Seat damage can often occur when a valve is first lifted as part of the general plant commissioning procedure, because very often, dirt and debris are present in the system. To ensure that foreign matter does not pass through the valve, the system should be flushed out before the safety valve is installed and the valve must be mounted where dirt, scale and debris cannot collect. Feel free to verify this act by going to any of the major valve manufacturer websites such as Spirax Sarco or Kunkle. As I stated in a previous post, steam hammering is a very common occurrence that can occur at anytime and any pressure, due to even a minor equipment failure. It doesn't automatically equate to human error. And if the operators were in fact in the process of flushing the system, and following the valve manufacturer's instructions, what grievous crime was committed?