We are a contracting firm that has worked on about a thousand perchloric acid hoods from New England to Florida to the Midwest over the past 23 years – CDC, FDA, universities, commercial/ industrial labs, etc.

The better places we have worked have a fairly short (1 page) form that incorporates elements of OSHA standards from 1910 and 1926: confined space entry, lockout/ tagout, fall protection, working and walking surfaces, heat/ cold stress, asbestos, and NFPA 70E and related regulations.  The first section(s) on the form(s) identify “ownership” of the exhaust system and possible contaminants.  From this section(s), a fairly simple hazard assessment or activity hazard analysis is done:  is there the likelihood that there could be a physical/ chemical hazard associated with the exhaust system?  If the answer is yes, then access is granted after the “owners” have cleared the area for access (with environmental/health/safety concurrence) from Level D (work clothes, no respiratory protection) to Level C or B (chemical protective clothing and respiratory protection appropriate to the hazard(s) and task(s)).  At the really good places, who regularly enforce their program, it generally takes longer to get a parking permit and after-hours access than to get roof access.  Sometimes it takes about a day to get roof access.

From the many comments already posted, if you think your facility is “good” by any definition, have an ASHRAE or other HVAC-type qualified person go on the roof with the fire department and the safety folks and look where exhaust systems and air in-takes are located.  As Gomer Pyle used to say, “Surprise, surprise, surprise.”

This is how we have handled it at the University of Arizona:  http://risk.arizona.edu/healthandsafety/ labchemicalsafety/fumehoodexhaustsystemmaintenance.shtml

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Ideally, if they are maintaining the fans and people are not using the hoods while they are working, there should be no problem.  I'd worry more about deposition of contaminants in the fans and ducts which sometimes occurs.   

But this is only true if the stacks and fans were properly designed and engineered.  Instead, what I see on the roofs of most university science buildings are rain capped exhausts or exhausts that are so low that the emissions will put workers at risk who are on the roof.  Hell, it's even worse than that--often the stuff is going right into the air handling units for the general recirculating system for the building.

If the building was built to the ACGIH Industrial Ventilation standards and to local department of environmental protection standards, those stacks would be tall enough or specially boosted to exhaust only into moving air above the building.  The height of the stacks should not be left to architects (who want no protuberances above the roof line) and engineers (who want to specify as much off the shelf equipment as possible).  Instead, the height should be determine by standards and regulations. 

If the stack heights are proper, the workers on the roof will not be exposed to the emissions.  If they are, maybe a redesign is the way to go.

Monona Rossol

In a message dated 10/30/2009 11:49:21 AM Eastern Daylight Time, stefan.w**At_Symbol_Here**UCONN.EDU writes:

In general, maintenance staff working on rooftop fume hood exhaust equipment have indicated their concerns about being on a roof, and possibly being exposed to whatever is being vented. 

In a more specific laboratory situation, involving MOCVD (metal organic chemical vapor deposition), we have a lock-out tag-out policy, due to the severity of the toxic gases involved.

 

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Does anyone else have MOCVD labs, and to what extent are controls in place for protection of workers on roof tops?
Does anyone else employ a LOTO policy?   
Are roof tops key-accessible only? 

Thanks for the feedback.

 

-Stefan Wawzyniecki, CIH, CHMM

  University of Connecticut