Software safety goal verification using fault tree techniques: a critically ill patient monitor example

A systematic form of software safety goal verification using fault tree techniques is presented and applied to a patient monitor. The process provides: mapping out test procedures for stated safety goals; a concise archive of the safety subset of the product test documentation; and hazard avoidance verification as indicated by a preliminary hazard analysis. The fault tree for the monitor produced a total of 42 test procedures for final system test use. The time for tree and test generation was six man weeks, and the tests required two man weeks to complete. The tests were instrumental in finding 16% of the total defects and 36% of the critical defects for this product