PRELIMINARY REPORT

HAZARDOUS MATERIALS

Accident Performance of DOT-117R Tank Cars

Doon, Iowa

June 22, 2018

HMD18LR002

The information in this report is preliminary and will be either

supplemented or corrected during the course of the investigation.

On June 22, 2018, about 4:35 a.m. central daylight time, southbound BNSF Railway (BNSF) 

freight train U‐CPGSAP‐059 derailed 33 jacketed DOT‐117R tank cars at milepost 165.3 on the 

BNSF Marshall Subdivision in Doon, Lyon County, Iowa. The train was being operated in a 

distributed power configuration with 2 head-end locomotives, 2 head-end buffer cars, 98 tank cars, 

1 rear-end buffer car, and 1 trailing distributed power unit (DPU) locomotive loaded with about

2,426,325 gallons of UN1267 petroleum crude oil. Maximum authorized speed on the territory was 

49 mph. The Federal Railroad Administration (FRA) determined the train speed was about 48 mph 

when the train encountered the emergency brake application. A total of 10 tank cars were breached, 

releasing about 160,000 gallons of crude oil. The area received 5 to 7 inches of rain during the 

48 hours prior to the accident, washing out track and flooding a tributary of the Little Rock River and 

farm fields adjacent to the derailment location. (See figure 1.) Released crude oil reached the Little 

Rock River and prompted the evacuation of 18 to 20 people. No injuries were reported. A unified 

command consisting of BNSF, U.S. Environmental Protection Agency, Iowa Department of Natural 

Resources, and Lyon County, Iowa, was established to mitigate and recover the released crude oil.

ConocoPhillips Canada Marketing & Trading ULC originated the shipment from the 

Hardesty Terminal at Rosyth, Alberta, Canada, and its destination was the ConocoPhillips Company 

in Houston, Texas. The hazardous material released in this accident was identified as Surmont Mix 

A, a heavy crude oil and diluent mixture that exhibited an American Petroleum Institute (API) gravity 

of 19.9, initial boiling point of 115.0°F, flash point of -31°F, and vapor pressure of 4.7 psi. While 

these characteristics would have placed the material in Packing Group II (flash point less than 73°F 

and initial boiling point greater than 95°F), the shipper classified the material as Hazard Class 3, 

Packing Group I (highest degree of danger). 

On July 10, 2018, National Transportation Safety Board (NTSB) investigators completed 

on-scene work in Doon, Iowa, where tank car wreckage was staged after the accident. Additional 

investigative work to examine parts removed from one of the tank cars is planned at the NTSB 

laboratories in Washington D.C.
Figure 1. Accident scene. (Photo courtesy of BNSF Railway)

The derailed tank cars were originally specification DOT-111A100W1 that were built to the 

Association of American Railroads CPC-1232 industry standard for tank cars ordered after 

October 1, 2011, for use in crude oil and ethanol service. Each tank car had about 29,000 gallons 

capacity and was equipped with a jacket, insulation, and full-height headshields. From 2016 through 

2017, the tank cars were retrofitted to specification DOT-117R in accordance with Pipeline and 

Hazardous Materials Safety Administration (PHMSA) regulations, by replacing the bottom outlet 

valve operating handle with a disengaging mechanism designed to prevent unintended opening in 

accidents.1 Preliminary findings from the examination revealed breaching damage in 10, or about 

one-third, of the derailed tank cars. (See table 1.)

 1 Pipeline and Hazardous Materials Safety Administration final rule HM-251C, FAST Act Requirements for 

Flammable Liquids and Rail Tank Cars, Federal Register 81, no. 157 (August 15, 2016): 53935.
Table 1. Tank Car Breaching Damage.

Consist 

Line 

Number

Car 

Mark

Car

Number Breaching Damage

17 CTCX 716781 Circumferential shell tear separated the B end head and stub sill assembly from the 

car.

18 CTCX 716860 Bottom outlet valve handle was damaged, and the ball valve opened 2 1/4

in., draining the tank contents.

20 CTCX 717997 Circumferential shell tear separated the A end head and stub sill assembly 

from the car.

22 CTCX 716898 Puncture to the center right bottom tank shell measuring 1 ft. X 1 ft. 

Puncture in the A end right shell adjacent to the head measuring 3 ft. X 3 ft. 

23 CTCX 716624 Tear measuring 7.5 in. X 12 in. in the center-right top shell.

26 CTCX 717904 Tear measuring 2 ft. X 3 ft. to the B end center-right shell.

28 CTCX 716530 Puncture measuring 5 in. X 12 in. to the B end bottom head (through 

headshield).

29 CTCX 717805 Puncture measuring 36 in. X 29 in. to the B end center shell. 

32 CTCX 718011 Tear measuring 8 in. X 1 in. in the center top shell at top fittings pad-to-shell 

interface.

35 CTCX 717041 Puncture measuring 24 in. at A end top shell. 

Parties to the investigation include FRA, PHMSA, BNSF, The Greenbrier Companies, and 

Trinity Tank Car.