CSB Report Calls for Improved Nonconductive Flammable Liquid MSDSs

In a new case study addressing the July 2007 explosion and fire at the Barton Solvents distribution facility in Valley Center, Kans., the U.S. Chemical Safety Board (CSB) determined that a static spark resulting from a level-measuring float inside the tank likely caused the explosion and called for improved material safety data sheets (MSDSs) for nonconductive flammable liquids.

The July 17, 2007 explosion and fire destroyed the Barton facility, led to the evacuation of 6,000 residents and caused 11 residents and one firefighter to seek medical attention. The incident involved nonconductive flammable liquids, which can accumulate and maintain static electrical energy that discharges more slowly than from more conductive liquids. Some of these liquids can form ignitable vapor-air mixtures inside storage tanks, and can explode if a spark occurs.

Hidden Danger

CSB investigators found that on the day of the explosion, a tanker-trailer arrived to transfer the nonconductive flammable liquids Varnish Maker's and Painter's Naphtha (VM&P Naphtha) into a storage tank. While the transfer equipment from the truck tanker to the storage tank likely was properly bonded and grounded to prevent the generation of static electricity, CSB found that the float device inside the 15,000-gallon storage tank presented a hidden danger.

The device, a metal float linked to a metal tape measure, was used to measure the liquid level. CSB determined that a static electrical charge in the liquid was generated by the flow of the solvent pumped from the trailer into the storage tank, and by stop-and-start filling that introduced air into the liquid, resulting in bubbles and turbulence.

At the same time, the space above the liquid was being filled with an explosive mixture of vapor and air. CSB determined that the liquid flow and turbulence created by the tank filling likely resulted in the metal float accumulating a static electrical charge. As the float moved, a gap is believed to have formed within the linkage of the tape and the float. CSB investigators said a spark likely jumped between the metal parts and ignited the explosive mixture of vapor and air that had accumulated above the liquid.

The explosion blew the tank 130 feet into the air, and within moments two more tanks ruptured and released their contents. As the fire burned, the contents of nearby tanks were released and ignited, launching debris into the air where some of it struck a mobile home and a neighboring business.

"While we found the most likely cause of the Barton explosion was sparking across the float linkage, we emphasize that explosions can occur in tanks without faulty floats when there is a discharge from the build-up of static in the nonconductive flammable liquid itself,” said CSB board member William Wark.

MSDS Recommendations

CSB determined the MSDS for the VM&P Naphtha did not adequately describe the explosive hazard or the precautions necessary to prevent ignition from static electricity. Most of the MSDSs for the flammable solvents supplied to Barton indicated that the solvent could accumulate a static charge, which could spark and ignite vapor. But the MSDSs did not warn that the solvent could form a highly explosive vapor-air mixture inside a storage tank.

CSB reviewed 62 MSDSs for some of the most widely used nonconductive flammable liquids in industry, such as VM&P Naphtha, hexane and toluene. Most failed to recommend specific precautions beyond bonding and grounding.

“The accident at Barton Solvents emphasizes the need for accurate and detailed MSDSs,” said Wark. “We found that while most MSDSs for this category of flammable liquids do warn about the dangers of accumulating static electricity because the liquids are poor conductors, the MSDSs do not warn specifically that they can be ignited in storage tanks.”

CSB issued recommendations to OSHA and trade associations to improve required information contained in MSDSs to include addressing nonconductive flammable liquids, which routinely are shipped to distributors such as Barton. CSB also recommended that six major oil and chemical industry associations ask their member companies to improve the warnings on the MSDSs of flammable liquids because these materials can accumulate static electricity.

CSB also suggested additional safety measures for companies that handle such liquids:

  • Obtain more detailed additional technical information on the liquids from manufacturers that may not be found on MSDSs.
  • Purge storage tanks with an inert gas to remove oxygen.
  • Add anti-static agents to the liquids.
  • Pump liquids more slowly.
  • Verify that storage tank level floats are effectively bonded.

CSB released a 10-minute safety video that features a computer animation depicting the sequence of events that led to the Barton explosion and fire. The video, “Static Sparks Explosion in Kansas,” can be downloaded at http://www.safetyvideos.gov.

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