Gas cylinders are designed to be stored and operated in an upright position
with their 'on cylinder' valve uppermost. To help prevent damage and leaks they
must only be kept and used in this way.

If cylinders and their associated pipework and fittings can move about too
much, those fittings, valves or regulators can quickly become damaged and
leak. To reduce the risk of this happening, cylinders and their lockers must be
securely stowed.

It's recommended that cylinders, cylinder lockers or cylinder housings do not
obstruct people moving around the deck or walkway, or interfere with the
normal and safe operation of your boat.

Cylinders are designed to release excess pressure that can build up if they're
exposed to extreme heat. Under these circumstances, gas can quickly find its
way into the interior of your boat presenting a significant and immediate risk of
fire or explosion. To minimise the risk of this happening cylinders, cylinder
lockers or cylinder housings must not be located near to heat sources.
In the event of a fire on board, which causes the cylinders to overheat, an
explosion could occur or the cylinder could jet gas onto a fire, causing it to
escalate. To give you, or the emergency services, a chance to get to the
cylinders to remove them they must be readily accessible and movable. [7.3]

For existing boats, cylinders can be stowed on brackets or shelves fixed to the outside face of the transom but this is not recommended best safety practice. In these circumstances the cylinders, regulators and associated pipework have to be protected from damage in the event of collision, and be ventilated to allow any escaping gas to flow directly overboard. [7.3]