On February 11, 2018, about 1:15 p.m. a module of 25 horizontally mounted high-pressure gas cylinders loaded with 240 kilograms (kg) of compressed hydrogen, UN1049, caught fire while being transported. The incident occurred on Golden Springs Drive, near South Brea Canyon Road, in Diamond Bar, California. About 120 kg of the hydrogen was released from 12 of the cylinders that were exposed to the fire. The fire was extinguished, and the trailer was secured around 3:00 a.m. on February 12. No injuries were reported; however, about 500 persons within a 10-block business district were evacuated. Weather at the time of the incident was 69℉, maximum wind gusts were about 14 mph, there was no precipitation, and visibility was 10 miles.
The cylinders were manufactured under US Department of Transportation (DOT) Special Permit 14576. The cylinders were constructed of a carbon fiber composite wrap over an aluminum inner liner. About six weeks prior to the incident, a DOT-approved cylinder requalification facility, conducted a 5-year requalification inspection of the cylinder module. No exceptions with the cylinders or associated equipment were noted during the requalification inspection. However, preliminary inspection by NTSB investigators found: