It was August 10, 1963, and Paul Ramer and I were climbing in separate parties on the practice cliffs near Hidden Falls in Cascade Canyon. Ramer, standing on a talus slope about 200 feet below me, wore an aluminum hard hat, while my helmet was a mesh-reinforced fiberglass model.
As I bent to coil my rope, my helmet's loose chinstrap proved to be inadequate. The helmet rolled and fell toward Ramer's party, finally hitting Ramer in the head after a free bounce of about 30 feet. Only at the last moment did Ramer's party realize that my cries of "Rock!" were intended for them, and at no time did they see the helmet falling toward them. Ramer's helmet prevented all injury, and he continued climbing immediately after the accident.
Ramer certainly could have sustained some injury if he had not been helmeted. This incident supplies another straightforward argument for the use of hard hats by all rock climbers. The incident never would have occurred if I had been more attentive to the possibility of dropping an inadequately secured helmet.
Read the full report and analysis from Accidents in North American Mountaineering.