Set the gas flow rate to 15 liters/min and start the gas. In about 2 minutes the bag that is sitting above the head will be inflated with the gas. The gas will continue to flow, leaking out from around the elastic. You can use a mirror to check that it is correctly positioned.
For the next step, hypeventilate for one or two minutes. Then, fully exhale, expelling all the air from the lungs. Pull the bag down over the face until it is positioned around the neck, and take the deepest breath possible.
Within one or two breaths consciousness will be lost. The gas will continue to flow, all the while escaping from around the neck elastic and taking with it any exhaled carbon dioxide. Death occurs within 5 - 10 minutes. The gas will continue to flow, escaping into the room until the cylinder is empty.