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While I could not find any case or authority that says that 1 inch is the minimum, the following Illinois case (Litchfield Healthcare Center v. Industrial Commission, 349 Ill. App. 3d 486, 812 N.E.2d 401, (2004)) establishes that a 1 1/4 inch rise between pavements to be hazardous: http://www.state.il.us/court/opinions/indcommn/2004/5thdistrict/june/html/5030632.htm
So I don't see how "2 inches" could be the minimum when there's caselaw that establishes 1 1/4 inch as hazardous. Now ultimately it's based upon reasonableness, so there's no minimum standard, but rather what would be foreseeable by the landowner as to what could cause injury or not. It might be less than an inch in a senior center, where individuals "shuffle" more, use walkers that have little ground clearance, etc... but be more in a situation where the individuals are foreseeably taking higher steps and less prone to trip in a situation such as this.
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate this answer either a 3, 4, or 5 (good or better). Please note that I do not get any credit for this answer unless and until you rate it that way. Thank you, XXXXX XXXXX good luck to you!
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