petroleum gases like propane and butane. 

According to experts, NFPA 715 will fill a safety void that grows with each large-scale incident. “When you look back and see the losses, there appears to be a hole in fire safety that needs to be addressed,” said Stephen Olenick, chair of the NFPA 715 technical committee. “This is a standard that’s going to give municipalities and building codes something to point to that shows how to do this right. We’re hopeful it’s going to save lives.”

Gas leaks on the rise     

Deadly gas explosions aren’t a new problem. A massive natural gas explosion destroyed a school in New London, Texas, in 1937, killing nearly 300 children and teachers. The Quarterly, the NFPA magazine at the time, observed that “there is evidence of a most terrific force in the great extent of devastation and loss of life that came almost instantly; testimony of bodies tossed 75 feet into the air; an automobile 200 feet distant crushed like an eggshell under a two-ton slab of concrete.” According to NFPA data, the event is the 15th-deadliest fire or explosion in US history.

While no data exists to support an increase in gas explosions or fires over the years, the data does show a sharp increase in leaks in the past 10 to 20 years. From 2007 to 2016, the annual number of US fire department responses to residential gas leaks jumped by over 40,000, from about 100,000 to 141,000, the 2018 NFPA report said. 

A leading theory as to why that’s the case is the fact that America’s gas pipeline infrastructure is aging. In the days following the Merrimack Valley explosions, for example, USA Today reported that one out of every four miles of gas mains in Massachusetts had been installed prior to 1940. When a gas explosion shredded a block of buildings in the East Harlem section of New York City in 2014, killing eight and injuring nearly 50 more, it was later discovered that the leaking pipe had been installed in the 1800s. Last year, the Conservation Law Foundation, an environmental advocacy group based in New England, called the country’s aging gas infrastructure “expensive, leaky, and dangerous.” And less than a year before the deadly Baltimore explosion, the Baltimore Sun ran an article ominously warning readers that the city’s “natural gas system is increasingly leaky.” 

The cause of gas leaks can usually be traced to one of three things: the gas utility’s equipment, equipment on private property, or gas appliances. In the Merrimack Valley incident, the leaks were traced to the gas distribution system of the utility, Columbia Gas. According to the National Transportation Safety Board, highly pressurized natural gas was accidentally released into a distribution system designed for low-pressure gas. The over-pressurized gas raced into homes and other structures, overwhelming household systems and flooding spaces with natural gas vapors. 

Over 100 buildings were destroyed during the September 2018 gas explosions and fires in the Merrimack Valley region of Massachusetts. (Getty Images) 

When an event like this occurs, it doesn’t take much gas to create the conditions capable of producing fires or explosions. The concentration of propane vapors in the air needed to spark a fire—known as the lower flammability limit (LFL)—is only about 2 percent. For natural gas, it’s closer to 5 percent. When the LFL is reached, an ignition source can come from something as seemingly innocuous as flipping the switch to turn on an appliance. That’s why emergency officials in the Merrimack Valley region quickly ordered the shutoff of electricity once explosions and fires began to occur. Despite those efforts, more than 130 buildings in three communities were damaged by fires or explosions, including five that were completely destroyed. 

Detection is key   

With efforts to replace aging gas pipeline infrastructure costly and time-consuming, bolstering gas detection measures has become the next most logical step to improve safety. 

For the vast majority of the general public, the only gas detector they have now are their noses. Gases like natural gas and propane are laced with mercaptan, a harmless, distinct-smelling chemical, so you know when there’s a leak. But “odor fades and not everyone can detect odor readily,” Alexander Ing, an engineer in the Hazardous Materials division at NFPA, wrote in a blog posted the day after the Baltimore incident. Studies show that human smell succumbs to a phenomenon known as olfactory fatigue after a minute or two of being exposed to the same odor, meaning you can no longer smell it. 

Plus, if a leak occurs underground, the earth can essentially extract the mercaptan out of the gas. This happened in the Maine incident, after an underground propane gas line was punctured by a company performing construction work at the property. A few days later, a maintenance worker reported the smell of gas to authorities, but when firefighters arrived, no smell could be detected in certain parts of the building. “When they used gas detection meters, though, they were picking up high readings,” said Maine State Fire Marshal Joe Thomas. “So that mercaptan was actually scrubbed out of the gas by the earth it was moving through.”

