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If, after testing your Helium cylinder and finding no oxygen contamination, a small Balloon Time cylinder (see Fig 5.5b below) will contain sufficient helium for a peaceful death, as long as the Exit gas flow control is used to establish the stated optimal flow rate of ~ 15 l/min.
The larger 420 litre Balloon Time cylinder will give a greater margin for error as this cylinder produces a usable stream of gas for approximately 20 minutes. This is more than enough time for a peaceful death to occur. Useful flow rates are obtained from either cylinder (>5 litres/min for 15 minutes with the small cylinder, and 25 minutes with the larger - see Fig 5.9).
Gas Flow Control
No matter which brand of helium gas is used, a flow rate of ~ 15 l/min is needed to prevent the accumulation of CO2 in the Exit bag. Exit has investigated several methods of controlling gas flow.
• For high pressure cylinders of nitrogen (Max Dog or equivalent) or helium, regulation is essential. Flow regulators are provided with the Max Dog system or can be purchased from gas providers. The Max Dog regulator shown in Fig 5.4 gives the pressure of nitrogen in the cylinder, and allows the output flow rate to be set at 15 litres/ min. Using this regulator, flow rate is constant throughout the hypoxic death.
• For ‘Balloon Time’ and similar helium cylinders at pressures of 1.7MPa, Exit has designed gas flow control fittings expressly for this purpose (Figs 5.10 & 5.11). These fittings give an initial flow rate of ~20 litres/min when the tap is opened fully. Exit helium flow fittings are available at: http://bit.ly/1ILmCMM