A Human independent protection layer (IPL) can be a valid and valuable IPL. A human can be combined with an SIS-based alarm, but the human would then be part of the Logic Solver (decides what to do) and is part of the final control element. The criteria for counting human IPLs will be more completely defined in the upcoming textbook, Guidelines for Independent Protection Layers and Initiating Events, CCPS/AIChE, 2012 (pending early 2012). The human IPL needs to be specified and validated similar to other IPLs; part of the validation is testing of the hardware functioning up to the annunciation and part is testing (drills) of the human, who must complete the action (1) within the maximum allowable response time (MART) and (2) be out of harm’s way by then as well, since a human IPL is not valid if it places the responder (trouble-shooter) in harm’s way.