When a building, the use of which does not conform to the provisions of the zoning ordinance, is damaged by fire, explosion, act of God or the public enemy to the extent of more than sixty percent (60%) of its reasonable value, it shall not be restored except in conformity with the regulations of the district in which the building is located, provided that it may be restored if the Board of Adjustment finds some compelling public necessity requiring the continuance of the non-conforming use and the primary purpose of continuing the non-conforming use is not to continue a monopoly.