This is one of my prefered utilities, the Filter Daemon. You can use it to kill, separate or split particles into more, it is a really cool tool. The best of this daemon is it saves time in scripting similar tools and computation time, because it is built as other multithreaded daemon in the core of RF. I´ve used it in this example to fake a melt effect.
This video shows the filter evaluating the position in Y axis.
In this example is being evaluated pressures.