I remembered reading about a catastrophic helmet squeeze and looked it up. Peter Keeble, in his book "Ordeal by Water" (Doubleday & Co. 1958. Pg. 160) describes such an event:
"We pulled the limp suit over the bulwarks and into the diving boat and dropped the horrifying bundle on the bottom boards. Somebody, with shaking hands, reached to unscrew the front glass of the helmet - and released a warm sickening flood. Hurriedly we threw a canvas engine cover over the pitiful, terrifying remains. One slip, and the accident we had lectured on, threatened about, painted ghastly pictures of and done our level best to guard against, had happened. Casually, the unfortunate shipwright had been allowed to drop forty feet and the instant change of depth and pressure had produced the giant squeeze. Most of the diver had been forced up into the copper dome of his helmet."
