If LPG cylinders or their valves or fittings are damaged and gas leaks into your
boat's interior there is a risk of it being ignited and causing a fire or explosion.
To reduce the risk of this happening every cylinder (full or empty, stored or in
use) must be properly secured on open deck or in a suitable cylinder locker:

Either on decks, cabin tops or outside cockpits:

• They must either be stored on open deck, cabin tops or outside cockpits, as
  long as any leaking LPG can drain overboard.
• They must be at least 1m (3ft 3ins) away from hatches, other openings into
  the boat and possible sources of ignition.
• Cylinders, low pressure regulators and associated equipment can be
  enclosed in a shelter on open cabin tops or outside of cockpits, as long as
  any escaping gas can flow overboard and not into the confines of the boat.

Or, for cylinder lockers:

• Cylinders can be secured in a suitable cylinder locker, which must be gas
  tight to the height of the regulator and valve. To help keep the lockers gas
  tight they must be designed to only open from the top.
• Cylinder valves, regulators and other components in the lockers can be
  damaged if boating equipment, such as mooring pins, are thrown in. Damaged gas components could quickly leak, leading to a serious fire or
  explosion potentially. To minimise the risk of this happening cylinder lockers
  must have a lid or cover to protect the cylinders, low pressure regulators
  and associated equipment from mechanical damage.
• To prevent gas, which has escaped in the cylinder locker, from entering the
  interior of the boat LPG must be able to drain effectively from the lowest
  point of the cylinder locker to a point outside the hull, above the waterline.
  Boats manufactured before 3 January 2000, which have a cylinder locker
  drain as near as practical to the bottom of the cylinder locker, are exempt
  from this part of this Standard. [7.2]