It's a sort of "death pod". One gets inside of it, and it then supplies nitrogen gas. It kills by suffocation, because it isn't oxygen. The pod has windows, so that its user can see outside of it. So one can die as one watches some outdoor scenery, like a sunset.
Other gases could work, especially noble gases. I know of someone who committed suicide by breathing helium. He researched various ways of dying and he decided that breathing helium was the most pleasant way to go.
The air you're breathing is already mostly nitrogen; it won't kill you. What such a hood does is slowly change the proportion of nitrogen to oxygen in your breathing space, until there isn't enough oxygen present to maintain normal functions, especially those of your brain. Your brain absolutely relies on oxygen for most of its processes, since it is the catalyst for the creation of glucose, the chemical that supplies the rest of your brain with energy and therefore is necessary for any sort of neural activity. This is so critical that more than a fifth of your overall oxygen intake is devoted to keeping your brain running.
Brain damage runs ahead of perception, as always. Cell death begins almost immediately in an anoxic space, becoming irreversible after about a minute as neurons themselves stop functioning. Low-oxygen environments will take longer, but it is still a frighteningly swift process. Disablement is easier to accomplish than death, as you tend to instinctively panic and do things like (for instance) panic and get out of your death pod. Hence helium and xanax and etcetera to belay this response, though I would be surprised if either work 100% -- brains are both resilient and adaptive, and those panic feelings serve a purpose- your brain will produce them if it can, even if it has to jerry-rig the entire system to do it.
In any case, you might be able to save your life at thst point, but cell death is cell death. If you've lost a piece of your neural lattice, you've lost a part of your body function, and a change in something like your personality or ability to communicate is almost certain. Your brain, in crisis mode, tries to preserve core functions, but it does so at the cost of your prefrontal cortex where all of those nice fancy higher brain functions partially reside. So I suspect any attempt at suicide by these means will be successful if serious, at least in a sense. The body might survive, but "you" will not. The brain will have to rebuild itself, but it won't do it in the same shape.
Five minutes? You're probably dead, unless you're a seasoned deep seadiver or US Marine or something. Even the most fervent efforts of your brain to keep its basic processes going can't work if glucose production is hindered for long enough. Your brain enters a state akin to a seizure, an aimless electrical storm; your organs stop working, and one by one your various life functions cease. The process does not take long, and you almost certainly won't survive. CPR can restart a heart, but it cannot rebuild a fatally compromised neural network.
Jack Kevorkian
