Safety-critical software-intensive systems of systems require rigorous verification and validation to ensure that they function as per requirements. Unlike verification, validation is typically an ill-defined activity for software development. This paper presents a well-defined validation metrics framework which uses hazard analysis, and the derived software requirements for mitigating the identified hazards, as proxies in gauging the sufficiency of the software safety requirements early in the software development process. Moreover, traditional hazard analysis techniques are insufficient to deal with the complexity and size of systems of systems. This paper examines the nature and types of hazards associated with systems of systems and presents a new technique for analyzing one type of emergent hazard known as an interface hazard.