They actually did say that the webbing of
the seat belt broke.
"A seat-belt failure as a result of improperly installed belts was used as a contributing factor to Earnhardt's fatal crash. That is according to Dr. James Hr. Raddin, Jr., M.D., the director of Biodynamic Research Corporation in San Antonio, Texas; and Dean L. Sicking, Ph.D., P.E., director, Midwest Roadside Safety Facility, professor of Civil Engineering, University of Nebraska.
Also participating in the investigation were James V. Benedict, M.D., Ph.D. for Biodynamic and John H. Reid, Ph.D. for the University of Nebraska.
The seat belt failure was termed "dumping" during the accident. This meant the adjuster mechanism became cockeyed (the lower end moved forward) and the webbing in the left side adjuster mechanism bunched up toward the lower end of the mechanism.
Belt webbing works best when it remains flat and all of its fibers are pulled at once. When a belt dumps, a greater stress is placed on fewer fibers, and there is a greater risk of tearing. The concept is similar to a heavy sheet of paper. It is difficult to separate the sheet if both ends are pulled straight. But if the paper is pulled on one side only and rips across, it will tear quickly."