Do practice this first, because you may be quite incapacitated when you try to do it, and the bag in particular should be prepared in advance.

This is a self-use bag is designed to allow the sufferer to end his or her life in dignity and in a peaceful way.

Essentially, the idea is to place a plastic bag over the head and draw a string tight enough to be airtight, allowing the person to quietly die from asphyxiation/oxygen deprivation.

Do practice this first, because you may be quite incapacitated when you try to do it.

If used without an inert gas, a carbon dioxide build-up will happen, which is unpleasant and will elicit a panic response. This can continue even into unconsciousness, and the bag may be ripped off, causing failure and further stress. Using an inert gas prevents CO2 building up and allows one to die of oxygen deprivation. (and with oxygen deprivation, you will indeed see the white light, so just walk towards it - yes really)

Helium is perfect, as it's obtainable at any party supply shop, plus the properties of helium make it easy to use.

It is preferable to take the decision to end one's life before getting to the stage of needing assistance, because anyone assisting you can, and on current evidence will, be prosecuted by the law of the land. Also, since exit bags are not readily available for purchase, where do you get one?

Strangely enough, the ideal bag for a DIY exit bag is probably already in your home - a tie-top rubbish bag.

The only other thing that is needed is a short length of flexible hose - one which will fit the nozzle of the helium tank.

First of all, fold the top of the rubbish bag twice to ensure no gaps are left at the bottom of the bag.

Then make a connection for the hose, using parcel tape or masking tape. There is no issue of pressure, as the bag is never under more than air pressure.

When needed, the helium is attached to the hose, then the bag fitted over the head and tied tight. As this is not necessarily an easy thing to do, simple practice is sensible.

Expel as much breath as possible before fitting the bag, and start filling with helium immediately. You won't even know you're breathing helium - the human body ignores it, and the person will feel pretty much like they're breathing in ordinary air. (Helium is used by deep divers who must have oxygen without CO2, although they do have oxygen mixed with theirs!)

Once the bag is filled, but not under pressure, turn the helium off and keep breathing normally.

The ideal position is reclined in a comfortable place, but there are a couple of other issues that need to be dealt with.

Dying can be a messy business and it is quite normal for people to void their bladder and/or bowels immediately after death. This isn't nice for loved ones to deal with, so some sensible precautions are advised.

If adult diapers are not available, make use of towels and plastic sheeting as needed to ensure no mess is left on the bed/couch.

If it is too late to do without assistance, and do need some small amount of help, there are a couple of ways helpers can be made safe from prosecution.

Making sure any helper wears a pair of gloves and then wraps YOUR hands around any items touched. No doctor/pathologist or coroner is going to be able to deliver any verdict other than suicide then. Writing a short letter is also good evidence to present to the coroner.

Rightly or wrongly, the police have shown a determination to prosecute those who assist in suicide, which is the legal status of euthanasia in New Zealand and the courts have shown that they indeed issue prison sentences for the "crime".