Question

Read about the Flixborough disaster that occurred in 1974 ( or watch a video about it on youtube). What was the cause of the accident and what safety lessons are to be learnt from this disaster? (Write no more than 250 words).

Answer 1

The Flixborough, UK, Cyclohexane Disaster, 1 June 1974

Cause of the accident :-

1. Two months before the incident, R-5 was found to be leaking.
2. A 6 ft. long crack had developed.
3. A water hose stream was directed to the crack to cool and quench the small cyclohexane leak.
4. The cooling water contained nitrates which encourage stress corrosion of certain carbon steels.
5. Thus, by trying to relieve the situation, the quenching was actually acting as a promoter of corrosion Ultimately, the reactor had to be removed from service.
6. There was no experienced works manager, WM, available on site at the time of the removal of R-5.
7. The previous WM, a good maintenance engineer with 25 yrs of experience, had quit because an anticipated promotion was given to an outside person.
8. As there was no experienced mechanical engineer on site, those remaining decided to “fast track” or “scratch pad” a solution for the intended by-pass.
9. They sketched a full-scale by-pass line in chalk on the maintenance floor.
10. No stress analyses calculations were performed on the by-pass connection.
11. The by-pass line was quickly installed and the plant put into start-up mode.
12. Shortly after start-up, the by-pass line failed causing 40,000 lbs of cylcohexane to leak into the confined spaces of the reactor support structure.
13. Within two minutes, the vapor cloud exploded.

Lessons to be learnt from this disaster :-

1. The main root cause of this incident was the use of cooling water with nitrates to quench cyclohexane leaks on the reactors.
2. Another root cause was installing a by-pass line, or any line for that mater, without stress analysis. This is a recipe for disaster.
3. A third root cause was management must recognize when they are vulnerable to critical manpower changes.
4. More control is required to conduct good engineering practices once the plant is up and running.
5. Poor location and poor construction of the control room.
6. Plant was too congested at the design stage.
7. Must minimize hazardous inventories.
8. Process hazard review required at regular intervals.
9. Plant must adhere to pressure vessel regulations.
10. Require emergency planning with the community.