Ductwork for laboratory exhaust

[remp]

Im currently buildig a laboratory facility for a hospital. The contractor has specified all poly propelyene (PP) ductwork and fans for the extract from the Fume hoods and the local extract arms over lab benches and the solvent storage room.
I think this is total over-kill and is costing us a fortune. Especially for the local extracts that suck room air 99% of the time. Fume cupboards also suck majority room air with some acid/solvent vapour i suppose.
I am thinking of doing Galvanised sheet metal duct thro' out....that do you think? any commenct before its too late???
last year I modified a lab and all the existing Galvanised local exhaust was in good condition.

 

[trashcanman]

First, what is your function? You say you are "building" a lab for a hospital. Literally? Are you actually in the field hanging duct?

Are you the engineer working for the contractor? Whoever signs and seals the drawing specifies the ductwork material, not the contractor. If so, check the properties of what you are exhausting and see if galvanized steel is really suitable. Depending on how corrosive the fumes are will dictate what material to use for duct and fans.

 

[SAK9]

In my opinion GSS will be okay the reason being the exhaust air is highly diluted(typical air change rates for labs being 20~30.I had raised the same concerns many years ago on a chemistry lab project and the team did a bit of research and we came to the conclusion that GSS will meet the requirement due to the low concentration of chemicals present in the air.However if you are extracting perchloric or similar acid fumes,there is a good chance of the acid condensing inside the duct in which case a compatable duct material is required.Anyway acid hood exhaust needs to be on a seperate duct so it would not be too expensive to have it done in a better material

 

[Wareagl487]

I would be careful with a substitution without consulting the designer - He specified that material for a reason.

I was involved with a large lab facility for Smith Kline a number of years ago. All exhaust ductwork was stainless steel. They were doing something real nasty under one of their hoods and it ate up that stainless in just over a year.

Andy W.

 

[ChrisConley]

I think this is total over-kill and is costing us a fortune.

Was the contract bid with the PP duct? If the contract is to build the project with PP duct, and the only argument against is that it is costing you money... not really a good argument.

With no knowledge of the processes beyond that someone has specified PP duct, I would be extremely reluctant to change the ductwork. Particularily to standard sheet metal.

 

[daly1]

The fume cupboard comment leads me to believe your in Europe and thus the possible use of PP. Need to approach this scientifically and relaying a 'I modified a lab last year where Galvanzied duct was used" should never be used to justify the next project's decisions. The chemistry changes literally (typically) room by room and cupboard by cupboard.

First there is no requirement to always separate acids from other exhaust streams (couple exceptions). In the US we are required to provide separate exhaust streams for radio-isotope AND perchloric acid exhaust fume hoods. Convention also tells us that other dangerous materials like Hydroflouric acid and others are also separated as part of a risk avoidance component of the hygiene plan. So look into the chemistry and ask a chemical engineer to advise you based on the corrosive properties of the actual chemistry being done in the fume hood.

Remember, you're building a lab to last 50 years. The chemistry being used today will change 10 times over the life of the building. I have used galvanized on many fume hoods, I have used stainless on the first 10-15' then transition to galvanized (discerned multiple hot plates would be generating excessive steam and there was a concern over condensation), and have used FRP, PP, and other compostites. Typically, the composites offer superior resistance to corrosion but cost 1.5-3x, longer install time, and in Europe you probably are faced with sprinkling the inside of your exhaust.

make sure your fume cupboard supplier is providing you with combination sashes. The horizontal components are needed to provide an explosion/blast and splash barrier. You folks in Europe don't have to follow OSHA but providing the proper control barrier--especially with the use of solvents and other reactive chemistry--should be a base requirement on every single fume cupboard.