The on-board hydrogen storage tanks are extremely strong, carbon-fiber wrapped tanks. Similar to CNG tanks, hydrogen tanks are put through a battery of extreme tests, including bonfire, pressure cycling, impact, burst and gunfire tests. The tanks must meet strict manufacturer guidelines and applicable DOT criteria for acceptable use on public roads. In addition, each tank is equipped with a thermally activated pressure relief device (PRD/TRD) that provides a controlled release of the tank contents if tank temperature, and therefore pressure, exceed allowable thresholds.