3. The Need for Process Safety
3.11 Management of Change: Flixborough Explosion, UK, 1974
Emergency Response (Section 2.17). The Formosa Plastics VCM explosion also illustrates the importance of emergency response planning. When the VCM release occurred, gas detectors in the building activated and operators responded by trying to mitigate the release. The proper response to this activation should have been to evacuate.
Measurement and Metrics (Section 2.19). There had been two previous incidents at Formosa Plastics plants that involve operators opening the wrong valves. These incidents and their lessons were not shared with the other plants. A metrics system that tracked leading and lagging indicators, as described in Section 2.19, could have alerted Formosa Plastics to a systemic problem and enabled the company to take steps to correct it. These actions could have been to train operators at all plants about why bypassing the interlocks was dangerous and/or placing a guard over the hose connection to prevent overriding the interlock without proper review and authorization.
3.10.5 References and Links to Investigation Reports
CSB 2007, U.S. Chemical Safety and Hazard Investigation Board, Investigation Report, Vinyl Chloride Monomer Explosion, Report No.
2004-10-I-IL, March 2007.
U.S. Chemical Safety and Hazard Investigation Board, Video – Explosion at Formosa Plastics, 2007, (http://www.csb.gov/formosa-plastics-vinyl- chloride-explosion/)
3.11 Management of Change: Flixborough Explosion, UK,
vessels arranged in series, each set 360 mm (14 inches) below its predecessor to allow the flow to progress through the reaction train by gravity.
On March 27, 1974, a crack was detected on Reactor No.5. A Maintenance Engineer recommended complete closure for 3 weeks. The Maintenance Manager, whose job had been filled for several months by the head of the laboratory while awaiting a reorganization of the company, proposed dismantling Reactor No. 5 and connecting numbers 4 and 6 together by a 500 mm (20 inch) diameter temporary connection. To support the piping, the proposal was to use a structure made from conventional construction industry scaffolding, Figure 3.23.
The temporary connection was not adequate for the forces and temperatures involved, and failed, releasing 30 metric tons of cyclohexane in 30 seconds. Of the 28 employees killed, 18 were in the control room. The loss of life could have been far higher if the incident had occurred on a weekday, and not on a Saturday, when the number of day employees on site was low. The whole plant was destroyed. The neighboring housing was devastated. The fire lasted over three days with 40,000 m (10 acres) affected. See Figures 3.24 through 3.26 (CCPS, 2008).
Figure 3.23. Schematic of Flixborough piping replacement, source Report of the Court of Inquiry.
Figure 3.24. The collapsed 20 inch pipe.
Figure 3.25. Damage to Flixborough plant.
Figure 3.26. Damage to Flixborough control room.
3.11.3 Cause
The design of the replacement pipeline was inadequate, leading to its failure. The investigation found that “No consideration was given to the bending moments or hydraulic thrusts that would be imposed on the assembly due to its dogleg design.
There was no reference made to vendor manuals for the expansion bellows, nor to relevant British Standards. No drawing was made for the design.” (Source, Court of Inquiry, 1975).
3.11.4 Key Lessons
Management of Change (Section 2.14). Changes to a process or equipment must be reviewed and implemented by people with knowledge appropriate to the situation. This incident is important in the history of process safety as the prime example of the importance of an MOC program. There was no engineering review of this change at all. As seen in the cause section, important mechanical design features were not considered during the change.
Flixborough highlights the importance of Management of Organizational Change (MOOC) as well as physical change. At Flixborough, “the works engineer had left early in the year and had not yet been replaced. At the time the bypass line was being planned and installed, there was no engineer on site with the qualifications to perform a proper mechanical design, or to provide critical technical review on related issues. There were chemical and electrical engineers
on staff, but no other mechanical engineers.” A statement often used in relation to the modifications at Flixborough is that “they didn’t know what they didn’t know”.
Although the presence of a mechanical engineer may not have changed the outcome if no MOC review was held at all, it is more likely that the significance of the change could have been recognized by someone at the plant. MOOC covers modification of working conditions, personnel turnover, task allocation changes, organizational hierarchy changes, and organizational policy changes. Guidelines for Managing Process Safety Risks During Organizational Change (CCPS 2013) covers this topic in more detail.
Codes and Standards (Section 2.3). As stated in the summary, the site office building was destroyed. At the time, 1974, there were no standards in place with respect to facility siting and layout. This event is an example of why there is now such a standard, API RP 752, Management of Hazards Associated with Location of Process Plant Buildings.
3.11.5 References and Links to Investigation Reports
CCPS 2008, “Incidents That Define Process Safety”, American Institute of Chemical Engineers, New York, NY, 2008.
CCPS 2013, “Guidelines for Managing Process Safety Risks During Organizational Change, American Institute of Chemical Engineers, New York, NY, 2013.
CCPS Process Safety Beacon, Flixborough – 30 Years Ago, June 2004 (http://sache.org/beacon/files/2004/06/en/read/2004-06%20Beacon-s.pdf) CCPS Topics, Incident Summary: Flixborough Case History
(http://www.aiche.org/ccps/topics/elements-process-safety/commitment- process-safety/process-safety-culture/flixborough-case-history)
Her Majesties Stationary Office, The Flixborough Disaster – Report of the Court of Inquiry, 1975.
API RP 752, Management of Hazards Associated With Location of Process Plant Buildings, 3rd Edition, American Petroleum Institute, December 2009.