Once, I had occasion to yell “Fire” in a crowded theater. I was on crutches at the time, and at a reception after an opening-night performance of “The Dybbuk.” While leaning against a wall and eating a smoked-salmon canapé, I felt heat on my lower back. Smelling smoke, I craned my head to see a small candle igniting my shirt, and flames licking their way up toward my collar. The reactions around me were diverse and instructive. A woman shrieked, and a man laughed. But neither did anything. I picked up my crutches, hobbled to the open bar and asked them to douse me. Incredibly, the barmaid started by daintily pressing ice cubes against the flames, until I suggested that she just drench me with the contents of her bucket.

What surprises me, in retrospect, about the incident is the curious range of reactions it provoked — the same range that is the subject of Amanda Ripley’s new book on human response to disaster, “Unthinkable” (Crown, 288 pages, $24.95). The reactions started with paralysis, from immobile fear to unhelpful guffawing, then progressed to bizarre and irrational attempts to help. And my own reaction was no more appropriate. A lifetime of hearing “stop, drop, and roll” proved useless: The three words that might have saved my skin, had the fire been worse, did not even occur to me until hours after. I think I might have even said “please” when I asked for the ice bucket.

Ms. Ripley’s book traces the reactions to many catastrophes — a litany of disasters, mass deaths, and heroic acts familiar to anyone interested in the human experience of extreme duress — and finds similarly staggering deficits of common sense, as well as moments of real courage. The evacuation of the World Trade Center, which she narrates through the testimony of Elia Zedeño, a Cuban-American who worked on the 73rd floor of Tower 1, was delayed by disbelief, by hushed chattering about what to do next, and then by high-heeled shoes piled in the stairwells, discarded mid-evacuation by women who had underestimated their peril and overestimated their mobility. In another case, the Air France crash in Toronto that set a whole plane ablaze but killed not a single person, the competence and insistence of a well-trained flight crew saved lives. Amid all the chaos and irrationality, Ms. Ripley says more than once, the disaster victims tend to observe surprising levels of decorum, often behaving even more politely than they would have in calmer times.

Broadly speaking, though, this decorum is itself a form of dysfunction, and what they tend not to do is act sensibly. Just as we misjudge the probability of catastrophes ahead of time (either by thinking imminent disaster “can’t happen to me,” or by thinking highly unlikely events are worth worrying about), disaster victims immediately neglect what they know about staying safe. They forget the mantras of safety, no matter how familiar; “stop, drop, and roll” is the least of them. Evacuating burning planes, passengers routinely defy the safety briefings by trying to bring bulky carry-on items with them, even as the cabin fills with noxious black smoke. They run in the direction of fire trucks — and fires — rather than away from them. When flight instruments fail, pilots get frantic, disregard thousands of hours of training, and fly hundreds of passengers to their death. No matter how many times they have been told procedures, people become bad listeners at the critical moment.

Except when they don’t. This is a book rife with contradictions, few if any of them the author’s fault. After giving countless intriguing examples of panic and paralysis in disaster situations, Ms. Ripley lauds security professionals for saving lives by conducting the same safety drills she says most people forget during moments of panic. And she points out others who survive horrific disasters in part because they did pay attention to in-flight safety instruction cards. There is no inherent contradiction in pointing out that properly conducted drills work, but neither is there a clear lesson in showing deadly paralysis in one catastrophic situation and heroic action in another. Nearly every lesson learned from every disaster seems to be contradicted by another person, or another disaster. Some say the reasons are genetic or hormonal — Ms. Ripley suggests that paralytic fear in dangerous situations is a version of “playing dead” — but even the scientists don’t really know for sure. They have outlines of a psychological profile of resilience (it helps to be a cocky, physically fit male), but those outlines are at best vague.

This is, as I say, not really her fault: Humans react differently in different situations, and the muddledness of her account of the science of disaster response seems to reflect the muddledness of the science of disaster response itself. But in a book that purports to say “who survives — and why,” one has a right to expect more answers than questions. Ms. Ripley’s book, although filled with amusing anecdotes, leaves no impression of what ultimately goes through people’s minds, except that almost every response to disaster is normal, even the responses that seem bizarre in the extreme. When facing death, people often show oddly skewed priorities. I’m reminded of a Belgian family who faced a torturously slow private disaster — death by thirst in the Sahara. After she mercy-killed her own husband and whimpering son, the mother wrote in her journal that their holiday had been worth it, and she regretted only that she was going to miss “Rambo III.”

Mr. Wood is a staff editor at the Atlantic.