What type of explosion is characterized by a moderate pressure rise and subsonic velocities?

The correct answer is a nonseated explosion. This type of explosion is characterized by a moderate pressure rise and occurs at subsonic velocities, which means that the shock wave travels slower than the speed of sound. Nonseated explosions do not create the intense pressure and high-speed shock waves typical of seated explosions, which can lead to more destructive outcomes.

In nonseated explosions, the energy release is significant but not as powerful or rapid as that found in high order explosions. This category includes many common scenarios where combustible materials ignite and produce a controlled expansion, resulting in noticeable but not catastrophic effects. Understanding the dynamics of nonseated explosions is crucial for fire investigators, as it helps them assess the potential risks of materials involved in fire incidents and explosions.