Recently I wrote about the state of Oklahoma's decision to switch from lethal injection to nitrogen asphyxiation. Although death penalty opponents (1) objected on grounds that this method was untested and could be a cruel method of execution, I noted that asphyxiation itself may not be cruel depending on the gas that was chosen. Nitrogen is an inert gas (2) that, when present at a sufficient concentration to displace oxygen, will a produce A rapid, painless death.
The mysterious death of four members of the Sharp family from Creston, Iowa, who were vacationing in Tulum in Mexico shocked both countries because of the strange nature of the death. The family went to sleep and didn't wake up. The only rational explanation for such a death was suffocation. But what could cause a family to die in this way?
In other parts of the world, the reason for this type of tragic accident is almost always carbon monoxide from a faulty furnace. But this explanation does not fit the circumstances in Mexico. The nighttime temperatures in Tulum, which is located on the Yucatan Peninsula, during the few days prior to the deaths ranged from 67-73°F, so it is unlikely that carbon monoxide, which is toxic, from a furnace was the culprit.
Since investigators were investigating the connections to the stove in the condo, the culprit was far more likely to be natural gas, but, as news outlet have been reporting, natural gas, which is primarily methane, is not toxic. When it kills it does so just like nitrogen, by depriving the brain of oxygen. Unlike nitrogen, methane is not inert, it reacts violently with oxygen, and can be detonated, when present in sufficient concentration, but a spark or even static electricity.
Not only is natural gas non-toxic, but it is also odorless. For this reason, a very small amount of t-butyl mercaptan, which smells like a combination skunk and rotten eggs, is added as an odorant. This is why you detect an unpleasant odor when the stove doesn't light immediately. Without the odorant, natural gas leaks would be very deadly, not because it is toxic, but because it can either explode or asphyxiate.
The only thing that is a bit puzzling about the Mexico deaths is that the odor didn't wake anyone up, but if sufficient quantities of the gas displaced oxygen quickly then the family would have been unconscious rather than asleep.
If the evidence finally supports natural gas as the cause of the accident then the press will have been wrong, as it is so often. Methane is not at all toxic. It is the lack of oxygen to the brain which can kill very quickly.
(1) My opinion on the death penalty is irrelevant and will remain my own. These writings concern only the science and pharmacology of capital punishment.
(2) An inert gas is one that is chemically unreactive. All inert gases are non-toxic. Chemically reactive gases may or may not be toxic.