Section 49B(4)(c) in The West Bengal Factories Rules, 1958
(c)All parts of an oven or drier which has undergone any alteration or repair which has the effect of modifying any of the design characteristics, shall not be used unless a thorough examination and test as have been mentioned in clause (b) has been carried out by a competent person and a certificate of such examination and test signed by that competent person has been obtained and is kept available for examination by an Inspector at all times during working of the factory.