An explosion last year at an area Barton Solvents distribution plant was most likely caused by a static spark from a loosely held measuring float, investigators said Thursday.

An explosion last year at an area Barton Solvents distribution plant was most likely caused by a static spark from a loosely held measuring float, investigators said Thursday.

Such floats are used in hundreds of thousands of chemical tanks around the world, according to investigators.

The U.S. Chemical Safety Board, an independent federal agency charged with investigating industrial chemical accidents, released its final report Thursday on the July 2007 explosion at the Barton Solvents plant in Valley Center. The report included a series of recommendations to prevent similar explosions at other chemical tank facilities.

The report said several factors came together on July 17, 2007, to lead to the explosion: the right temperature and humidity, the metal measuring float, how the tank was filled and refilled, and the ignitable vapor-air mixture inside the storage tank.

“We believe it was a low-probability, high-consequence event,” said lead investigator Randy McClure.

The blast destroyed much of the plant and led to widespread evacuations of Valley Center, a town of 6,000 just north of Wichita. Eleven residents and one firefighter were injured.

David Casten, president of Des Moines, Iowa-based Barton Solvents, said his company is now modifying 135 floats in chemical tanks in its plants.

“Overall we are pleased,” Casten said of the board’s investigation. “They repeatedly said it was an accident.”

It was important to the company investigators did not find negligence, he said.

The Chemical Safety Board also found that standard industry practices for bonding and grounding chemical tanks may not be enough to prevent fires sparked by static electricity.

The tank where the first explosion occurred had built up so much pressure the bottom seam separated and the tank launched 130 feet into the air, investigators said. Within moments, nearby tanks also ruptured, with debris hitting a nearby mobile home and business.

“We believe if the tank farm had been designed appropriately, this would not have been anything but a single tank fire,” McClure said, noting the tanks at the Barton Solvent facility were closely spaced and not properly vented.

Casten later told reporters the Valley Center facility had been built to industry standards when the tanks were installed in the mid-1950s.

Investigators sifting through the debris after the explosion found one of the blown measuring floats and concluded a spark likely jumped between the metal parts and ignited the explosive mixture of vapor and air that had accumulated above the liquid.

“It was definitely a ‘eureka’ moment,” McClure told reporters.

The float manufacturer has posted a warning on its Web site and is now modifying its design.

The Chemical Safety Board recommended that Occupational Safety and Health Administration improve the information in its material safety data sheets to include nonconductive flammable liquids. It also recommended that major industry associations warn their members that these materials can accumulate static electricity.

Other recommendations to companies include purging their storage tanks with an inert gas to remove oxygen, adding antistatic agents to liquids, pumping liquids more slowly and verifying that measuring floats are bonded.

McClure said an Oct. 29, 2007, explosion at another Barton Solvents plant in Des Moines, Iowa, also was caused by a static charge but the two blasts had little else in common.

The Iowa explosion was caused by a static spark from the nozzle filling a small portable container that was not bonded or grounded properly or approved for flammable liquids, McClure said.