Traces of Liquid Nitrogen
Posted by Karl Withakay on October 21, 2009
Tonight’s episode of NCIS, “Code of Conduct” featured the murder of a US Marine by ingestion of liquid nitrogen (LN2). We are told by the forensic pathologist, Dr. Donald “Ducky” Mallard, played by David McCallum (fans of classic TV may know him better as Illya Kuryakin in The Man From Uncle) that the Marine “…ingested enough nitrogen to freeze his internal organs, but technically that was not the cause of death.” The Assistant medical examiner tells us that the cause of death was actually breathing, “The nitrogen gas entered his lungs, essentially suffocating him.” Ducky also tells us that the victim lived on for several minutes after ingestion of the liquid nitrogen, and that “single gulp” was all that was necessary to kill the Marine.
It’s late, and although it would be an interesting and relatively easy exercise in math & chemistry I haven’t used since college (specific heat capacities, heat of vaporization of N2, heat of fusion of water, etc) to determine how much liquid nitrogen would be needed to freeze a human’s internal organs, I don’t feel like taking the time do it now. Maybe I’ll do it before watching Mythbusters tomorrow.
What I do want to first address is the claim that the victim was asphyxiated when the nitrogen gas (produced when the liquid nitrogen in his stomach boiled) entered his lungs. I’m not a doctor, but I see a few things wrong with this concept. Problem one is that the stomach does not really have a direct connecting pathway to the lungs. I suppose you could argue that he essentially burped up so much nitrogen from his stomach, that it displaced the air around his nose and mouth so that he was only able to breathe nitrogen. However, I’m thinking that his throat would have likely been frozen shut by the liquid nitrogen and that he would have choked to death instead. It might also be possible for his carotid artery to have frozen shut and for him to have essentially died of a stroke. I could be mistaken on htese points, and I’m hoping my friend Scott will chime in with a comment or two on this.
Also, several references were made in the episode to “traces of liquid nitrogen” being found or detected. At atmospheric pressure and temperatures above 37K (-196C) nitrogen is a gas, and would not generally leave “traces” behind that would indicate that LN2 had previously been present.
Finally, it is claimed that the LN2 was stored in a lunchbox thermos, and it is implied that the victim may have drank the contents of the thermos on his own (rather than being forced to drink it) because he was caught unaware by the contents of the thermos. I cry BS raise my eyebrow on both of these ideas. I doubt that a lunchbox thermos would contain any LN2 for long enough to be used in this way. Without a pressure relief valve, there’s a good chance it would pop its top off in less than a few hours. I also doubt that the thermos wouldn’t have been cold enough for the victim to notice something was fishy; it’s a thermos, not a laboratory grade vacuum flask.