From: ACTSNYC**At_Symbol_Here**CS.COM
Subject: Re: [DCHAS-L] Toxic dust handling
Date: June 28, 2012 2:47:13 PM EDT
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: <28c3.5919e01b.3d1e00b1**At_Symbol_Here**>

Ken,  I wondered when this question would come up.  There used to be a 10 mg/m3 TLV-TWA for silica gel, but it was withdrawn for lack of data.  And now, based on studies of very fine (respirable) inert particles in general, I would treat the stuff as potentially hazardous.  So I for one, was glad to see this discussion rather than to have people plan no precautions because technically only the SiO2 contaminant is regulated.

If it is any help, NIOSH has a 6 mg/m3 REL-TWA for silica gel itself and the DFG MAK-TWA for two amorphous silica forms diatomaceous earth and fused silica in respirable size particles is 0.3 mg/m3.  As for the SiO2 contaminant, it has a MAK 1 rating, meaning employers must use every available technology to keep exposure to this cancer-causing stuff as close to zero as possible.  They don't set exposure standards for MAK 1 carcinogens since they understand that the decision on just where to set the workplace limit is literally a discussion about how many workers it is acceptable to do in.

I think I see a TLV coming down the pike from ACGIH in the future.


In a message dated 6/28/2012 8:27:26 AM Eastern Daylight Time, kwkretch**At_Symbol_Here**NCSU.EDU writes:

I think this is a very useful discussion.  I'm curious about the original mention of silica gel which started this thread.  For those of you who may handle this material in bulk, is this silica gel (amorphous silica) expected to be contaminated with crystalline silica which is the toxicity concern ?

Director, Environmental Health and Safety
NC State University
Raleigh, NC 27695-8007

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