The difficulties to assess reliability of systems that use COTS components are sometimes compounded by the inaccessibility of some COTS codes. This paper develops an approach of Perturbation of Interface Parameters (PIP) to simulate failures of COTS components. It is to validate the use of PIP as a fault-injection technique to test COTS components and surrounding systems. Tests of a nuclear protection system will be presented to demonstrate that PIP can be used to assess and aid safety designs in COTS based software.