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GAS SUPPLIES AND GAS DISTRIBUTION SYSTEM back of the welding flame into the cylinder. The signs of decomposition are: – The temperature of the cylinder shell rises, starting at the area within which the decomposition commenced.

– The cylinder pressure increases (only evident when the cylinder is in use and a regulator with gauges is fitted on the top valve). – If, after a complete flash-back, the gas released from the top valve contains soot, and has an unusual smell.

On suspicion that decomposition may have started in the cylinder, shut the top valve immediately, and remove regulator or other fittings attached to it. The cylinder must be checked for increase in temperature by repeatedly feeling the cylinder shell all over by hand.

If temperature of the shell rises, but has not exceeded hand-heat (about 50°C) the cylinder must be taken to the railing immediately and thrown over board. The cylinder must be cooled by copius amounts of water while it is being moved. If the ship is in port, hang the cylinder by a rope into the sea and call the fire brigade. It is possible to stop a decomposition by keeping the top valve closed and cooling the cylinder with large quantities of cold water, but if this is to succeed it must be commenced at the latest five minutes after the decomposition has started, and must continue until the cylinder remains cold. However, out of consideration for the crew and the ship, do not try to save the cylinder but throw it over board as quickly as possible.

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If decomposition has reached a point where the cylinder can no

longer be touched by the bare hand (more than about 50 °C), the danger of an explosion is imminent and the cylinder must not be moved. Start cooling the cylinder immediately with large amounts of cold water from a protected position. All personnel not taking part in this operation must be evacuated from the area. When the cylinder has been cooled until the water no longer steams from the shell, it can be moved to the railing and thrown over board. Remember that cooling must be continued without interruption throughout the removal operation.

WARNING: The top valve of a cylinder containing decomposing Acetylene must be kept shut at all times!

Fatal mistakes have been made in cases of this kind; even experienced welders have opened the cylinder valve fully, in the mistaken belief that this would release the pressure in the cylinder. In fact, the opposite happens. The Acetylene that evaporates out of the Acetone passes the decomposition zone on its way to the top valve, decomposition becomes explosive and the pressure in the cylinder increases much faster than it can be released, with the result that the cylinder may explode within seconds.

Inhalation hazards

Acetylene is a non-toxic but mildly anesthetic gas. Formerly pure Acetylene was combined with Oxygen and used as an anesthetic in hospitals. There is a risk of asphyxia when the Acetylene level in respiratory air reduces the Oxygen content to three-fourths or less of