HSE Sharing

What is the top event of the TPC Group incident?

• Popcorn polymer formation in a dead leg

• Pipe rupture caused by pressure buildup 

• Explosion due to butadiene vapor cloud ignition

• Fire caused by equipment overheating 

Answer explanation

• A is Incorrect: While popcorn polymer formation was a contributing factor, it wasn’t the final event.

• B is Incorrect: The pipe rupture led to the explosion but wasn’t the top event.

• D is Incorrect: Fire occurred after the explosion, not as the primary event. 

Why did this incident happen?

• A known safety hazard (popcorn polymer) was poorly managed. 

• Workers failed to isolate the pipeline properly. 

• The plant lacked fire suppression systems. 

• Butadiene was stored at excessive temperatures.

Answer explanation

• B is Incorrect: The pipeline was isolated correctly, but it wasn’t drained or inspected afterward.

• C is Incorrect: Fire suppression systems were not relevant to the root cause of this incident.

• D is Incorrect: Butadiene was not stored improperly; the issue was stagnant material in a dead leg. 

What is a "dead leg" in a piping system?

• A section of pipe that is not in active use but still contains material 

• A damaged section of pipe that leaks chemicals 

• A temporary pipe used during maintenance activities 

• A section of pipe used only for drainage purposes

Answer explanation

• B is Incorrect: Dead legs are not necessarily damaged or leaking.

• C is Incorrect: Dead legs are permanent sections of piping, not temporary ones.

• D is Incorrect: Dead legs are not specifically for drainage; they are stagnant sections. 

What substandard actions led to this incident?

• Pipeline isolation without proper draining or purging 

• Prolonged stagnation of butadiene in an unused pipeline due to delayed maintenance work 

• Lack of inspection or monitoring of stagnant pipelines (dead legs) 

• All of the above 

Answer explanation

All options contributed to the incident: 

• The pipeline was isolated but not drained or purged, leaving butadiene stagnant. 

• Maintenance work on a connected pump was delayed, prolonging stagnation in the dead leg. 

• There were no inspections or monitoring systems for dead legs.

Why did no one detect the growing risk in the dead leg over 114 days? 

• No inspections were conducted on the pipeline during this time. 

• There were no sensors to monitor pressure or polymer buildup in stagnant lines. 

• The risk of popcorn polymer formation was underestimated by operators. 

• All of the above. 

Answer explanation

All options contributed: 

• A & B: Lack of inspections and sensors meant no one noticed pressure buildup or polymer growth. 

• C: Operators underestimated how quickly popcorn polymer could form under stagnant conditions. 

What caused popcorn polymer to form in the dead leg? 

• Excessive heat from nearby equipment triggered polymerization. 

• Stagnant butadiene reacted naturally over time due to lack of flow. 

• Workers added an incorrect chemical that triggered polymerization. 

• Corrosion inside the pipe walls caused popcorn polymer formation. 

Answer explanation

• A & C is incorrect: There’s no evidence that heat or added chemicals triggered polymerization.

• D is incorrect: While corrosion can occur in stagnant pipes, it wasn’t directly responsible for popcorn polymer formation. 

What caused the pipe to rupture?

• Corrosion weakened the pipe walls over time    

• Excessive pressure buildup from expanding popcorn polymer

• High temperatures caused thermal expansion in the pipeline

• Improper welding during previous repairs 

Answer explanation

• A & D is incorrect: Corrosion and welding issues weren’t mentioned as causes. 

• C is incorrect: No evidence suggests high temperatures contributed to this incident. 

Why did the release lead to an explosion?

• Butadiene vaporized upon release and formed a flammable vapor cloud that ignited.

• The released butadiene reacted violently with water nearby.

• Heat from nearby equipment caused spontaneous ignition of liquid butadiene.

• Butadiene reacted with oxygen inside the pipeline before release.

Answer explanation

• B & C is incorrect: There’s no mention of water or heat causing ignition.

• D is incorrect: The reaction occurred after release, not inside the pipeline. 

What management system failure allowed this incident to happen?

• Lack of inspection and monitoring for dead legs during operations

• Permit-to-Work (PTW), which failed to enforce draining requirements

• Inadequate prioritization of maintenance work on critical equipment

• All of the above

Answer explanation

All options contributed: 

• A & B: Dead legs were not inspected or drained after isolation. 

• C: Delayed maintenance prolonged stagnation and increased risks. 

What is a key lesson learned from this incident?

• Management systems must address risks during both design and operational phases, including maintenance activities.

• Dead legs are unavoidable, so they do not need monitoring or inspection if isolated properly.

• Popcorn polymer only forms under extreme conditions, so it is not a common hazard.

• Inhibitors alone are sufficient to prevent polymerization risks without other controls in place.

Answer explanation

• B is Incorrect because dead legs require monitoring even when isolated. 

• C is Incorrect because popcorn polymer can form under normal conditions. 

• D is Incorrect because inhibitors alone are insufficient without systemic controls.