49 CFR §831.2

1. (a)Aviation accidents as described in subpart B of this part;
2. (b)Highway accidents as described in subpart C of this part;
3. (c)Railroad, pipeline, and hazardous materials accidents as described in subpart D of this part; and
4. (d)Any accident that occurs in connection with the transportation of people or property that, in the judgment of the NTSB, is catastrophic, involves problems of a recurring nature or would otherwise carry out the intent of its authorizing statutes. This authority includes selected events involving the transportation of hazardous materials, including their release.