NFPA Journal

Just past 8:30 in the morning on July 17, 2007, a tanker-truck filled with a volatile solvent arrived at the Barton Solvents facility, a chemical distribution company and tank farm in the sleepy town of Valley Center, Kansas, just north of Wichita.

The driver parked his rig next to a cluster of 40 steel storage tanks, and a Barton supervisor arrived to do a safety check before unloading the cargo of VM&P naphtha (varnish maker and painters solvent), a highly flammable liquid substance commonly used to make adhesives, resins, inks, and other products. Since flammable liquids traveling through a hose or sloshing in a tank can become charged with static electricity, the supervisor clamped a conductive cable between the truck and an electrical ground station, a common technique known as bonding and grounding. By bonding the truck with the facility’s tanks and other equipment, any static charges could be given a free pathway to dissipate harmlessly into the earth. At least that was the idea.

Instead, as the last of the solvent was being drained from the truck, a single static spark—likely many times less powerful than the shock you feel from touching a doorknob—flickered to life inside the 15,000-gallon storage tank and ignited the naphtha vapors. A sudden violent blast lifted the steel container into the air like a rocket, hurling it 130 feet away, according to a report on the incident by the US Chemical Safety Board. Two adjacent tanks ruptured in the explosion, spilling thousands of gallons of flammable liquid and igniting an inferno that spread in a chain reaction to other tanks, causing them to over-pressurize and ignite. Steel tank tops 10 to 12 feet in diameter, as well as valves, pipes, and other steel parts, were launched into the air with explosive force and rained down on the nearby community. One of the heavy steel lids struck a mobile home 300 feet away, and a pressure valve hit a neighboring business 400 feet away, the CSB report found. About 6,000 residents in Valley Center had to be evacuated from the toxic black cloud wafting from the disaster. No deaths were reported, but 12 people, including a firefighter, required medical attention.


Static electricity inside a storage container was blamed for an explosion and fire at a chemical distribution facility in Kansas.  GETTY IMAGES

While incidents like Barton make it clear that static electricity is not to be taken lightly, its destructive potential seems to escape broad public attention. Even in the safety world, static is rarely given top billing as a hazard of major concern. Until recently, no one had a sense of how often static ignitions like Barton occur, or what the main causes of these incidents are. NFPA’s guidance on the topic, NFPA 77, Recommended Practice on Static Electricity, which was first published in the 1940s, remains one of the organization’s most under-the-radar documents, a fact even its committee members freely admit.

But efforts are underway to change all of that. Early last year, the NFPA 77 technical committee asked the Fire Protection Research Foundation to help it better understand how effective the guide has been at preventing static incidents and what, if anything, should change in upcoming editions. The Foundation enlisted researchers from the United Kingdom to scour international news reports, academic journals, insurance claims, and other sources to create a tally of recent static incidents from around the world and what caused them. The work uncovered nearly 90 incidents since 2001 where static caused an ignition or an explosion, a number that surprised many of the project’s technical panel members.

“To be honest, early in the process our project technical panel was concerned that we wouldn’t be able to find enough incidents to have meaningful statistics for the study,” said Kelly Robinson, a static safety consultant and the chair of the NFPA 77 technical committee. “Pretty quickly we realized that that wasn’t going to be the case.”

As with the Barton explosion, several of the static incidents found in the report involved fires or explosions during the transfer of flammable liquids—but that’s hardly the extent of it. Static has also triggered dust explosions in grain silos and factories, as well as fires in manufacturing plants and in facilities that coat products with paint or solvent. Static is thought to have sparked gas line explosions that have flattened buildings, notably a 2019 blast in Farmington, Maine, that killed one firefighter and injured six others, as well as the building’s maintenance supervisor. Static has even been blamed for explosions that have killed and badly injured people as they’ve pumped fuel at gas stations. In addition, static seems to have a penchant for the dramatic and strange: it is believed to have caused a hospital fire in Oregon in 2013, when static electricity ignited hand sanitizer. In China, static buildup in bundles of cotton yarn ignited a massive fire when a porter carrying the bundles stepped onto the metal floor of a lorry truck, triggering a spark.

