Low sulphur, high static

In June, 2010, a New Mexico Border Patrol station experienced something you probably don’t want to experience if you do a lot of transferring fuel; they witnessed an above-ground fuel storage tank explosion, one which was fairly well documented by both the local authorities as well as the tank manufacturer themselves.

The U.S. Association of Equipment Manufacturers has released an information sheet detailing the risks of static explosion in diesel fuels and steps you can take to reduce the danger. The sheet is available for download at www.aem.org .

The tank itself was being refuelled with diesel that morning, early enough that it was before things got too hot that summer day. The two men standing by the tank were, in fact, injured (one just experienced ringing in the ears) though not seriously hurt. Part of their survival was due to the concrete surrounding the tank, thought the authorities at the time. ConVault, the company who manufactured the tank, quoted local fire inspector Captain Kellen Tarkington, who said, “The concrete really did its job because if it had been a plain steel tank they would probably both be dead.” Pictures of the AST show basically a cracked concrete rectangle with a shattered roof and exposed rebar that looks like it’s been through an earthquake.

Captain Tarkington noted several things about the explosion in the incident report. Calling the explosion accidental, he speculated that the fuel tanker’s fill hose may not have been properly bonded and grounded, the drop tube was not metal but fibreglass, and the drop tube ended 10 inches from the bottom tank. There were already six inches of fuel in the bottom of the tank, and he speculated that the explosion may have been caused by the drop and the four-inch air gap, leading to some sort of reaction due to static electricity.

It’s the threat of static electricity that lead to recent Association of Equipment Manufacturers’ Best Practices Guidance Bulletin, 6/13, three years later, specifically cautioning people who use diesel fuel, how it’s changed over the years and what handlers need to know about it. The bulletin wasn’t inspired by any rash of explosions in particular, said spokesmen for AEM. Rather, it’s just a way to promote best practices.

There are armies of men and women that spend their days looking to improve the products so important to our daily lives—like fuel—to make them safer, to make them more efficient and to make them cleaner.

Fuel is something that scads of people (scientists, legislators, etc.) have been trying to make cleaner for several generations now. In particular, diesel fuel has undergone some drastic change in its makeup over the last few decades, specifically with the amount of sulphur found in diesel fuel. But it’s the changes to the fuel, making it cleaner, that also make it more potentially vulnerable to static electricity. The industry has taken steps to counter this vulnerability, but those haven’t always been effective.

Says the AEM info sheet, “The removal of sulfur and other compounds in Ultra Low Sulfur Diesel fuel decreases its conductivity and increases its ability to store static charge. Refineries may have treated the fuel with a static dissipating additive. However, there are many factors that can reduce the effectiveness of the additive over time.”

“They found out along the way that the additives get stripped every time you filter it,” said the AEM’s Mike Weber, manager of technical and safety services.

About a decade ago, the standard was low sulfur diesel. Low sulphur diesel had 500 ppm (in sulfur content), but in an effort to get even cleaner-burning diesel, low sulphur diesel has been gradually phased out in North America, starting from about the year 2005, depending on the jurisdiction and the usage (highway, non-highway). Sulphur is/was a major source of particulate matter in diesel fuel, and it lead to the fumes, the soot and all the other pollution associated with diesel.

In an effort to cut pollution levels, we now have ULSD, ultra-low sulphur diesel, which is 15 ppm.
Depending on the jurisdiction, and the continent, dealers have not been able to sell anything but ULSD for the past several years or so, in North America.

According to the US EPA website, “The cleaner diesel fuel program significantly reduces sulfur content, creating immediate health benefits, and allowing engine manufacturers to begin using advanced emissions control systems that further reduce harmful emissions.”

Of course, different countries have different schedules. This summer, Jamaica is taking the ULSD plunge, making it mandatory in their vehicles from the end of June onwards.

“The ULSD is expected to preserve our environment and make our vehicles last longer as sulphur contains pollutants. So lower sulphur means less exhaust and cleaner air,” Jamaica Energy Minister Phillip Paulwell was quoted in the Jamaica Observer as saying.

That changeover comes with a cost. The Observer also quoted Telroy Morgan, a production manager of Petrojam, as saying, “The ULSD will be sold at 10 per cent above the cost of regular diesel. The price is higher but efficiency is greater.”

Along with more pollution-conscious design of vehicles, when paired with the ULSD, it sort of makes a one-two punch for reducing the amount of pollution.

According to the website How Stuff Works, “The process is similar to a self-cleaning oven’s cycle: a filter traps the tiny particles of soot in the exhaust fumes. The filter uses a sensor that measures back pressure, or the force required to push the exhaust gases out of the engine and through to the tailpipes. As the soot particles in the particulate filter accumulate, the back pressure in the exhaust system increases. When the pressure builds to a certain point, the sensor tells the engine management computer to inject more fuel into the engine. This causes heat to build up in the front of the filter, which burns up the accumulated soot particles. The entire cycle occurs within a few minutes and is undetectable by the vehicle’s driver.”

But, as the old saying goes, for every action, there’s a reaction. As mentioned, the ULSD is, in fact, more expensive, due to the processes that it has to go through to remove the sulphur. Also, ULSD is considered to have a lower energy content.

And then there is the aforementioned danger of fires, due to static electricity. According to the AEM’s Best Practices Guidance Bulletin, “Ultra Low Sulfur Diesel… poses a greater static ignition hazard than earlier diesel formulations with higher sulfur content. Avoid death or serious injury from fire or explosion; consult with your fuel or fuel system supplier to ensure the delivery system is in compliance with fueling standards for proper grounding and bonding practices.”

A way to be cautious is to ensure that the entire system (hose, nozzle, tank, pump, etc.) with which an operator is using to refuel is properly bonded and grounded. One issue may be the type of material the refuelling agent uses.

“Gas stations and convenience stores are all going to fibreglass, you can build up a charge (in the fuel) with non-metallic systems,” says Bob Tatnall, president of the Delaware-based fuel research firm Fuel Right. “Fuel in motion builds up a charge with plastic materials.”

Tatnall also said that the danger isn’t so much older versus newer refuelling systems.

“Older systems can generally be metallic, and if it’s buried, it tends to be grounded,” he said.

The AEM’s Mike Pankonin, senior director of technical and safety services, emphasizes the bonded and grounded part. His main message is, “Make sure everything is strictly bonded and grounded, and that the equipment has appropriate fittings.”

Furthermore, since diesel is so hard to light, Tatnall wonders if situations like what happened in New Mexico is because of both static electricity and fuel cross-contamination. But Tatnall also speaks to the inconsistency of approaches to safety, industry wide.

“It is very inconsistent in the States; some fuel merchants feel (precautions are) necessary, some don’t,” he says. “But where you have multifuels, they tend to have stronger requirements.” 

However, judging by the AEM’s response to their bulletin, the word is getting out. Weber says that the material that the AEM has recently released on ULSD has the “second-most hits during the month of June.” And additional endorsing organizations are wanting in, apparently, too.

“Awareness is the key word,” said the AEM’s Pankonin.

And “safety” is the other.