In this Part—

• “gas” means any substance which is in a gaseous state at a temperature of 15°C and a pressure of 1013.25 millibars and—

  1. a

     consists wholly or mainly of methane, ethane, propane, butane, hydrogen or carbon monoxide; or

  2. b

     is specified in an order made by the Department; or

  3. c

     consists wholly or mainly of—

     1. i

        a mixture of two or more substances falling within paragraph (a) or (b); or

     2. ii

        a combustible mixture of one or more such substances and air.

• “in”, in a context referring to a pipe-line or a length thereof or works or operations in land, includes a reference to a pipe-line, length, works or operations under, over, across, along or upon it;

• “owner”

  1. a

     in relation to any land, means a person, other than a mortgagee not in possession, who is for the time being entitled to dispose of the fee simple of the land, whether in possession or in reversion, and includes also a person holding or entitled to the rents and profits of the land under a lease or agreement the unexpired term of which exceeds 3 years;

  2. b

     in relation to a pipe-line, means the person in whom the pipe-line is vested;

  3. c

     in relation to a structure, means a person who, in relation to land being the site of the structure, is an owner thereof by virtue of paragraph (a) of this definition.