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Du Pont Chemical Plant - Coggle Diagram
Why it happened?
No safety analysis was performed on the ventilation system and the ability of the ventilation fans to handle toxic chemical releases was not evaluated
No safeguards such as heat tracing were in place and no formal procedure was developed to dissociate the hydrate in a safe manner.
Failure to maintain safety critical equipment. Two ventilation fans were not in working order at the time of the incident
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Lack of safety hazard analysis performed on the troubleshooting techniques that personnel used to clear the hydrate blockage prior to the chemical release incident
No formal procedure was written for the techniques that were decided on to clear the plugging in the piping
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Poor safety culture. Employees became used to the smell of methyl mercaptan and did not possess the safety knowledge regarding the hazards that methyl mercaptan presented
Employees became accustomed to smelling methyl mercaptan on a daily basis and experiencing no ill health effects leading employees to view methyl mercaptan as a low risk hazard and accepted the alarms as normal
Operations personnel wrongly troubleshoot the high pressure issue in the piping in the manufacturing building
System life cycle
Basic Engineering - A detailed process design is created including equipment and piping system. Basic automation and instrumentation is selected. A preliminary layout design including utilities and waste minimisation is developed. A hazard and operability study is conducted.
Failures - The design layout is unsuitable for the process. Size of the heating/cooling system is inadequate for the task. Incorrect data for automation and instrumentation system is selected. Failure to take in to consideration the corrosion of metals from the chemical process. Unsuitable component design.
Detailed Engineering - A detailed layout and piping design is developed. A full design of automation and instrumentation is created. Structural and civil engineering is conducted. Mechanical design of the equipment is undertaken as well as the electrical design of the plant.
Failures - Unsuitable layout design. Inappropriate automation and instrumentation systems selected. Insufficient lighting system throughout the plant. Failure to design a fail-safe or back-up systems into the overall system.
Preliminary Engineering - Flowsheet is developed to visualise the steps of the process. The different unit operations are selected. A preliminary sizing of the equipment to be used is conducted. A preliminary selection on the material to be used in the construction of the plant is made. The site for the plant is selected. The specifications of the final product are created. A feasibility study is conducted.
Failures - The unit operations selected are unsuitable for the process. Incorrect selection of the sizing of equipment and the construction material contributing to unsafe working conditions. Incorrect specifications for the final product are calculated.
Fabrication, Construction and Installation - A call for tender is issued for the contract to build the plant an a contractor is selected. The plant is built with equipment and electrical systems installed. The plant is inspected and tested and changes are made if required.
Failures - Poor quality parts used to cut costs. Poor workmanship and incorrect installation of equipment. Sensors and instruments poorly positioned. Poor accessibility design. Lack of supervision during the construction of the plant. Poor communication between contractors, designers and plant owner.
Research and Process Development - The idea is generated and the process created. Laboratory studies are conducted and simulation tests are performed on reaction mechanisms and kinetics.
Failures - Incorrect data collected from the studies and simulation tests performed on the reaction mechanics and kinetics.
Commissioning and Operation - Implementation of a safety management system. Continue to optimise and improve procedures. Ongoing training and gaining experience.
Failures - Poor management system in place. Inexperienced workers employed to run the plant. No safety analysis performed. Poor safety culture within the organisation. A lack of inspections/maintenance performed on the plant and equipment. Lack of communication between management/supervisors/workers.
Decommissioning - Decontamination of the system through means of washing, heating, chemical treatment or mechanical cleaning. Dismantling of equipment for inspection. Dismantled components are decontaminated again and the process repeated until components meet the decontamination criteria. Equipment can then be disposed of or transported to another plant to be assembled for further use. Generated waste from the decontamination process is disposed of by approved methods
Failures - Poor decontamination procedures performed. Equipment not fully dismantled and decontaminated. Components not suitable for reuse being used in reassembly of equipment at another plant. Generated waste not being disposed of according to the approved methods.
What happened?
