Solvent fume extraction help 1

[Waramanga]

Hi everyone,

What is the process for determining how to deal with fumes coming from a process using for instance solvents, or glue? My initial thoughts are obviously to catch it as soon as the fumes are produced, ie close to the bench. But how to determine the flows required, are there objective measures of air contamination in the operators breathing 'zone' or something like that?
Does anyone know of any companies that manufacture hoods etc for local extraction for benches and machines?
thanks for your help!

 

[Waramanga]

So I have been researching this in the meantime and I thought that I may as well share some of what I have learnt and ask another question or two. Ocupantional safety rules set the exposeure limit for various chemicals. The trick is to either determine how much exposure the people are likely to see in the 'breathing zone'. If normal ventilation rates will keep exposure below the threshold then all ok. Trouble is finding someone to accept responsibility for saying this. HVAC consultant cant and it is all really based on heaps of assumptions. The only real way of confirming the exposure levels is by testing a mock-up of the process.
The alternative solution is to collect the obnoxious stuff before it gets near a person. Firms selling the ventilation articulated arms say that they can do this effectively for low rates of fume production. I cant really see these arms working. The velocity around the intakes of these arms drops off with distance such that the arms needs to be right next to the work, like almost touching. Aside from putting the whole show in a fume cabinet, what other options/approaches could I take to this problem?

 

[ChrisConley]

My manual of industrial ventilation (21st Ed) has a stack of bench ventilation systems. We typically use an arrangement that places a slotted exhaust plenum along the front of the bench.

Push-pull benches are also recommended, depending on the process.

 

[IRstuff]

The generally accepted approach is some sort of fume hood, or a fully enclosed bax with gloves if toxic.

http://en.wikipedia.org/wiki/Fume_hood

TTFN

FAQ731-376

 

[SAK9]

You need to establish allowable OELs (Operator Exposure limits) for various materials being handled and the duration of these operations.Generally this information is available fromthe MSDS(Material Safety Data Sheet).If you refer to page 31 of the attached document it provides some guidance on containment strategies based on OELs to be maintained.If it isa contionous operation(as ia manufacturing environment,then a tested downflow both is the solution.

HVAC engineer is only responsible for designing a ventilation system to the the required OEL.If it is a critical application,go for the certified down flow both and get it off your shoulder!

 

[SAK9]

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[Waramanga]

Thank you SAK9 and Chris. Hey Chris, are you talking about the ACIGH book? I have ordered it because our ventilation code here in Australia says that if ventilation situation is not covered in the code then refer to that book. Does it have recommendations on design of workbenches etc? I can hardly wait to get my hands on it seeing
In you guys opinions/experiences, is it wise for a HVAC engineer design a system to conform to the exposure limits, leagally speaking that is, or do we not have any choice unless we just outsource the job to a downdraft cabinet maker? I mean, we put design basis in our specifications for temperature, occupancy etc. When doing industrial ventilation , would you do this with exposure levels? We have very well defined and easy to access standard for this here, the workplace safety authorities have a website with all this on it.

Thank you for your help....

 

[SAK9]

The ACGIH Industrial Ventilation is the bible for designing extraction systems.It advise you on hood sizes,capture velocities,distance of hood from source etc and it also provide OEL fora number of materials.

But be aware that extraction hoods or arms are used where the material is non toxic and the OEL levels are high because it is difficult to verify the OELs in such an installation.If you are dealing with more harmful substances the OELs are tighter and that will push you towards a tested downflow booth or even an isolator in the case of more hazardous substances.

Getting your designs reviewed by client's OHS/Risk&Safety consultant team is an insurance to some extent.Professionally your employer should know what your idemnity insurance covers you for.

 

[Waramanga]

Lucky for me the job is stalled for the time being so I have had plenty of time to chew on this one....

SAK, it turns out you are spot on, thanks! I have been digging around and it turns out that legislation (is Australia at least) makes the OHS outcomes of their workplace their problem that has to be dealt with be risk assesors who come up with a plan of attack. They indicate what measures they want to see to deal with OHS situations and then the Mech engineers provide a solution to help out. The ventilation is just one part of the puzzle and CANT be taken on its own.

I got that book ACGIH book, its great. A must have as far as I am concerned....

I am set for when they get the project rolling again.

thanks for everyones help