Wireless sensor networks (WSNs) have been used to observe and monitor many environments for specific purposes and in many ways over the past few years. A number of operational trade-offs are possible when planning a WSN, influencing coverage, bandwidth, redundancy, lifetime, expandability, and so on. However, for systems in potentially hazardous locations or those experiencing restricted access, system unreliability tends to be the greatest operational concern. In the process of creating reliable WSNs for hazardous locations, it is highly desirable to ensure both an accurate and a reliable system design prior to deployment, and with as little unnecessary trade-off as possible. Especially as sensing systems become larger and more complex, and potential failure modes increase, this becomes more difficult to achieve. In an attempt to answer the question of reliability assurance, the authors investigate WSNs in the context of accurate and fast modelling of such networks. A comprehensive comparison of three modelling tools (ns-2, OPNET, and OMNeT++) is explored in this chapter, concluding that OMNeT++ is worthy of study as an alternative to the other two more established tools. As an illustration of the use of OMNeT++, two modelling schemes are simulated and compared against the theory to determine both bit-level correctness, but also to demonstrate ease of modelling and analysis.