Based on the report’s findings, researchers and experts like Robinson now believe that the actual number of static incidents is likely far greater than anyone realized. “I think for every incident that was quoted in that report, there’s probably between 10 and 50 more that happened that are not reported,” said Robinson, who also served as a technical panel member for the project. Many of these unreported events, he said, likely include minor incidents that caused a fright but no injuries and little damage, or that occurred in places with little media coverage that made them difficult for researchers to find. This notion is backed up by the fact that over 60 percent of the static incidents in the report happened in the United States, implying that incidents in other countries are significantly underrepresented, the report’s authors noted.

Just as alarming, the nature of the static incidents uncovered in the report seem to suggest that the guidance in NFPA 77 is either not well known or not closely followed. “Many of the cases analyzed occurred not because of lack of guidance in NFPA 77, but rather a lack of awareness of the guidance, or inappropriate application of the guidance,” the report authors wrote.

As for why that is, Robinson speculates that there are two likely possibilities. “Either NFPA 77 is written in a way that makes it difficult to understand and we need to clarify it, or there are too many people out there that don’t know that NFPA has a recommended practice on static electricity,” he said. “Those are clearly things that we need to address.”

Invisible danger 

Because its processes are largely invisible to us, it can seem that static has a dangerous habit for suddenly appearing at the most inopportune times. But a better and more accurate explanation is that static is an omnipresent part of our world; it’s only when conditions align, when flammable vapors or dust mix at just the right concentration, that we notice how opportunistic and dangerous static can be.

History’s most famous example of the hazardous potential of static occurred in New Jersey on May 6, 1937, when the Hindenburg, an 800-foot-long German airship, ignited and burned in dramatic fashion as it attempted to dock with its mooring mast, killing 35 people. Scientists now believe that a combination of a passing thunderstorm, a light rain, and the ship’s landing ropes dragging on the ground caused the airship’s massive aluminum frame and canvas shell to take on a static charge. The airship’s lift was provided by highly flammable hydrogen, and when a spark found a small hydrogen leak near the ship’s tail, the enormous craft ignited in seconds and fell out of the sky in a roiling inferno.

The Barton incident illustrates how difficult it can be to completely remove static electricity from an environment, even when its potential to cause catastrophic harm is well understood. During its investigation, the CSB learned that a combination of air bubbles, the tank’s fuel level, existing sediment in the filling tank, and the error of pumping the naphtha at too high a velocity all contributed to static building up in the tank faster than it could be dissipated through the ground. The spark occurred because a tiny floating bobber inside the tank—used to gauge its liquid levels—had a loose connection with the gauge tape that it hung from. Turbulence and bubbles from filling the tank caused slack in the tape and made the float rock and sway and occasionally lose connection with the tape entirely. In those brief moments of separation, the float was no longer grounded, allowing for the static building in the tank to discharge and ignite the vapors inside. When it comes to static, small details are enormously important.

“A spark that could ignite the Hindenburg would be between 10 and 100 times too small for a human to even feel, so we’re talking about sparks that you and I would never know happened—but they’re enough to cause an industrial disaster,” Robinson said. “That’s one of our challenges. We’re trying to prevent things that most people don’t even realize happen unless there’s an ignition.”

One reason static can be so hard to eliminate is because it is a fundamental part of how the world works. When two different materials touch—such as your socks to a carpet, or a flammable liquid flowing through a hose—the atoms of one of the objects (depending on its properties) will give up some electrons to the other object, creating a charge imbalance. If the objects touch repeatedly, as they do when you shuffle your feet on a carpet, more and more electrons will continue to be transferred until the build-up is so great that the electrons will look for ways to flee. If you develop a static charge, for instance, the next time you get near something with a net positive charge, such as a metal filing cabinet, those excess electrons will jump from you to the cabinet and result in a small shock.

Some processes and materials have a greater chance of eliciting sparks. Most plastics, for instance, are insulative materials, meaning electrons cannot easily pass through or across them. Instead, electrons collect more readily on the surface of the materials, gathering a charge. As a result, plastics are difficult to ground, unlike metals, which are conductive and allow electrons to flow freely. Many of the incidents in the Foundation report, for instance, involved filling or storing flammable liquids in static-charged plastic containers.

Another potential danger is pairing these insulating materials with the constant high-speed churning and rubbing common in modern industries like food packaging, printing, and other forms of manufacturing, which can cause static to build quickly if steps aren’t taken to mitigate it. If these processes take place in environments where dust collects in the air, or where there are flammable solvents, inks, or varnishes, the consequences of a spark can be high.

