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Macdona, Texas

A tank car loaded with 90 tons of liquefied chlorine experienced a puncture, releasing about 60 tons of poisonous liquefied chlorine gas. The gas quickly vaporized and spread within 700 ft of the derailment site, drifting 10 miles northwest. This incident highlights the vulnerability of tank cars transporting poisonous gases and the need for prompt action and safety measures.

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Macdona, Texas

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  1. Macdona, Texas Hazardous Materials

  2. N Car #16 - Chlorine

  3. Chlorine Release • Tank car loaded with 90 tons of liquefied chlorine • About 60 tons of poisonous liquefied chlorine gas released • Immediately vaporized and engulfed derailment site within 700 ft • Drifted 10 miles northwest

  4. Chlorine Gas • Transported as a compressed liquefied gas • Poisonous by inhalation • IDLH - 10 ppm • EPA estimated concentration around 400,000 ppm

  5. Tank Shell Tank Head Puncture (2” x 11’) Weld Seam Frost Line

  6. Dent ##2 Outer Jacket Head Shell Dent #1 & puncture

  7. Punctured Tank Car • Manufactured in 1976 • Insulation & outer steel jacket • Tested to 500 psig • Tank Shell • ¾ inch thick • Non-normalized steel • Tank Heads • 13/16 inch thick • Hot formed steel

  8. Tank Car Performance • Tank head • DBTT < - 40 o F • Ductility limited puncture • Tank shell • DBTT > 85o F • Brittle under most operating conditions

  9. Tank Car Performance Cont’d • Charpy impact energies lower than some of the Minot tank cars • Fracture toughness of the steel from the Macdona tank car inferior to the steels from some of the Minot tank cars

  10. Conclusion The tank car shell involved in the Macdona accident would have been susceptible to catastrophic fracture if the shell had experienced a large penetration of several feet or more across the shell.

  11. Previous Recommendations Low fracture toughness of tank car steels Minot, North Dakota • Updated evaluation of FRA progress to implement safety recommendations • Reiteration of tank car safety recommendations

  12. Previous Recommendations Cont’d Vulnerability of tank cars transporting poisonous gases – Graniteville, SC • Recommendation to FRA to mandate operational measures (tank car placement and restricted speeds) • Prompt action required

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