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PutACapInHisAss
Stranger Than Fiction



Registered: 08/11/07
Posts: 252
Loc: Earth
Last seen: 6 years, 4 months
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Understanding Laminar Flow Hood Use; Vertical vs Horizontal
#23528842 - 08/10/16 05:02 PM (7 years, 5 months ago) |
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I remember from an RR video that one of the critical factors in using an open flow hood horizontally is to not put gloves, containers, or anything with a contaminated surface between clean containers/surfaces and the filter.
All lab LFH's I've seen so far are vertical though. Is this just for convenience and comfort? They have bigger budgets? Or, is it practical in another sense?
It seems to me that one key with a vertical design would be not lifting possibly contaminated surfaces above clean containers and surfaces, maybe even elevating them to reduce this possibility. Also, as the air has to change direction 90 degrees to be able to exit out toward the hand access area, creating turbulence and direction of flow, maybe it would be important to also consider placement of items by similar reasoning--cleaner toward the back of the enclosure and dirtier items closer to the access area so that contaminates on them are exhausted outward.
Is this reasonable? If not, can you tell me the pros and cons of each approach, vertical or horizontal?
Is there a reason to have or not have an enclosed area around the HEPA exhaust on a horizontal setup?
Edited by PutACapInHisAss (08/10/16 11:32 PM)
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: Understanding Laminar Flow Hood Use; Vertical vs Horizontal [Re: PutACapInHisAss]
#23528849 - 08/10/16 05:05 PM (7 years, 5 months ago) |
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schools use vertical so they don't get damaged as easy Every beverage, beer or wine QA lab I've seen has horizonal hoods.
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PutACapInHisAss
Stranger Than Fiction



Registered: 08/11/07
Posts: 252
Loc: Earth
Last seen: 6 years, 4 months
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Re: Understanding Laminar Flow Hood Use; Vertical vs Horizontal [Re: bodhisatta]
#23532771 - 08/11/16 08:24 PM (7 years, 5 months ago) |
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What I am seeing common with fungus cultivators is the use of an industrial HEPA open to the air, and not having an actual hood. It seems they are using LF, and not the H.
More common from other resources is a setup with an actual hood which is what I have been planning anyway.
Here is advice I found about horizontal hood use:
“In a horizontal hood, items should be placed no closer than 3 inches from the very back of the hood (nothing should touch the filter)…When working in a horizontal laminar flow hood, all work must be performed at a distance of no less than 6 inches from the front edge of the work surface. At a distance of less than 6 inches, laminar flow air begins to mix with the outside air and contamination is possible. Never become so engrossed in your work that you forget this basic rule.” (http://www.globalrph.com/aseptic.htm)
If air begins to mix 6" away, and you try to stay 3" from the filter, this only leaves 3" of clean working space which is very small. Obviously fungus growers are using more space but I'm sure there is a limited window. Studying basic aerodynamics I have seen that air currents do crazy things and create back circling eddies. If air can circle back around and cause enough friction to slow down an airplane, it can surely circle back and contaminate objects in laminar flow.
If this is the case, and in light of the extreme cost of creating LF, an H just seems trivially more expensive and logical.
This raises the question: How big can or should I box it out to have a workable area?
Obviously, 3” + 6” burns up 9 inches if boxed out. How much space do you think is wise to put between these buffer spaces for a work area?
I think Plexiglass and Lexan are both commonly available in 24” widths. Running with this dimension would reduce cutting of an exotic material and provide 24” - 9” = 15 inches of workable space.
What do you think?
Edited by PutACapInHisAss (08/11/16 10:50 PM)
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PutACapInHisAss
Stranger Than Fiction



Registered: 08/11/07
Posts: 252
Loc: Earth
Last seen: 6 years, 4 months
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Re: Understanding Laminar Flow Hood Use; Vertical vs Horizontal [Re: PutACapInHisAss]
#23537903 - 08/13/16 12:53 PM (7 years, 5 months ago) |
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Supalemonhaze
Spore syringe hater.



Registered: 10/02/15
Posts: 6,725
Loc: 12" down Europe's butthole
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Re: Understanding Laminar Flow Hood Use; Vertical vs Horizontal [Re: PutACapInHisAss]
#23538050 - 08/13/16 01:45 PM (7 years, 5 months ago) |
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I wouldn't read too much into that 3",6" stuff. I've seen folks work with the jars almost touching the filter while doing G2Gs and I've personally put a plate as far back on the table as I can to see if it says clean, and it did. Mine is quite powerful though, blows ~220FPM out of the filter, twice the recommended flow.
Personally, I wouldn't build an enclosure. I use a hood so I won't be constricted to a box, not going to screw up the single most comfortable thing about a hood.
FH's the way most of us build them are great the way they are, enclosures are fine, even advantageous in some cases but not at all a necessity. If your hood is blowing at least 100FPM, normal room air currents will not disrupt it enough to interfere with laminar flow. Commercial hoods with enclosures often have a high and low setting, the low being something like 60FPM or something. If you had low FPM or strong air currents, an enclosure would be helpful but since you are going to build it from scratch, you can just build it up to spec and have more space to move.
If you are hell-bent on making an enclosure, you shouldn't attach it to the hood so it can be removed at any time. As well as making it only extend for a few inches, so you will have space to the side of the hood (outside of the flow) to move your arms and put your stuff. For example, if you extend the plexi or w/e all the way to where the table ends, not only will it be even less comfortable than a SAB but to put shit outside of the flow you need to take your arms all the way out of the enclosure. I have to say this again though, an enclosure in far from neccessary. I wouldn't do it.
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