Its not the pH that's the hazard rather the chemical.  Sodium hydroxide solution even at pH 7-8 will react with the fats in the skin and over extended contact may defat the tissue.

Lynn K

---------- Original Message ----------
From: "Stuart, Ralph" <Ralph.Stuart**At_Symbol_Here**KEENE.EDU>
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Upper limit of pH hazards
Date: Mon, 31 Oct 2016 15:43:02 +0000

>I would caution saying that all pH chemicals above or below a certain limit are safe.  The characteristics, toxicity and permeation rates need to be thoroughly understood.

Good point, the way I framed the question was overly simplistic. My concern is specific to sodium hydroxide used to dissolve  excess materials on 3D printed objects. The question is how many rinses does it take for the rinse water to become non-hazardous.  

- Ralph

Ralph Stuart, CIH, CCHO
Chemical Hygiene Officer
Keene State College

ralph.stuart**At_Symbol_Here**keene.edu

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