(198g) Deflagration Incident in an Organic Peroxide Solution Tank

A deflagration occurred inside of a vessel at an Ashland plant on February 24, 2017. The vessel was charging a catalyst solution of deionized water, a hydroperoxide to a reactor. The incident occurred as the catalyst solution transfer was ending and the water rinse was beginning. Fortunately, there were no injuries or chemical exposures as a result of the incident since no personnel were in the area at the time. The vessel was damaged during the incident, and the consequences could have been more severe. A pressure of approximately 25 psig was reached during a laboratory experiment that replicated the incident. The hinged lid, which also serves as a relief device, successfully vented the deflagration and prevented a vessel rupture. The root cause of the incident was an overcharge of sodium hypochlorite solution to the deionized water system and subsequent reaction of the sodium hypochlorite with the hydroperoxide.

A VSP2 apparatus was used to generate material for sampling. A mild exotherm and pressure rise was observed when the hydroperoxide was added, with a net pressure increase of 49.2 psi. Based on the test cell vapor space volume of 40 ml, it is estimated approximately 0.0054734 moles of non-condensable gas was generated during the experiment. The oxygen concentration of the gas generated by decomposition is 93.68 vol% oxygen. The minimum ignition energy of the vapor was measured in accordance with ASTM E582, Standard Test Method for Minimum Ignition Energy and Quenching Distance in Gaseous Mixtures. The testing result was a measurement of 0.015 mj.

A charged water slug mechanism was investigated as a possible ignition source for Ashland’s mixing tank explosion. The mechanism was initially thought to be implausible since the upset condition. While ignition via a spark from a single water slug is unlikely, the rinsing operation would have generated a large number of successive slugs each of which would have some likelihood of producing a static discharge. Each discharge would encounter a different gas composition and so it’s quite possible that the worst case gas composition would have been encountered by at least one slug.