Special Investigation Report

Mobile Acetylene Trailer Accidents: Fire During Unloading in Dallas, Texas, July 25, 2007; Fire During Unloading in The Woodlands, Texas, August 7, 2007; and Overturn and Fire in East New Orleans, Louisiana, October 20, 2007

NTSB Number: SIR-09-01
NTIS Number: PB2009-917002

Executive Summary: The National Transportation Safety Board investigated three accidents that involved highway vehicles transporting bulk quantities of acetylene gas that occurred between July 25 and October 20, 2007, and reviewed reports of a 2008 overturn accident of another vehicle. The vehicles, called mobile acetylene trailers, carried up to 225 cylinders that were connected by a manifold system1 and filled with acetylene. Two of the accidents occurred as the vehicles overturned on public highways, in East New Orleans, Louisiana, on October 20, 2007, and in Lamar, Colorado, on June 9, 2008. Two of the accidents occurred while the vehicles were being prepared for unloading, in Dallas, Texas, on July 25, 2007, and in The Woodlands, Texas, on August 7, 2007. In the two overturn accidents, cylinders were ejected from the trailers and damaged, releasing acetylene, which ignited. In one unloading accident, the fire on the initial trailer spread to cylinders on an adjacent trailer; in the other, the fire spread to cylinders on adjacent trailers and to nearby buildings and vehicles. The failures of the cylinders on these mobile acetylene trailers and the resultant damage raised concerns about the accident protection provided by these vehicles, the adequacy of the minimum safety standards and procedures applicable to unloading these vehicles, and the adequacy of fire suppression systems at loading and unloading facilities. To address these concerns, the Safety Board conducted a special investigation of mobile acetylene trailers.

These trailers, with multiple cylinders and a manifold system for loading and unloading the cylinders, are the only vehicles authorized to transport and deliver bulk quantities of acetylene. Currently, two companies in the United States operate mobile acetylene trailers. Each company has about 200 trailers, thus the total number of these trailers is about 400.

The trailers in the four accidents that the Safety Board investigated and reviewed were operated by Western International Gas & Cylinders, Inc. (Western). In the 10 years before these four accidents, Western mobile acetylene trailers had been involved in additional accidents; the company investigated four of them. The Safety Board reviewed reports of three of these accidents that had some relevance to the accidents in this investigation.

In its investigation, the Safety Board attempted to determine the hazards of the transportation and delivery of acetylene gas in bulk. The investigation looked at the protection of the cylinders during a vehicle overturn and the standards and procedures for handling acetylene during loading and unloading. The following safety issues were identified in this special investigation:

As a result of this special investigation, the Safety Board makes recommendations to the Pipeline and Hazardous Materials Safety Administration and the Compressed Gas Association.


1. A manifold system collects the acetylene gas from multiple cylinders into one pipe or chamber; when the cylinders are filled, the acetylene gas is dispersed from one pipe to multiple cylinders.