About a month after the explosion, Lois Reckitt, a Maine state representative, proposed a bill to require gas detectors in certain properties in the state. “There are no regulations, and I just thought that’s crazy, especially with what just happened in Farmington,” she told local news reporters at the time. The bill is still being considered by state lawmakers, who have been in recess due to the COVID-19 pandemic.  

The September 2019 propane explosion in Farmington, Maine, left debris scattered for blocks. (Getty Images)

Currently, anyone can go out and buy a gas detector—and there is a UL standard for their performance—but there’s no comprehensive guidance on installing them, said Olenick, the NFPA 715 technical committee chair who works as an engineer at Maryland-based Combustion Science & Engineering. “You could perhaps look at the manufacturer instructions, but there’s really no prescriptive requirements,” he said. “That was where the push for the standard came from, and it’s our hope that the standard will provide guidance to these municipalities and to the Life Safety Code® and to model building codes. They will have a standard that will tell them how to properly install these devices.”  

The road to standardization officially began in August 2018, when the American Gas Association sent a request to NFPA for a document like NFPA 715 to be developed. The technical committee will meet virtually until the coronavirus pandemic eases, Olenick said, and the standard is slated for release in June 2022. 

Before the NFPA 715 technical committee could get started on writing the standard, though, they needed research showing how gases like natural gas and propane disperse and where detectors should ideally be installed based on that dispersion. That’s where the Fire Protection Research Foundation stepped in. 

The foundation’s work culminated in August with the release of a study titled “Combustible Gas Dispersion in Residential Occupancies and Detector Location Analysis,” the findings of which will heavily inform the new standard. The study found that, in general, detectors aren’t as effective when placed near HVAC equipment, door gaps, stairwells, or other areas where there are openings or airflow. For natural gas, detectors worked best when placed closer to the ceiling, while for propane, they worked best when placed closer to the floor—this made sense to researchers, as natural gas vapors are lighter than air and propane vapors are heavier. 

RELATEDRead an October 2018 NFPA Research report on natural gas and propane explosions, fires, and leaksread the Fire Protection Research Foundation’s August 2020 report on gas detector location analysis

Scott Davis, one of the authors of the study and CEO of the Maryland-based fire and explosion safety consultant agency Gexcon US, said the report represents “a very good first step” in the standardization process. 

“We looked at numerous leak conditions and leak rates for numerous structural configurations to create what I would call a performance-based study,” he said. “And we’re doing this before we actually start putting these detectors up. So this is a huge piece of work toward getting the optimal detector location such that you detect the condition prior to the hazard.” 

Thomas said a standard like NFPA 715 could have made a difference in the Maine incident. “If that building had included detectors that were compliant with what 715 is going to detail, you would’ve had a detector reacting to the [concentration] of the gas and not the mercaptan,” he said. “In circumstances where humans aren’t able to detect the gas, those detectors could have provided an earlier warning.” 

In other situations, like the 2018 Merrimack Valley incident, it’s less clear how much impact detectors might have had. “It was such a rapid over-pressurization, I don’t think detectors would’ve made a difference for some of those properties,” said Brian Moriarty, fire chief in Lawrence, Massachusetts, one of the cities hit by gas-related fires and explosions. “In other properties, though, where we didn’t necessarily have a fire or explosion but the home still filled with gas, detectors could’ve been a great enhancement to life safety.”

A parting piece of advice Moriarty shared was to not overlook human behavior and the need for public education when writing the new standard. “We see with smoke alarms that people don’t necessarily evacuate when alarms sound, that they’ll take out the batteries,” he said. “I think you have to have an audible instruction that says get out of the house, don’t use any appliances or devices, and call 911 from outside the building.” 

Olenick agreed that public education will be key to the long-term success of NFPA 715. “We’re going to need to do more than just say, ‘Put this alarm in and do it this way,’” he said. “Firefighters and safety professionals will have to say, ‘Hey, when it does sound, these are the steps you should take.’ It’s a team effort.”

ANGELO VERZONI is staff writer at NFPA Journal. Top photograph: Getty Images