Ralph,

Let me suggest that the "clean side" of a chemical hood includes things like drive belts and motors that are not in the air flow being exhausted. Fan blades would be on a "dirty side" as would the interior of the exhaust stack on the positive pressure side of the exhaust fan.

As to a hood-specific assessment lending itself to a "policy statement" - may I suggest that the appropriate policy statement or SOP would be one that lays out how to perform a hood-specific review of chemical work done in the hood, and, perhaps, some tests that might be appropriate in specified circumstances. (For example, rumor of hot perchloric having been use at some past time in that hood.)

Peter Zavon, MS, CIH
Penfield, NY

PZAVON**At_Symbol_Here**Rochester.rr.com

-----Original Message-----
From: ACS Division of Chemical Health and Safety On Behalf Of Ralph Stuart
Sent: Tuesday, April 12, 2022 7:38 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Hood Servicing SOP

> Usually the problem is a fan belt or motor that can be serviced on the 'clean' side.

I have addressed this question several times related to hood maintenance and each time a hood-specific review of the chemcial work done in the hood is necessary. This involves assessing what the possible contaminants of concern are likely to be present in the hood and ductwork and what sort of decontamination is appropriate. Given the wide variety of chemicals that could be used in a hood and the lack of information about quantities used, that can be a significant challenge. That approach doesn't lend itself to a policy statement very well.

Also, I'm not clear how the 'clean' side concept applies outside of radioactive materials hoods. Those hoods might have a HEPA filter in the duct to collect radioactive particles and the 'clean' side could be downstream of the HEPA filter? However, I don't know of any similar mechanism for chemical hoods, so I think everything downstream of the hood needs to be considered potentially contaminated (i.e. 'irty').

- Ralph

Ralph Stuart, CIH, CCHO
ralph**At_Symbol_Here**rstuartcih.org

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