Section 180(2)(v) in The Calcutta Municipal Corporation Act, 1980
(v)when, on an application made in writing by the owner or the person liable to pay its consolidated rate, it is established that during the period of the annual valuation remaining in force its value has been reduced by reason of any substantial demolition or has suffered depreciation from any accident or any calamity proved to the satisfaction of the Municipal Commissioner to have been beyond the control of such owner or such person; or