In fact, the Foundation report found that nearly a quarter of all static incidents reported occurred in web and sheet processing facilities—generally where large rollers feed paper, plastic films, fabrics, or other materials through machinery for printing or packaging. There is evidence to suggest that the threat in these facilities could be increasing as new types of plastics are introduced in packaging to better preserve food, and as greater demand compels plant managers to run rolling machines faster or adjust processes to increase output, Robinson said.

The good news, he added, is that methods to eliminate excess static already exist—they just require knowledge and diligence, two things that the Foundation report found are currently lacking at some facilities. A majority of the static incidents found by the research team were caused by “poor management or negligence,” the authors wrote. Either plant officials weren’t aware of NFPA 77, or the information wasn’t followed as intended.

Reworking NFPA 77

To address these findings, one of the technical committee’s primary objectives during the current revision cycle has been to rework the information in NFPA 77 to present it in a more user-friendly way. This is especially true for Chapter 17, which deals with web and sheet processing.

The number of steps required to prevent static discharge “is not an infinite list, it’s completely doable,” Robinson said. “The goal is to make this information more clear and accessible so that someone can pick up NFPA 77 and somewhere early in the book have a checklist that says, ’here are the six things you want to look at.’ And you shouldn’t need an advanced degree to figure them out.”



The first draft of the revised document, which will be posted in March, will include easy-to-follow lists and diagrams to help both managers and factory line workers quickly identify and catch situations that could lead to a deadly spark, such as a roller that isn’t turning properly. Such at-a-glance guidance hasn’t been offered in NFPA 77 before.

Additionally, Robinson and others on the committee believe that routine safety and maintenance checks related to static need to become more common in these facilities, just as they are with systems like fire suppression and alarms. This is especially important, Robinson said, when there is a change to the processes at a factory. Although it is common, and in fact required, for facilities to undergo various assessments of worker safety and system performance when substantial changes are made, static is rarely included in such assessments. “I would like to see some language added to NFPA 77 that says, ’if you’re going to change a process substantially, make sure that static electricity is one of the issues on that list of things to check,’” Robinson said. “This is an example of a practice that is fairly inexpensive and very effective, but it’s not widely practiced. It’s a no-brainer to me—but you know, someone’s got to do it.”

Beyond simplifying some of the information, there are likely to be myriad other tweaks to NFPA 77 resulting from a comprehensive review that was ongoing even before the Foundation report was published last summer. In October 2020, the committee broke into working groups to go through the entire document chapter by chapter, a process that revealed that “every chapter in the document has a good opportunity for clarification and revision,” Robinson said. Among other things, this will likely include adding information on emerging technologies, such as new grounding and bonding methods, and incorporating updated guidance from referenced standards on dust and other flammable substances. When the updated NFPA 77 is published in late 2023, Robinson predicts it will represent one of the most extensive revisions in the 80-year history of the document.

The other main gap identified by the Foundation report—the seeming lack of awareness of NFPA 77’s existence—will be a tougher nut to crack. The NFPA 77 committee is working to identify opportunities to increase awareness of both static hazards and NFPA 77’s guidance, and the results of those efforts will be rolled out over the next few years.

But even if everyone suddenly becomes aware of NFPA 77, or one of the several other static-related codes that exist internationally, it won’t do much good if the information isn’t used. Like everything when it comes to voluntary safety prevention, adoption can be a balancing act between a company’s desire to maximize safety and its obligation to its bottom line. It’s a conundrum that Robinson said he sympathizes with.

“Say I’m running a food packaging line making bags for shredded cheese, and I’ve got orders that exceed the capacity of my machine. Do I buy a new machine, or do I just run the one I have a little faster?” he said. “If I could speed it up by 10 or 15 percent, I could fill these orders, so let’s do that. Of course, when you run a machine faster, the material touches and separates faster and you get more static.”


TRANSCENDENTAL GRAPHICS/GETTY IMAGES

For businesses that have never experienced a static accident, such a trade-off might be an easy choice. But as evidenced by Barton or even the Hindenburg, when conditions do align, the consequences can be sudden and catastrophic. The hope is that a revised and better understood NFPA 77 will provide enough knowledge and incentive to give facilities prone to static hazards a simpler set of choices.

“If the people who are involved have access to the right information, these accidents don’t have to occur,” Robinson said. “Static electricity ignitions are not like acts of God. They’re preventable, not inevitable.”