I am surprised of the cause that you state. If I recall, the automatic brake handle was in the running position as was the independent brake handle. On any account an emergency brake application should have tripped the PC valve taking the unit out of dynamic braking. No one wants to admit it, but it was quite possible that the crew went to sleep. I had a dynamic failure in tunnel six with a three unit lite helper consist returning to SLO, and it was very obvious in a few seconds. Air brakes were immediately applied and used all the way down the grade. The accident took place in the middle of the night and the crew had quite a wait at the Cuesta siding for a Westbound train. The clerk had often taken rides on helpers and was going to transfer to engine service in Bakersfield the following week. The 8642 was destroyed and one of the trailing Uboats had a broken frame. The two trailing Geeps stayed upright although at least one of them went on its side during cleanup. The accident took place just railroad east of tunnel seven, and there were scrape marks at the east end of tunnel seven showing that the derailment had started in that tunnel. Turnover speed at the sight was sixty-six mph, and the damage indicated that the speed was in excess of that speed.