Verification and validation of software in the field of scientific computing is increasingly being recognized as a critical part of the software, algorithm, and model development cycle. Multi-mechanics coupling represents an important and challenging role in providing confidence in the integrated multi-mechanics codes. This paper presents an overview of the math models implemented within the Sandia National Laboratories Advanced Simulation and Computing SIERRA Mechanics code project that supports the engulfed object-in-a-fire scenario. This scenario is characterized by coupling turbulent fluid mechanics, combustion, soot generation and transport, participating media radiation (PMR), thermal conduction and in the case of propellant fires, reacting Lagrangian particles. Attaining an adequate state of code verification for such a complex engineering mechanics scenario represents a daunting challenge. A systematic approach is therefore required. Examples of single and multiple mechanics verification methodologies will be presented.