Incident Description
A hydrocarbon release and subsequent fire and explosions occurred at the Olefins ll unit at the Formosa Plastics Corporation, USA, Port Comfort, TX, complex. A trailer being towed by a fork lift snagged and pulled a small drain valve out of a strainer in a liquid propylene system, forming a large flammable vapor cloud that subsequently ignited. Operators immediately began to shut the plant down and attempted to isolate the leak. They tried to reach and close manual valves that could stop the release; however, the advancing vapor cloud forced them to retreat. At the same time, control room operators shut off pumps, closed valves, and vented equipment to the flare stack to direct flammables gases away from the fire. Immediately after the release, the vapor ignited creating an explosion. The explosion knocked down several operators and burned two others exiting the unit, one seriously. Flames from the fire reached more than 500 feet in the air. Because of the size of the fire, Formosa initiated a site wide evacuation. A total of sixteen employees were injured, one seriously. The extensive damage shut down Olefins ll unit for 5 months. [1]
Lesson Learned:
The need for guidance on remote isolation of equipment to minimize loss of containment and its consequences is clear.
Remote Isolation of Equipment
Remote isolation of equipment containing hazardous material is necessary to mitigate a release of hazardous material when there has been loss of containment. Isolation can be accomplished with the appropriate location of remotely operated emergency block valves (EBVs). EBVs are manual and remotely operated valves that are designed to isolate hazardous material in the event of an emergency. The location of the manually activated push button or manual valve should be in an area away from the potential loss of containment so they can be operated safely. Some valves could also serve as the final element in a safety instrumented system and as an EBV.
Location of emergency block valves
- Remotely operated EBVs should be located such that major process equipment or unit operations can be isolated in the event of a loss of containment. For examples, in one company the olefins plants’ EBVs are typically located:
- At loading/unloading lines in hazardous service;
- At the inlet and outlet of compressors;
- At the inlet and outlet of reactors;
- At the inlet of pumps from vessels with 10,000 pounds of flammable material;
- At major lines entering or leaving a system of vessels, containing more than 10,000 pounds of flammable chemicals, which operate together to perform a unit operation such as distillation, refrigeration or reaction. For example in an ethylene plant, an EBV is often installed in the feed line to a distillation unit and another EBV is installled in the outlet line from the unit to the next process unit;
- At the battery limits for pipelines containing hazardous materials. [2]
Each chemical process should be evaluated so that EBVs are properly located. Some companies use the hazard identification process and layer of protection analysis, or other risk assessment methods to identify the need for EBVs.
Automated Activation
A more immediate response to potential danger can be provided by EBVs which can be activated by a detection system (for example, detectors for a toxic or flammable gas or smoke), situated around a chemical plant. Advantages of automated activation include:
- Elimination of potential operator error;
- More rapid isolation;
- Reduction in calculated releases for risk assessment purposes and consequence of off-site effects. [3 ]
Manual Activation
EBVs may be manually activated by push buttons located at a safe distance from the valve at a location not affected by the loss of containment. Typically the emergency shut off button is a large red, mushroom shaped device. Leak detection may trigger an alarm, usually both in the plant and in the control room, to which the operator can respond by operating the EBV and other systems as necessary. The advantages of manual activation include:
- The value of an operator’s assessment regarding the most appropriate measures for dealing with the leak, including isolation;
- Avoidance of false trips;
- Avoidance of the potential failure of an automatic device. [3 ]
Other EBV issues
- Fireproofing and protection measures are necessary for the valves, cables (power and control) and actuators per API RP 2218.
- EBVs should be mounted directly to vessel nozzles.
- EBVs must be accessible and identified for use in an emergency. They can be painted yellow and labeled with a sign.
- There should be a remote indication of valve positions in the control room.
- The simplest technology should be used to move the valve to the safe state.
- Bypasses should be managed similar to other safety equipment.
- EBVs should be identified on piping and instrument drawings.
- A formal functional testing program requiring documentation and auditing is recommended. There have been incidents when EBVs did not operate when needed because of a lack of a functional testing program to detect malfunction.
- Emergency responders should be trained on the location of EBVs. [4]
References
“Fire at Formosa Plastics Corporation: Evaluating Process Hazards,” U. S. Chemical Safety and hazard Investigation Board, Report No. 2006-01-I-TX, June 2006.
Communication from a company not identified
“Emergency isolation of process plant in the chemical industry”, Chemical Sheet No. 2, Health and Safety Executive, http://www. hse.gov.uk
Communication from a company not identified
“Emergency Isolation,” Health and Safety Executive, http://www.hse.gov.uk. (Reference not cited)
“Approval Standard for Firesafe Valves,” Class Number 7440, Factory Mutual, May, 1981. (Reference not cited)
“Guidelines for Safe Storage and Handling of Reactive Materials,” pages 163,181, CCPS, 1995. (Reference not cited)
Acknowledgements
CCPS wishes to thank John Murphy for authoring this document. We are also grateful to Tim Wagner and Jim Verboon of the Dow Chemical Company, Kelley Keim of Exxon Mobil Chemical Company, Kathy Kas of Rohm and Haas, Stan Grossell of Process Safety and Design, Henry Febo of Factory Mutual, John Baik of BP, and the OSHA and Process Safety Alliance for providing input and peer review guidance.