19.—(1) Subject to paragraph (2),
(a)an employer shall ensure that no person employed by him modifies at work the body of a transportable gas container–
(i)of seamless construction; or
(ii)which has contained acetylene;
(b)an employer shall ensure that no person employed by him modifies at work the body of any other type of transportable gas container if that modification would put the transportable gas container outside the scope of the design standard or design specification to which it was originally constructed;
(c)a person shall not supply any modified transportable gas container for use unless following such work a person or body of persons approved by the Executive for the purposes of regulation 16(2)(a)(i) has marked or certified it as being fit for use, or, in the case of an EEC-type cylinder, an inspection body referred to in regulation 16(2)(b)(i) has so marked or certified it.
(2) Paragraph (1) shall not apply to the remaking of a thread if this is done in accordance with a standard approved by the Executive.