The concept of safe fail is that safety shall be retained even if parts of the system or perhaps the whole system fails. As can be seen in Appendix A, there are many concepts in engineering safety for which the principle may be applicable. Sometimes in the literature, safe fail is put in contrast to fail-safe—a safe fail system, then, is a system designed to safely fail whereas a fail-safe system is one designed not to fail. (Put differently, it is safe from failing rather than safe when failing.) The point is somewhat polemical but, rightly used, an instructive one.