Saturday, 15 November, 2014. The blocked piping is cleared after the hot water warmed the piping enough to cause the solid hydrate to dissociate. With the alignment of the open valves, methyl mercaptan flowed into the waste gate vent header inside the manufacturing building
The waste gate vent header is not designed for methyl mercaptan which resulted in alarms sounding for high pressure in equipment inside the manufacturing building. Operations personnel do not realise methyl mercaptan has flowed into the piping in the manufacturing building and attribute the high pressure to process condensate accumulating in the vent header piping
To warm the piping, hot water is poured over the outside of the methyl mercaptan piping in an attempt to break up the solid hydrate. Technical Team realises that methyl mercaptan expands when heated so to avoid over pressurising the piping, valves are opened by operations personnel between the methyl mercaptan piping and a waste gas vent header which aligned a pathway for methyl mercaptan to enter the piping inside the manufacturing building
Standard practice to relieve the high pressure issue was to manually drain the vent header inside the manufacturing building. A supervisor and worker 1 enter the manufacturing building to manually open two sets of valves on the third floor, releasing the methyl mercaptan that had filled the piping and killing the supervisor.
Friday, 14 November, 2014. Troubleshooting efforts are ongoing. The Lannate Unit Technical Team meet with with operations personnel to discuss troubleshooting options. They identify through technical standards that a solid hydrate can form at low temperatures when mixed with water
Sensors detect the methyl mercaptan in the air and sound alarms. The control board operator is focused on solving the high pressure issue and does not realise that a dangerous chemical leak has occured
Wednesday, 12 November, 2014. Control operators try to restart the Lannate process. Clathrate hydrate forms during the shutdown in the methyl mercaptan piping to the reaction section of the process, blocking the piping. Operators, unaware of the cause of the blockage, begin troubleshooting to identify the cause and clear the piping
Worker 1 uses the radio to make an urgent call for help. Three workers rush to the manufacturing building to assist. None of the workers have knowledge of the methyl mercaptan release and therefore do not wear breathing apparatus into the manufacturing building
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Worker 2 transcends to the third floor and is overcome by methyl mercaptan and is killed. Worker 3 transcends to the fourth floor and finds no one, makes his way to the stairwell and loses consciousness. Worker 4 transcends to the second floor where he is overwhelmed by methyl mercaptan and he retreats to the stairwell
Monday, 10 November, 2014. Operating difficulties are caused by a chemical dilution and the plants Lannate unit is shutdown
A fifth worker grabs three 5-minute respirators and enters the manufacturing building after ignoring warnings not to enter the building. Worker 5 finds worker 4 in the stairwell and places a respirator over his face. Worker 4 recovers and exits the building. Worker 5 then activates the fume release alarm to alert all workers of the chemical release in the manufacturing building
Worker 5 transcends to the third floor and retrieves a self-contained breathing apparatus. He is overcome by the methyl mercaptan while trying to save worker 2 before he connects his respirator to the SCBA.
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Design failures
No safety analysis was performed on the ventilation system and the ability of the ventilation fans to handle toxic chemical releases was not evaluatedThe buildings ventilation system was ineffective and did not provide adequate ventilation in the building
The design of the vent piping leading to the reduced scrubbed incinerator did not address the problem of liquid accumulation in the waste gas vent header vapour piping
No safety measure such as audible or visible alarms in buildings to alert workers of potentially toxic environments
The waste gate vent header was not designed for methyl mercaptan. With an alignment of certain valves, methyl mercaptan was able to flow through piping into the waste gate vent header
Operating procedures not clearly defined as to the procedure for entering a building with "restricted access" or require personnel to wear breathing apparatus when entering a restricted access area
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The manufacturing building was of poor design and only increased the risk of hazards by confining toxic chemical gases inside
The alarms for toxic chemical sensors are only seen at the control panel in the control room. No alarms are positioned in the building or on the exterior of the building to alert employees
System parts
Residents of La Porte, Texas
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Chemical Plant in La Porte, Texas
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