(5)In the case of gasholder of which any lift has been in use for more than two years, the internal state of the sheeting shall, within one year of the coming into Operation of these rules and thereafter at least every period of four years, be examined by a competent person by means of electronic or other accurate devices :Provided that if the Chief Inspector is satisfied that such electronic or other accurate devices are not available, he may permit the cutting of samples from the crown and the sides of the holder :Provided further that if the above inspection raises a doubt, an internal visual examination shall be made.
