Chlorine and acetone produce a violent exotherm. In the original design of a reactor that mixed vaporized chlorine and acetone, there was no provision for preventing acetone from backing up into the vaporizer on the loss of Chlorine pressure. As a result, when the chlorine feed was shutoff before the acetone, the acetone backed up into the vaporizer and filled it. Upon restart of the Chlorine, the vaporizer melted and caused a Chlorine emission into the plant. A safety review of this could have identified this problem and put in additional engineering or administrative controls to prevent this problem.

What type of engineering and administrative controls could have prevented the chlorine emission in Example #1? Give an example of each.