An oil refinery located in a major metropolitan area used a hydrogen fluoride (HF) alkylation process. HF is a liquid at ambient conditions, but, on release to the atmosphere, it forms a highly toxic vapor cloud which can remain at ground level and drift for a long distance. Moreover, if it comes into contact with water it forms highly corrosive hydrofluoric acid.
HF was delivered to the refinery about once a month by tank (rail) car. Operators connected the tank car to the HF storage tanks using special hoses and fittings. It was critical that there not be a leak during the unloading process.
Management was implementing a process safety program at the refinery. They decided, sensibly enough, to start by conducting a HAZOP (Hazard and Operability Study) on the alkylation process and its related activities — including the tank car unloading operation since this was such a high risk area. (The refinery was an old one and HF had been unloaded from tank cars many, many times. There had never actually been a significant release of HF from any part of the process).
As part of its analysis the members of the HAZOP team asked for a copy of the Unloading Procedures so that they assess the risks associated with this activity. It turned out that those procedures had “gone missing” — no one knew where they were. Eventually, after a day of hunting through files the unit supervisor proudly produced the missing document and shared it with the HAZOP team. A careful evaluation of the procedures, including a field walk-through, showed that — were they to be followed as written — there would be a release of HF. This was not a “maybe”, it was a “will be” — the event was a certainty.
Naturally the HAZOP team recommended that a new set of procedures be written. During the writing of the new procedures it was found that there were some unacceptable inherent hazards associated with the unloading process, so new piping and fittings were installed. Consequently,the risk associated with this operation was substantially reduced.
But the fact that the refinery operators had been able to conduct this high-risk activity safely for so many years highlighted the need to capture practical experience, as discussed in various other Safety Moments in this series, including the following: