Finished making a biosafety cabinet aka tissue culture hood

[Abizar Lakdawalla]

Details for a diy tissue culture sterile hood made out of a room HEPA air purifier are at http://www.instructables.com/id/Biosafety-Cabinet-for-Tissue-Culture/

[Sebastian S Cocioba]

Do some sterility tests too. Leave some rich nutrient media plates like SOC or SOB media with no salt in the hood and open for 15,30,1hr,12hrs and incubate for two or three days at room temp and/or 30C. That should indicate if the hood is cleaning enough of the air. Have some plates outside the hood too. Maybe open one and do a pirouette to catch the particulates in the air around you. Good job on the instructables! 

Sebastian S. Cocioba

CEO & Founder

New York Botanics, LLC

Blog: ATinyGreenCell.com

On Dec 16, 2016, at 10:36 AM, Abizar Lakdawalla <abi...@gmail.com> wrote:

Details for a diy tissue culture sterile hood made out of a room HEPA air purifier are at http://www.instructables.com/id/Biosafety-Cabinet-for-Tissue-Culture/

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[Kermit Henson]

seems interesting...

nice job :)

[John Griessen]

On 12/16/2016 09:36 AM, Abizar Lakdawalla wrote:
> Details for a diy tissue culture sterile hood made out of a room HEPA air purifier are
> at http://www.instructables.com/id/Biosafety-Cabinet-for-Tissue-Culture/

I don't get where you say, "I decided to diverge from the standard design by a) pulling the air through the filter rather than
pushing it through which would result in less turbulence on the filter and b) having a bottom with a regular grid of holes so that
the air flow is more even - again less turbulence." Neither seems true to me, and there are few drawings.

"I decided to diverge from the standard design by a) pulling the air through the filter"

What does that really get you? Which filter? The one in the top of the diagram just below and left of your photo? One in
some other diagram?
The one if the middle of that diagram is also shown pushing through a filter. To me, pushing through a filter keeps all the dust
tenuously held on the helper fan vanes from getting through when it comes loose. Pulling makes for low quality of non-clean air
to my thinking processes.

"would result in less turbulence on the filter" I see many ways to design such that there is low turbulence on the filter.
The first way is to allow more space between. Another way is use baffles to guide air flows.

"having a bottom with a regular grid of holes so that the air flow is more even"

More even than what? There is only one diagram I find in
To me, having holes for return separated from the source of air by a cross section of the hood that is unchanging
is normal for creating laminar flow.


"The socket was attached to the back panel with a foam insert to prevent air leaking through the whole socket assembly."
I would allow some air flow to keep dust in the electrical box in the box by the negative pressure behind it.

Step 8 answers some questions. You show fans with no filter between them and the clean area. That is going to be subpar
for calling this a safety cabinet. To keep people from feeling overconfident while using your design with pathogens,
I would change the name to laminar flow cabinet. Biosafety cabinets have two filters and negative pressure in the hood
clean area compared to the room. Step 8 diagram says that your clean air flows out at the user through the access window opening.



A biosafety cabinet has keeping anything from getting out the openings
as its main goal, and being a good source of clean air inside in a zone is its secondary goal. So yours is not a biosafety cabinet.

Step 12 needs a listed electric box where the IEC socket connections to the solid wire are shown.

I like the use of plywood and super paint. That can be a real cost saver for a DIY hood compared to plastic.

You really should relabel this as a laminar flow hood or cabinet to be accurate.

John Griessen

[Abizar Lakdawalla]

HI John, good comments. Like some of your ideas especially on the power outlets, etc. BTW, I was a bio-scientist having done quite a bit of tissue culture over the years. My main issue was the damn weight of the overbuilt biosafety cabinets!

The cabinet has a particle sensor (from the RabbitAir air purifier) but it only detects > 1 um particles. Still have to add the UV lamps and normal illumination. And do a lot more tests over the next few weeks - including a smoke test to visualize air patterns and sterility tests. Will send out an update. 

1. On the push versus pull of air through the filter. I modeled this with COMSOL, and was a bit surprised. The model showed that when air from a centrifugal blower hits the filter with some force it dislodges particles on the surface of the filter. When you pull air through the filter fewer particles are dislodged.  I did talk to a building air circulation guy and apparently this is pretty standard thinking for HVAC installations but I will let other experts comments on that. 

Btw there is only one stack of filter (pre-, HEPA, and carbon). The grids are not filters.

The concept of an array of fans is also quite common - basically the air outflow is more laminar with many small fans than one large fan. As you pointed out you would need to channel air through overlapping baffles to create laminar air flows with a single fan. The array concept is actually pretty useful when you want to create planar flows versus point source radiation. It is used in lighting, in sound radiation (wall of sound - Bose has a stick speaker with a linear array of speakers), RF antennas, ... I spent a day with the fan placements trying to get uniform end-to-end airflow (at least according to my digital anemometer).

2. The only other major difference in addition to pull versus push is that the internal bottom of the cabinet has uniform holes. In commercial cabinets, these holes are only at the back of the cabinet (where the back vertical wall intersects with the bottom) and at the front of the base. My idea was that if I cover the base with a large tray I could easily replicate the standard configuration as then air would only move around the tray, essentially the back and front of the base.

3. Class 2 cabinets do have an additional filter. This is 30% the size of the main filter and is for releasing 30% of the air (filtered) to the outside creating the need for ~ 30% of the air being replaced by inflow from the front. Some of the commercial labs that I have been at seal this external outlet as they do not want 30% of air being sucked in from the front and instead prefer the filtered air being recirculated at 90+% (~10% is leakage through front).

Thanks again for your great comments

Abizar

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