low cost positive pressure laminar flow HEPA filtered box

[John Griessen]

On 07/18/2014 04:30 PM, Nathan McCorkle wrote:> I think common lingo just calls what you're describing a clean air
> hood, nerdier folks call them positive-pressure hoods.
>
> I could be wrong, but that's been my understanding for the past 5 years or so.

A hood suggests a vent to a duct in the building, so I did not want to talk that way.
Leaving out the words laminar flow would be such low braggability...

So how's the new subject line sound?

On 07/17/2014 11:00 AM, CindyB wrote:
> If you flood your intake side with particles to see how many get through you will have used up the fouling capacity of your filter
> with your test.

There must be some way such tests are done without using up the filter, because some companies brag about it.
By flood, maybe I used the wrong, non-quantitative word. They probably do not use a shovel to add
test sphere particles, but a puffer, duster, air siphon mixer of some kind similar to a siphon spray gun for liquids..

In industrial manufacturing HEPA flow hoods, tests consist of:1) testing flow rate of air on the clean side;
> target: not too fast, not too slow 2) industry standard particle detector test on the clean side; target: no particles in
> detection range 3) pressure drop across the filter; target; not too high
>
> I didn't give quantitative targets because it depends on the industrial requirements. I could see a low budget way of assessing
> flow rate with a small strip of cloth as in a wind sock and a home made water manometer (for pressure drop). Not sure how to get
> the particle detection.

What do you think of this:
http://www.sca-shinyei.com/pdf/PPD42NS.pdf

[CindyB]

The link takes you to a particle detector. It would have to be built and, more importantly, maintained/calibrated to be a measurement tool that could direct action. While a (maintained/calibrated) particle detector would help find particle leaks inside your clean chamber, it wouldn't tell you something more relevant to your goal: reproducible inoculation of growth media. If that's your goal, that's what you should measure. That looks to be the point of this comment:
https://groups.google.com/d/msg/diybio/9-A-EHhJxN4/PYVnNiUrMK8J
There is probably an official name/test protocol for it but let's call it the Petri test for this commentary. I will happily change what I call it if someone has a link to the protocol for this type of test.

Cheap "is-air-flowing" indicator (the scrap of fabric-> wind sock) and a cheap "is-the-filter-too-spent" indicator (manometer) are indirect measurement of your target result (reproducible inoculation) but they are cheap and their measurement directs action (turn on air flow motor and time to change filter). The problem with the Petri test is, on failure, you have to do more and different tests to direct action. Over time, you would probably develop Petri test data patterns for your clean hood that provide enough information to direct action.

I wonder if you could assess sufficient keeping-stuff-out by a different take on helium leak detection? The measurement of relative humidity is fairly well characterized. An Arduino version can be obtained very inexpensively. With a modicum of care, the RH meter can be maintained cheaply. Set the RH meter inside the clean box, close it as in regular use, spritz water or run a water-soaked cloth along ostensibly sealed outside edges while watching the meter. If there is an outside to inside path for the water, the RH will rise. This gives you information to direct action, too.

Cindy

[John Griessen]

On 07/28/2014 04:15 PM, CindyB wrote:
> If there is an outside to inside path for the water, the RH will rise.

Thanks for thinking about this. Water will always flow freely through a HEPA filter made
to filter 0.3 micron particles to a degree of 99.97% or 0.9997 fraction of all air going through it.
That means RH would not tell you about particle filtering ability.

I am interested in ways to use the industry standard filter characterizing measurement stats to show meeting them
for reasons of convincing others or your own group members your filter is adequate
without doing long term experiment design. Some may want to maybe do such long term experiments,
but they would never buy a filter that did not minimize the chance it would be to blame.
I'm wanting to sell filters, so characterizing them to compare price and performance with standards is
essential.

One industry standard about quality of construction of seams is to squirt an air suspension of
0.3 micron particles, (the hardest ones to filter out), at seams and count particles downstream,
noticing any spike of particles counted after spraying seams. That's what I am thinking of the
particle detector for.

Measuring the 0.9997 fraction sounds very difficult to do -- best left to labs for characterizing
filter fabrics.

