Opens the Clash Detection tool is used to identify sets of elements to be used for the detection of physical clashes and clearance problems between the elements.  The clash detection feature allows you to identify sets of business or graphical elements and to detect geometrical clashes between these object element sets.  You can then interactively and graphically review these clashes, annotate or markup particular clashes, and assign them for follow-up.

• The Clash Detection tool can be accessed from Utilities ribbon tab under Clash Detection group:

• You have to create a new Job.  You have a Set A and a Set B between which you will be running the clash detection. 
• You can add your Soft Clearance.  This allows you to expand the space around an element so that the extra area can be calculated when executing a clash detection. 
• You can set up the clash detection between levels, or by looking at references or items between Named Group