Plastic bag & gas
Rather than combining drugs with the plastic bag, it is also possible to cause unconsciousness using gas. The method is to fill the bag with gas, so that rather than breathing in oxygen, the gas is inhaled instead. This does not interfere with the body's unconscious desire to breathe, but the gas inhaled has no oxygen.
Since the gas being breathed in has no oxygen, what is breathed out has no carbon dioxide. This combats the problem of breathing in air with high CO2 concentration where the body starts to get alarmed.
According to Nitschke & Stewart1, and the Alt Suicide Holiday website2, breathing in a gas with no oxygen content should render unconsciousness in a matter of seconds. Estimates for time to death with this method were not easy to find, although it would seem less than 10 minutes. 20 minutes of gas is said by Nitschke & Stewart to be more than enough to ensure death. Death should be relatively painless, although before being rendered unconscious there will be brief panic knowing that the body is not breathing in air. On discovery, the body will look like death was peaceful.
Tasteless, odourless and non irritating gasses are sensible for this method. Helium, argon and nitrogen all fulfil those requirements, and are readily available to purchase (helium especially).
The method works by running a pipe from the gas container into the bag, filling it with the gas, breathing out fully (important), then placing the bag, emptied of oxygen then filled with gas, around the head, ensuring the bag is sealed to the neck with elastic. The pipe from the gas container must keep flowing into the bag to ensure the gas concentrations are maintained, and a gas flow regulator can be helpful to ensure the gas flows in at a good rate.
A few deep breaths in and out are all that is required to cause unconsciousness (can be up to two minutes though), with death following in around 13 minutes, although can take up to 40 minutes. An 8.8 cubic feet tank of helium should be enough to achieve this, although a bigger 14.9 cubic feet tank better. It is possible to join up two smaller tanks but that adds complication and risk of failure.
It is probably also possible to use a small tent that can be sealed. Ideally pushing out all the air whilst inside it, making sure most air is pushed out before sealing the tent, then filling it up with helium, argon or nitrogen. However, this method might require using more gas, and does not seem to be discussed in suicide literature and forums as the preferred way of performing this method.
Nitschke & Stewart1 in the Peaceful Pill Handbook describe in great detail how to create a reliable "exit" bag to use with this method. They also discuss recommended gas flows into the bag, how much gas is required and how to regulate the gas flow, thus maximising the chances of swift unconsciousness and the gas lasting long enough to ensure death. Their forum also have numerous discussions on this subject. Helium flow control kits, and gauge & hose kits, are available for sale from the Peaceful Pill Handbook website under "Buy now".
Alt Suicide Holiday2 also have extensive information on this method, together with some reports from people who had difficulty using this method, and possible explanations on where they went wrong.
Whilst this method would seem highly effective, certain details must be done right otherwise brain damage is possible. It would be highly advisable for anyone considering this method to consult the videos and text in the Peaceful Pill Handbook first, and check the information on Alt Suicide Holiday.
It is important to be able to breathe freely for this method, as swift unconsciousness relies on taking deep breaths of the gas. Anyone with severe respiratory problems (e.g. emphysema or lung cancer) should not consider this method. Likewise, this method does require some preparation and co-ordination to carry out effectively. It may thus not suit someone who lacks manual dexterity or has no mobility.
This method causes swift unconsciousness so is not recommended for suicidal gestures. There is very little time for a change of mind.
Dangers of this method are permanent brain damage if it is interrupted before completion, as once the brain is starved of oxygen, brain damage starts to occur. It is therefore important that there is no chance of discovery whilst using this method.
Another vital factor is to ensure there is sufficient gas (see above) to ensure death, and that there is no chance of tearing/removing the bag over the head (or tent) whilst unconscious (which might happen if the bag is not fixed snugly and, say, if the attempt is carried out sitting, and unconsciousness results in falling off the chair and the bag becoming dislodged).
Anyone seriously considering this method of suicide is advised to read Help me first.
Alt Suicide Holiday website, http://ash2.wikkii.com/wiki/Helium, with their information taken from a range of sources but including Dr. Pieter V. Admiraal, Guide to a Humane Self-Chosen Death (2006).