Looking for spikes in time of particle counts while blasting the outside of a filter will show 2 defects
of manufacturing: A frame seam not sealed, or filter material that has been folded too sharply and broken through
so that particles go through a ragged tear in it. It will work even with a used filter.

For hood owners to have their own particle counter will help them
determine if their filter is damaged by rough handling, or if a new filter
has been installed loosely with a gap that is leaking dust. It will let
them break free of the "certified by X high priced seller" trap, since they can compare themselves
and so self certify.

[Cindy B]

Ah. Got it. Industromatic and Cibolo are for profit businesses aimed at the DIYBio and early start-up Bio. There are other goals than "reproducible inoculation".

I wouldn't put water in/near the HEPA part... just the various edges for debugging after a failed Petri test.

Best of luck,

Cindy

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[Ilya Levantis]

I recently built a HEPA airflow box for the London Biohackspace. And we just did a quick petri test. And since the initial results were much better than anything we were able to achieve with our previous bunsen method we have decided to plow on and start using it. As regards testing, we have marked out 8 positions for petri dishes, every time we use the flow box we'll note down the position each petri dish was plated/innoculated on and check dilligently for contamination after incubation. From this we should start to build up a reasonable data set about likelihood of contamination based on the spatial location in the "clean" work area.

I wrote up a blog post about the construction if you're interested: http://biohackspace.org/building-a-diy-flow-hood/

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[John Griessen]

On 07/29/2014 09:41 AM, Cindy B wrote:
> for profit businesses aimed at the DIYBio and early start-up Bio

Also aiming to lower the sale prices of even the highest quality lab gear by
promoting comparison shopping opportunities to all. I won't be going after any
large systems built into buildings though. I'll influence from the domain of UPS/USPS/Fedex
shippable instrumentation and process equipment.

> I wouldn't put water in/near the HEPA part... just the various edges for debugging after a failed Petri test.

OK. Water vapor would still flow freely through undamaged HEPA filter media, so it's not a positive test of leaks.
It might show some flow patterns -- needs some testing to tell.

[John Griessen]

On 07/29/2014 09:52 AM, Ilya Levantis wrote:
> From this we should start to build up a reasonable data set about likelihood of contamination based on the spatial location in
> the "clean" work area.
>
> I wrote up a blog post about the construction if you're interested: http://biohackspace.org/building-a-diy-flow-hood/

Sounds good. Thanks!

I took a look at your biosafety purpose vertical flow hood and the amount of air intake slots
that pull from the glass shield area seems skimpy.


I think if there really is danger, you would
want a set of ten rows of intake slots in front all creating laminar flow that pulls in some air from the
shield so there is no way bugs get out. What happens as you put your gloved hands through that area?
The laminar flow is all broken up then...

I'd prefer sealed glove boxes that can have a decontamination process done with the gloves
and disinfectants that are always on hand inside, and sterilizing air locks.

But then, I'm not interested in researching pathogens or toxics either.
The most I'd use that design for is to avoid stinky cultures effects on the room
when used with an exhaust duct to the building outside.

[CindyB]

Sorry. Made some assumptions about knowledge of helium leak testing. Here is the procedure:
http://www.tqc.co.uk/leak-testing/leak-testing-guide-to-helium-leak-testing.php
See the section titled: "Background helium concentration" for techniques to aid in leak detection. There is some skill required in how to apply the helium (or water vapor per this recommendation) to aid in leak checking. This approach to leak checking is not novel.

Regards,
Cindy

[M DembMicky Dembek]

Hi

I have seen one instructable on building a laminar flow hood, I have even made one myself....but it looks awful. I guess i'm not this good at DIY afterall :D

Searching through ebay you can't find anything at decent price.

Today I have made a discovery. 

Since i've only got little space for my 'lab' at home, big and expensive hoods were out of the question-hence my failed attempt at building one.

I have searched through alibaba.com this chineese ebay. The prices they sell some equipment for.... I have enquired on availability and the total price of one cabinet called Biobase, The size is ideal for my place, and they claim that their product is consistent with European Standard EN13469:2000, and filter 0.3 micron particles. and all of this at the price of about 350 british pounds!

