91. It is hereby declared that, in any proceedings in which it is in issue whether any relevant apparatus complied with the protection requirements or the requirements of regulation 30 above as the case may be at the time when it was supplied or taken into service as the case may be, a court may infer that such apparatus did not so comply at that time if—
(a)it is proved that it does not so comply or did not so comply at a time subsequent to its having been supplied or taken into service; and
(b)having regard to all the circumstances of the case, it appears to the court that the failure of the apparatus to comply at the time referred to in sub-paragraph (a) above is not attributable to any cause arising subsequent to its having been supplied or taken into service.