(a) If the dwelling unit or premises are damaged or destroyed by fire or other casualty to an extent that enjoyment of the dwelling unit is substantially impaired, the tenant, unless such damage or destruction is caused by the tenant’s negligence or wilful act, shall not be liable to pay rent for such period of time as such impairment continues. In such case, the tenant may (1) immediately vacate the premises and notify the landlord in writing within fourteen days thereafter of his intention to terminate the rental agreement, in which case the rental agreement shall terminate as of the date of vacating; or (2) if continued occupancy is lawful, vacate any part of the dwelling unit rendered unusable by the fire or other casualty, in which case the tenant’s liability for use and occupancy shall be reduced in proportion to the diminution in the fair rental value of the dwelling unit.

(b) If the rental agreement is terminated, the landlord shall return all security and prepaid rent recoverable under section 47a-21. Accounting for rent, in the event of termination or apportionment, shall be made as of the date of the fire or other casualty.