"(1) While the hazard is increased by any means within the control or knowledge of the insured; or
"(2) While a described building, whether intended for occupancy by owner or tenant, is vacated or unoccupied beyond a period of 60 consecutive days; or
"(3) As a result of explosion or riot, unless fire ensues, and in that event for loss by fire only." [Formerly 743.624]