East Palestine vent and burn: what the February 2023 record said, and what the 2024 board finding adds

Board date June 25, 2024
Final report findings (EP2), text from the corrected reissue of July 23, 2024

This report was reissued on July 23, 2024, with corrections to the description of the tank car TILX402025 lease

The note places the corrections on report pages 57 to 58, outside the excerpts used here. The findings below carry the June 25, 2024 board date.

Bearing: the actual finding

The National Transportation Safety Board determines that the probable cause of the derailment involving Norfolk Southern Railway train 32N was the failure of the L1 bearing on the 23rd railcar in the consist that overheated and caused the axle to separate, derailing the train

A reading of 253°F above ambient is the maximum reading for the type of HBD installed at MP 49.81; the actual temperature may have been higher.

The HBD transmitted a non-critical alert to the advanced train control (ATC) desk about the temperature of the L1 bearing but, as designed, did not broadcast an alarm to the train’s crew.

Tank car shell measurements, February 5 to 6, 2023

Across the period: first reading 135, last 126, change -9 °F over 22 h 30 min. Highest reading apart from the fire-coincident 139: 138 at 5:00 p.m. on February 5; change from there to the last reading: -12 °F over 21 h 30 min. Lowest: 120 at 7:00 a.m. on February 6. 18 of 21 rows carry a value.

When interviewed by the NTSB, the EPFD fire chief noted that this increase in temperature coincided with the ignition of a small fire underneath tank car OCPX80370, and that the temperature decreased after the fire was extinguished.

By the time of the meetings on February 6, the highest tank car temperatures had fallen from about 138°F the previous afternoon to about 126°F.

This increase to 138°F on the afternoon of February 5 was close to the highest temperature recorded on a tank car shell (139°F, measured during a brief fire under the tank car about midnight on February 5-6).

Polymerization and the vent and burn justification

26. The observed downward temperature trend in tank car OCPX80370 indicates that polymerization was not occurring within the tank car, contrary to the representation by Norfolk Southern Railway and its contractors.

27. The vinyl chloride monomer within the derailed DOT-105 tank cars remained in a stabilized environment until the vent and burn and did not undergo polymerization; the vent and burn procedure was not necessary to prevent a polymerization-induced tank rupture.

According to information Oxy Vinyls provided the NTSB after the vent and burn, a runaway polymerization reaction would produce “a rapid, significant, and sustained increase in temperature and pressure.” The dashed red trendline in the figure shows a gradual decline instead.

Evidence available after the vent and burn also does not support polymerization. During the vent and burn, all five VCM tank cars expelled material, indicating that the cars were still under positive internal pressure.

Finally, Oxy Vinyls performed laboratory analyses on residue samples recovered from the interiors of the VCM tank cars. While these analyses did not definitively rule out the presence of PVC (VCM and PVC are chemically similar) they did not find evidence of PVC.

The residue analysis is not conclusive on its own: the report says it did not definitively rule out the presence of PVC (NTSB final report, corrected, PDF p. 164).

Documented communication path to the incident commander

Attributed quotations only. The excerpts do not state why anyone communicated or did not, and this page does not guess.

1. NS to incident commander and NTSB on scene: 3°F increase on OCPX80370 as an indication of polymerization

   In discussions with the incident commander and the NTSB on scene, NS noted a 3°F increase in temperature for tank car OCPX80370 as an indication that polymerization was occurring.

2. SPSI and SRS to incident commander: 3:00 p.m. deadline

   The vent and burn was originally scheduled for 1:00 p.m. on February 6, 2 hours ahead of the 3:00 p.m. deadline described to the incident commander by SPSI and SRS.

3. Oxy Vinyls to NS and NS contractors (not the incident commander): conclusion that dangerous polymerization was not occurring

   Oxy Vinyls, which was providing support to NS and its contractors but was not in direct communication with the incident commander, concluded based on the same evidence and its own knowledge of VCM that dangerous polymerization was not occurring. Oxy Vinyls shared its conclusions with NS and NS’s contractors while on the scene; these conclusions were not communicated to the incident commander.

4. Oxy Vinyls to incident commander: no communication reported by the incident commander (not invited to the meetings, not present, no contact outside them)

   According to the incident commander, no Oxy Vinyls employees were invited to these meetings, and none were present. Nor did any Oxy Vinyls employees communicate with the incident commander outside these meetings.

The 3 °F increase the report attributes to NS matches the change computed from the table, 135 to 138 between 4:00 and 5:00 p.m. on February 5. The same table shows later readings at or below 138 apart from the fire-coincident 139.

The vent and burn time is consistent across the two dates: about 4:40 p.m. in the preliminary record, 4:37 p.m. for detonation in the final report.

ESI detonated the vent and burn charges at 4:37 p.m. for all five VCM tank cars, puncturing each tank car at two points: the highest point in the vapor space and the lowest point where the liquid had pooled.