to be the case. Keeping this requirement in mind is an essential ingredient in the quest for accident-free work. The past four or five decades have seen a great expansion of cryogenic technology. Cryogenic liquids, such as oxygen, nitrogen, hydrogen, and helium, have become commonly used in a number of different applications and are easily available in any part of the United States and, indeed, almost anywhere in the world. Not only are these liquids available, they have become less expensive and also available in ever larger quantities. As quantities increase, so also do the conse­ quences of mishaps. The future seems to hold promise of ever larger and more widespread use of the common cryogens. Thus, the importance of safety also increases as time progresses.