**EDIT** I didnt see this was posted in the "ask a GM" section I didnt mean to step on any toes.

If you are reffering to traps set in areas like the Krandor Crypts for example. Each traps DC can be tweaked by the person creating the level. So I am not sure such an answer is possible, in the simplest terms.
Also there are 4 checks, Examine, Flag, Dissarm and Recover. each one is higher than the previous. In some quick testing of a simple area I created I placed some various gas traps the Examine was "X" DC, then Flag was 2 higher. Dissarm was 5 Higher than flagging, and Recover was 10 higher than Dissarm.
So to explain in this example on a Minor and Average Gas trap with no changes made to it.... it was 15 to Examine, 17 to Flag, 22 to Dissarm and 32 to Recover
But I could go in and adjust its DC if I so desired. and that would throw all those numbers out the window. follow me?
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