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sonoramo
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Registered: 02/27/19
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Very low-cost one-hand HEPA tunnel
#27019547 - 11/03/20 02:13 PM (3 years, 2 months ago) |
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Here's how I've built a HEPA setup that serves limited needs but costs almost nothing to build, if you have a $49 desktop HEPA filter already.
This setup might be adaptable for grain-to-grain transfers or for inoculating jars and bags from agar. But that's not what I built it for. Instead, I use it only to work with agar on small petri dishes. The HEPA tunnel enables me to germinate spores, isolate strains, and then get a biopsy sample into a syringe and inoculate an LC jar. By not making the HEPA serve big objects, it can be much smaller and very, very cheap. Once I have a reliable and clean LC culture in a jar, all further inoculation goes by syringe needle through SHIPs.
First, the desktop air filter has to be one that can rest on its side, so that the clean-air exhaust blows horizontally into the tunnel. Many of the low-cost HEPA filters at Amazon are shaped like a cylinder, and it would be much harder to collect their exhaust and make it flow through the tunnel. I built the tunnel itself with cardboard, duct tape, an old yogurt-tub top and some self-stickfoam. The foam probably isn't really necessary.
The tunnel has three holes:
- A hole with foam around it to catch the HEPA exhaust stream.
- A small hole on the side to receive a sterile tool like a syringe needle or an inoculation loop.
- A hand-sized tunnel exhaust hole, which is where my left hand brings in petri dishes.
The extra cardboard flap from the tunnel goes under the HEPA filter. The filter's weight helps hold it in place so that clean air mostly goes through the tunnel.
I cut a round hole in the top of the tunnel and taped in the clear lid so I can see what I'm doing from outside.
I covered the inside of the tunnel with duct tape so that it's easier to wipe down than bare cardboard.
Obviously, you could spend a few bucks and modify a 6-quart tub or something like that instead of rummaging your recyclables bin as I did. Most tubs have sloping sides and that would make it a bit more challenging to get enough of the HEPA exhaust into the tunnel.
The tunnel is deliberately big enough only for one hand to be inside. To use, I wipe the work surface, the inside of the tunnel and the HEPA exhaust grille with my favorite sanitizer. Since only my left hand goes inside the tunnel, I wear only one glove. My right hand doesn't need a glove.
The HEPA filter is kind of old and it had a lot of dust inside from years of use. So I disassembled it as much as I could, washed and wiped the inside with alcohol and put it back together. I also replaced the paper filter. That was $12 for two from Amazon. If you buy a new HEPA, you wouldn't need to do this.
I've tested sterility by opening an agar plate inside and leaving it there for 90 seconds while running the HEPA. Then, covered the plate, pulled it out and sealed it with wrap. Two weeks later, the plate was still clean. I repeated it just to be sure. No contamination. A “control” plate on the outside, exposed to room air for 20 seconds and then covered, turned into a Biology experiment in a few days. My house is filthy with mold and that's what motivated me to do this in the first place.
The tunnel and HEPA. In use, the HEPA exhaust is right up against the tunnel "opening." You can see the foam I taped around the tunnel entrance to help force clean air into the tunnel.

Left hand (or whichever will wear a glove and manage opening the petris) goes in this hole. It is also the main exhaust hole from the tunnel. Tools go into the sterile space through the smaller hole on top.

Inside the tunnel. The duct tape is there to make sanitizing easier. And I had a roll of duct tape.
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deadmandave
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Re: Very low-cost one-hand HEPA tunnel [Re: sonoramo]
#27019686 - 11/03/20 03:09 PM (3 years, 2 months ago) |
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looks like a Shmuv box.
have you tried a still air box? probably a lot easier to work in.
must feel like youre trying to do agar work thru a port hole.
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sonoramo
Contaminant



Registered: 02/27/19
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Re: Very low-cost one-hand HEPA tunnel [Re: deadmandave]
#27019701 - 11/03/20 03:17 PM (3 years, 2 months ago) |
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Quote:
deadmandave said: looks like a Shmuv box.
have you tried a still air box? probably a lot easier to work in.
must feel like youre trying to do agar work thru a port hole.
For me, this is much easier than using an SAB (which I will repurpose because I don't use it anymore). The SAB needs much more counter space and a much cleaner place to work. I run the tunnel for 20 minutes or so before using it, similar to what I would do with the SAB. But this is less hassle for me. No need to scrub the room, change my clothes and all that.
Although my left arm has to be at a specific angle to use the tunnel, my right hand is totally free. It's easy to flame-sterilize a tool and stick it into the hole. With the SAB, both arms have to be at a specific angle to get in and out. And I have to minimize motion to avoid recontaminating the SAB every time I insert or withdraw an arm.
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bodhisatta 
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Registered: 04/30/13
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Re: Very low-cost one-hand HEPA tunnel [Re: sonoramo]
#27019740 - 11/03/20 03:30 PM (3 years, 2 months ago) |
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That's probably not a real hepa filter. And if it is it's not one that produces laminar flow anyway.
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sonoramo
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Loc: California, baby!
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Re: Very low-cost one-hand HEPA tunnel [Re: bodhisatta]
#27019783 - 11/03/20 04:04 PM (3 years, 2 months ago) |
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Quote:
bodhisatta said: That's probably not a real hepa filter. And if it is it's not one that produces laminar flow anyway.
Inside the tunnel, the flow evens out pretty quickly past the entrance. How would I test if it's a "real" HEPA filter? I have more agar plates left to test with,...
BTW, here's Amazon's description of the replacement filter: "Wolfish 2 + 4 Pack Allergen Remover True HEPA Filter Compatible with Holmes AER1 Allergen Remover True HEPA Filter, HAPF300AH-U4R"
Edited by sonoramo (11/03/20 04:08 PM)
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GrinchGrower
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Re: Very low-cost one-hand HEPA tunnel [Re: sonoramo]
#27019897 - 11/03/20 05:22 PM (3 years, 2 months ago) |
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dirtybirdx
getting better

