A Semiscale Mod-1 blowdown heat transfer test was conducted to supply thermal-hydraulic data concerning the fluid phenomena that occur during a small break loss-of-coolant accident. While it is easily recognized that a large break suddenly releases a great volume of coolant with rapidly falling levels and pressures, emergency core injection will also occur very early, compared to a small break. There has been concern that the longer times involved in small breaks (much longer subcooled flow periods) could lead to effects worse than for large breaks. Within the scope of the testing conducted, the small break has proven to be of lower consequences than the large break.