[Dakota Hamill]

I've seen and talked to so many people that just have a fan blowing through a HEPA filter, without a side box, and they barely get contamination.  Some people just drop a giant clear plastic thing over themselves and crawl under it after its attached to the filter.  All the eddy currents and BS, I don't buy into it, because i've seen some ghetto setups that don't get contaminants.  Just throw your jars in front of a decent hepa with a decent blower and you'll be fine.  Don't order from Alibaba, plenty of american companies that will do it for that price or under, and you won't deal with customs or 1 month shipping

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[scoc...@gmail.com]

I like the quick and dirty hack of buying a standard room air purifier (true hepa) with a vertical output and ducting it to the cut out top of the biggest clear Tupperware storage bin you could find. Run some T5 shop lights and its good to go. No need to reinvent the wheel with a home made hepa box when u can get cheap precision engineered hepa filter blower combo from a repurposed retail device. All you need is to cut a circular hole for the duct and a rectangular hole for your hands.  Simple and it works.

A friend Alex Pfrogner off this list made one and it worked well for him. He did a 24 hour constant flow test with open Petri dishes with LB against a stagnant air control plates the bench next to the hood. The experiment gave no contamination on the plates that were left open in the hood vs some growth on the bench top ones. All playes were LB and incubated at 37C for 24 hours after the 24 hour room temp air exposure. Case in point its simple and it works very well.

Sebastian S. Cocioba
CEO & Founder
New York Botanics, LLC
Plant Biotech R&D

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From: M DembMicky Dembek
Sent: ‎1/‎25/‎2015 11:08 PM
To: diy...@googlegroups.com
Subject: [DIYbio] Re: low cost positive pressure laminar flow HEPA filteredbox

[Alex]

+1 Works wonderfully!

To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/54c5c73b.455a8c0a.5ece.097d%40mx.google.com.

[Dakota Hamill]

post some pics of your sweet rigs and plates.

actually that's another thing, the home tissue culture forum (Even though yahoo sucks) has tons of pictures, but I rarely see any pictures posted on this list.  I suppose there isn't a direct way to post pictures to the group as a whole, is there?  Can you send an attachment to 3k people?

To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/CAKgQa2OkZvAXeJJMVPO3H%2B7JgeWCz_z7DQGfc_Pr%2B9_3Q2jbGg%40mail.gmail.com.

[M DembMicky Dembek]

i'm actually doing exactly the same thing. I've got Vax hepa filtered air purifier for 25 pounds of ebay. I will see how it works :)

Regarding customs I've got a microscope from India, it took 5 days to arrive. Customs cleared in one day. 

[Patrik D'haeseleer]

'Tis the season to build laminar flow hoods! BioCurious and Counter Culture Labs each independently acquired a Flow Sciences vented balance enclosure that we're planning to convert to laminar flow hoods .

The mushroom and plant tissue culturing communities have been making DIY laminar flow hoods for ages, and have some very well documented builds. Here are a bunch of good resources:

http://www.orchideenvermehrung.at/cgi-local/framebreaker/reload.pl?english/lfh/index.htm

http://www.fungifun.org/English/Flowhood

https://mycotek.org/index.php?threads/evilmushroom666s-flowhood-build.49/

https://mycotek.org/index.php?threads/insects-2x4-laminar-flow-build.4674/

[Otto Heringer]

There's also this well documented tutorial. The results looks nice.

http://hackteria.org/wiki/DIY_Sterlisation_Hood

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[Patrik D'haeseleer]

On Tuesday, January 27, 2015 at 4:54:22 PM UTC-8, Otto Heringer wrote:

There's also this well documented tutorial. The results looks nice.

http://hackteria.org/wiki/DIY_Sterlisation_Hood

That one is definitely not a laminar flow hood though. For laminar flow, you want the entire air mass to move as one smooth sheet towards you (or form the ceiling to the floor, in vertical laminar flow). 

