The Road Vehicles (Authorisation of Special Types) (General) Order 2003

10.—(1) Every gas propulsion system must be so designed and constructed that—

(a) the supply of gas to the engine is stopped by an automatic valve when—

(i) the engine is not running at all;

(ii) the engine is not running on the supply of gas; or

(iii) the engine ignition is off;

(b) where the valve mentioned in paragraph (a) is not integral with the regulator, it must be positioned upstream of the regulator so as to be able to isolate the gas container and filling point; and

(c) in the event of a rapid deceleration of the vehicle in an accident or similar occurrence, the supply of gas to the engine is automatically stopped at a point as close as is possible to the gas container and may only be restored manually.

(2) Where the engine or vehicle is constructed or adapted to run on one or more fuels as an alternative to gas or in addition to gas, the safety of the engine or the gas fuel system must not be impaired by the presence of any other fuel system.

(3) Except as stated in sub-paragraph (4), every gas container must (in addition to the isolation valve required under paragraph 5 and the pressure relief device required under paragraph 6) be fitted with an automatically-operated valve to prevent gas escaping from the gas container in the event of a fracture or failure of the pipeline or of any component in the gas supply system.

(4) In the case of a group of gas containers interconnected in such a manner that the pipework is protected in the event of an accident, the group of gas containers may be fitted with a single automatically-operated valve or device to prevent gas escaping from the group of gas containers in the event of a fracture or failure of the pipeline or of any component in the gas supply system.

(5) Any electrically operated valve must be constructed so as to open when electrical power is applied and close when electrical power is removed.

(6) Where the vehicle is equipped to operate at any one time on one only of two or more alternative fuels, a fuel selection system that complies with sub-paragraph (7) must be installed.

(7) A fuel selection system complies with this sub-paragraph if—

(a) it has a control switch that is readily accessible to the driver at all times and is clearly marked for the selection of each fuel;

(b) it has a change-over system, operated by the control switch mentioned in paragraph (a), which prevents the use at the same time of more than one of the alternative fuels, apart from where fuel remains in the common system during a change-over between alternatives; and

(c) it does not impair the safety of the engine or the fuel system.

(8) All the parts of every valve or cock which are in contact with gas must be made of suitable metal; but they may contain non-metal washers and seals if those washers and seals are supported and constrained by metal components.