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

Fault tree analysis techniques as applied to a patient monitoring system are discussed. This process provides mapping for test procedures to 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 process as applied to one product is explained. The fault tree for this instrument produced a total of 42 test procedures for final system test use. The time for tree and test generation was six man-weeks. The tests required two man weeks to complete. These tests were instrumental in finding 16% of the total defects and 36% of the critical defects for this product