Extract from the 3ds Max definition:

“An element is one of two or more individual mesh objects (that is, groups of contiguous faces) grouped together into one larger object. For example, if you attach one box to another, you create one mesh object from the two boxes. Each box is now an element of the object. Any function you perform on that object affects all its elements. However, you can manipulate the elements independently at the Element sub-object level.”

In the case of thinkingParticles “Elements” should be in fact split down to a proper object with a water tight surface not showing any holes in it. Clean modeling, right from the beginning of the project, is the only way to guarantee proper physics simulations at a later stage. Bad models will later result in funny or unrealistic physics simulations - keep this in mind when handling complex projects were the origin of the 3D models is unclear.