 

Because the Hackteria design only has one small cylindrical filter, the filtered air will flow out from there with lots of turbulence, and that turbulence can suck in contamination from the front of the hood. There's also no way they can match the recommended air volume of 100ft/min with a filter that small. 

The professional and DIY laminar flow hoods I've seen typically have a large rectangular HEPA filter that takes up the entire back surface of the hood, allowing the entire air volume to move towards you in one uniform mass. One of the links I posted above suggests how to check for laminar flow with a lighter: the flame of the lighter should be moving straight out away from the filter without any flickering whatsoever. That's a LOT of airflow!

Patrik

[Cathal Garvey]

Could you mimic this though, by passing air through a HEPA and then
having it (inside the sterile space) pass through a lint-free,
pre-sterilised fabric sheet?

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[John Griessen]

On 01/28/2015 07:57 AM, Cathal Garvey wrote:
> Could you mimic this though, by passing air through a HEPA and then having it (inside the sterile space) pass through a lint-free,
> pre-sterilised fabric sheet?

Yes, and that would protect your filter from splashes also. Muslin might be right for it, or maybe cheesecloth...
The filter still needs to flow slowly enough to work well,
so it still needs to be large enough...just how large is probably a measure-test-repeat-while-necessary design process though.

Fabric must seem too "homey" to be an industry standard. The industry standard way you see in ads is a filter,
then a plenum, (or manifold), then a panel with slots to release
the air. The panel is the full size of the back of the rectangular box of the flow hood. I'm sure some kind
of stretched fabric could do even better at laminar flow than a panel with slots.

Probably the wall of slots is the best compromise between needing to "change the sheets" often, and having a little
dust left after wiping down the front surface of the wall of slots. Since we think of a flow bench as durable,
there needs to be a way to clean it.

[Cathal Garvey]

I can't imagine "lint free" can be guaranteed enough for industrial
standard with a sheet, either. At least, not with a sheet that's cheaper
than a large HEPA filter in the first place.

[Ilya Levantis]

I'm extremely dubious of set ups using the air purifier HEPAs. I managed to get a specification and test sheet from a typical supplier of those filters (https://www.dropbox.com/s/1i7qo8v6xgxwov7/DOP%20test.pdf) and it suggests to me you would never be able to get laminar flow going from one of those - you would probably need some huge fan or an array of leafblowers to actually push enough air through them, and by that point the actual particle catching efficiency would probably not be as effective.

But some people appear to be having success with such setups - I'm curious to know more.

[John Griessen]

On 01/28/2015 11:31 AM, Ilya Levantis wrote:
> you would probably need some huge fan or an array of leafblowers to actually push enough air through them, and by that point the
> actual particle catching efficiency would probably not be as effective.

Sebastian's mention was use a clear plastic box. I bet that works with the usual low flows of the
air purifier HEPAs.

One way to use low flow is by having the flow go down and out, and the exit is between the suspended edge of the box
and a table top. The exit could be just enough to get hands in.

Otherwise, if the usual box with one side open is used, hang a clear screen from the front open edge down to just have
1/4 of the front open -- also enough to get hands into. Then you use less flow, smaller filters.

[Cathal Garvey]

I've had good success with a simple positive pressure glovebox with a
large HEPA filter for large rooms; high enough pressure that tools would
get blown out of the work area, in fact.

It worked great, no contaminations.. until the HEPA filter saturated on
mold spore in an old building where I hosted workshops, and that was
that. I never replaced the filter as I had little need; I'd secured a
bunsen and a safe work-space on which to light it.

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[Patrik D'haeseleer]

On Wednesday, January 28, 2015 at 7:04:49 AM UTC-8, John Griessen wrote:

The industry standard way you see in ads is a filter,
then a plenum, (or manifold), then a panel with slots to release
the air.  The panel is the full size of the back of the rectangular box of the flow hood.  I'm sure some kind
of stretched fabric could do even better at laminar flow than a panel with slots.

That panel actually houses the HEPA filter, as far as I know. There typically is a filter at the air intake as well, but that's just a cheap filter pad to keep out the larger dust, not an actual HEPA filter.

Patrik