Some distillation columns in the chemical industry are operated in batch mode with a fairly short operating cycle. At the end of each cycle the columns are cooled and recharged. During the cooling cycle, air will be drawn into the column by the action of a vacuum relief valve.Consequently, for a finite portion of the operating cycle a flammable mixture will exist in the column.Here we maluate the risk posed by such a n operation to see if a mitigation measure is justified. We develop a fault tree and estimate the frequency of ignition by all possible ignition sources. By comparing the risk reduction attainable by installing a lightning protection system with that attainable by using an inert blanketing system the lightning protection system is found to be the preferred solution. It provides about the same risk reduction at a lower overall cost. 16-24 21 purge T ' O t 3 l S (11-15) X 6 + 16-24 99 0.1515 0.1212 0.3939 0.0606 0.0606 0.2121 1.0

Waste‐derived fuel is an environmentally friendly method for destroying waste and recovering the energy value it contains. The fuel is characterized as a mixture of various solvents with a flashpoint in the flammable range. In addition to these solvents, the waste fuel contains solid material. During the transfer of this material to storage tanks, some of the solid material is is left behind in the tankers and rail cars. The ideal solution to remove this solid material is to wash the tank vehicle with the same waste fuel. With the waste fuel being in the flammable range, there is a concern about the washing operation causing ignition due to static electricity. Scaled experiments were conducted to assess the potential for static electricity to cause ignition. Although several ignition mechanisms were assessed, this paper is concerned with the charged mist caused by the high velocity solvent jet impinging on the tank wall. Isopropyl alcohol, mixed xylenes, and mineral spirits were evaluated. An aerosol electrometer was used to measure charge per unit volume of mist sampled. Discharge generation was assessed using an analytical model which estimates electric field corresponding to measured charge density for various configurations.