Registered: 07/28/20
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Re: Very low-cost one-hand HEPA tunnel [Re: GrinchGrower]
#27019924 - 11/03/20 05:43 PM (3 years, 2 months ago) |
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lol.
I never do any of that cleaning the room, taking a shower, putting on clean clothes, brushing my teeth crap 🤣
It’s so completely redundant.
I have hundreds of hours in my cheap 6 year old SAB with sub 5% contam rate.
Cool little flowbox though if it works. Limiting on space but I could see it being useful for some agar work.
-------------------- Need help?

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Stipe-n Cap


Registered: 08/04/12
Posts: 7,623
Loc: Canada
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Re: Very low-cost one-hand HEPA tunnel [Re: dirtybirdx]
#27019932 - 11/03/20 05:48 PM (3 years, 2 months ago) |
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That thing will create turbulence, turbulence = contamination. Even with laminar flow turbulence will contaminate your work. People are under the impression that filtered air is all that you need. Filtered air is irrelevant if its turbulent, the filtered air may be sterile (if you've chosen the correct filter and matched it to an appropriate blower) but you and your environment are not and never will be. Your constructed environment is full of imperfections that will cause turbulence, the walls floor and lid, your arms, hands, clothing, and hardware all cause turbulence.
You're in the r&d phase. This contraption hasn't been proven to reliably produce results and is therefore not a tek.
 
Turbulence creates eddies exactly like the turbulent water that forms behind a rock in a stream. Those Eddie's will pick bits of pollen, skin particles, dust etc from your hands, arms and clothing. They will then be carried around the interior of your box riding those currents directly into your open petri or jar.
This is why you never place your hands or tools between the clean laminar flow of air and your work while using a clean bench. The same principles apply here.
Edited by Stipe-n Cap (11/03/20 06:09 PM)
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sonoramo
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Re: Very low-cost one-hand HEPA tunnel [Re: Stipe-n Cap]
#27019980 - 11/03/20 06:30 PM (3 years, 2 months ago) |
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Quote:
p9hu7 said:
Turbulence creates eddies exactly like the turbulent water that forms behind a rock in a stream. Those Eddie's will pick bits of pollen, skin particles, dust etc from your hands, arms and clothing. They will then be carried around the interior of your box riding those currents directly into your open petri or jar.
This is why you never place your hands or tools between the clean laminar flow of air and your work. The same principles apply here.
Definitely the (commercial) construction of the HEPA with the blower on the downwind side of the filter creates turbulence. Worst of all, it would probably dislodge crap stuck to the interior walls near the fan and those will fly willy-nilly downwind. Definitely the tunnel entrance and other obstructions in the flow create nonlaminar flow, eddies and so on. Crap will deposit preferentially in the slow-flowing eddies.
On the other hand, with only one hand in the clean area and downwind from the dishes, there should be less turbulent flow. It's hard to imagine that a slender syringe needle or inoculation loop holder would create enough turbulence to cause trouble.
So how would you go about "proving" or "disproving" that it is useful? How long, for example, could I leave an opened agar plate in a "real" flow hood and expect it not to get contaminated? Minutes? Hours? I've tested three plates inside so far. Two were longer exposures with the blower running. I thought, "maybe it will operate more like an SAB if I turn the blower off." So I turned the blower off, waited a few minutes and then opened a plate for two minutes. It contaminated. The plates exposed with flowing air didn't contaminate. So maybe I happened to get two anomalous results. One plate exposed to my nasty home air for 20 seconds outside the tunnel got really contaminated.
Who wants to suggest a test so that I can get a valid result, pass or fail? I have more plates to test with. Or is there some other test to try?
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Stipe-n Cap


Registered: 08/04/12
Posts: 7,623
Loc: Canada
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Re: Very low-cost one-hand HEPA tunnel [Re: sonoramo]
#27020021 - 11/03/20 06:53 PM (3 years, 2 months ago) |
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Everything that you do withing the flow generates particles. Because you don't have laminar flow you do not have the benefit of unidirectional airflow to protect your work from the movements that generate particles. This is why you need to use slow deliberate movements in your SAB so as not to disturb particles that will become airborne and mobile on the eddies generated by your movements. Due to the turbulent environment you won't have that protection either, there will only be turbulence, no still air and no unidirectional flow.
The best way to visualize this would be with a smoke test, this will show you how the particles will be flowing within your environment. You don’t need to open plates or anything, the particles are surely there, all you need to see is how they're moving.
You will have some success using this, of course. You would have success in open air. How much margin of error are you willing to accept? Using one or two petri dishes will not give you a reliable sample. The science has already been done sufficiently in other areas to make a pretty definite conclusion regarding this design.
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