Question from an amateur about laminar flow hood

[Hany Saad]

Hi,

My name is Hany Saad and I work as an intern at the FabLab Amsterdam (Waag Society). Together with my colleague, I am building a laminar flow hood. During our research, we had the chance to disassemble an actual hood. It was a nice project, but it did left us with some questions.

When we opened up the back, we saw that the blower was attached directly on top of the HEPA filter. Next to the blower was a duct, which connected the inner workspace with the top of the cabinet through a filter. This filter on top also contained the airflow sensor.

My question is this: Can somebody explain to me how the air flows through this system? For us it was strange that the filter and the top were directly connected to each other. Also, the airflow sensor was attached to the filter on top, which seemed kind of odd (see sketch) I included pictures, plans and sketches of the cabinet. Don't mind the arrows, 

Thanks in advance

[John Griessen]

On 03/18/2015 06:10 AM, Hany Saad wrote:
> My question is this: Can somebody explain to me how the air flows through this system?

Before I saw the biohazard emblem on the drawing I thought:

The part the blower is attached to lets air out the duct and aims down into the flow bench area.

The flow bench space has a positive pressure due to the blower pushing air in faster than
it goes out the front and the duct. The amount of air going out the front varies all
over as the front door is raised or lowered.

The duct top part seems to be a variable outlet opening like a vent for a HVAC system,
and it has a sensor so that if the flow there drops too low, an alarm goes off, or the level of pressure there
goes to a readout of some kind.


Instead, *with* the biohazard emblem:

The part the blower is attached to only lets air out the duct. It pulls air from the slots at the back.

The flow bench space has a negative pressure due to the blower pulling air out faster than
it comes in the front. The amount of air going out the front varies all
over as the front door is raised or lowered.

The duct top part could hold another filter, and it has a sensor so that if the flow there drops too low, an alarm goes off, or
the level of pressure there goes to a readout of some kind.

[John Griessen]

On 03/18/2015 09:18 AM, John Griessen wrote:
> comes in the front. The amount of air going out the front varies

should be:

> comes in the front. The amount of air coming in the front varies

[Nathan McCorkle]

This is my interpretation of what the airflow might look like:

https://awwapp.com/s/c8/c2/53.html

with some mixing happening when the two streams first meet and 'touch' in the picture (at the top of the inner chamber).

Now since these blowers are not in the same spot, but adjacent to each other.... I'd guess there's be some (vague probably) corkscrew like action going on too (along the length of the opening) maybe like this:

https://awwapp.com/s/9b/32/11.html

I bet we could model and simulate this... something I've been working on but haven't had much time to work on lately.

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[Patrik D'haeseleer]

What you have is most likely a Class II, Type A2 Biosafety Cabinet, since that's about 95% of all biosafety cabinets out there. A Class II BSC is what is needed for a BioSately Level 2 lab: it protects you and the environment from what you're working on, and it protects what you're working on from you and the environment.

This type of BSC actually sucks some amount of air IN from the front, directly into the grill at the bottom of the sash (the glass panel in front). About 70% of the air inside the cabinet gets recirculated through the HEPA filter, and 30% fresh air enters through the front.

Lots more info here: 

http://en.wikipedia.org/wiki/Biosafety_cabinet#Class_II

http://www.bakerco.com/introduction-biological-safety-cabinets

[Patrik D'haeseleer]

By the way, don't just call it a laminar flow hood, this is a biosafety cabinet. Laminar flow is a property of many different types of enclosures, including biosafety cabinets, some types of chemical hoods, balance enclosures,etc.

Typically, a "laminar flow cabinet" ONLY provides laminar flow, but no biological or chemical protection. For example, laminar flow cabinets used for plant tissue culturing push a curtain of filtered air from the back of the cabinet, over the work area, towards the user. This type of hood would be entirely inappropriate to use with pathogens, engineered microorganisms, or toxic chemicals, because it provides zero protection to the user.or the environment.

Likewise, a chemical hood or fume hood is NOT the same as a biosafety cabinet. A BSC uses HEPA filters to filter out potentially infectious particles. A chemical hood uses activated carbon filters or an external exhaust to deal with toxic chemicals. But you do NOT want to use biological materials inside a chemical hood, because it is absolutely not designed to contain those. And you do NOT want to use any fuming chemicals in a biosafety cabinet, because they will just pass straight through the HEPA filter and get exhausted into the air.

TL;DR: use the right tool for the job! A laminar flow hood is not a biosafety cabinet is not a chemical hood.

[Hany Saad]

Thank you very much. This makes total sense.

Op woensdag 18 maart 2015 16:23:45 UTC+1 schreef John Griessen:

[Hany Saad]

Could you elaborate on the "cork screw action" you were talking about. The fan and duct are next to eachother.

Op woensdag 18 maart 2015 20:17:24 UTC+1 schreef Nathan McCorkle:

[Hany Saad]

You are right, I wasn't clear. I meant to say that we are building a laminar flow hood and we had the chance to disassemble a biosafety cabinet. 

In all honesty, I thought the terms were interchangeable, that's what I've been taught, but as I said, I'm an amateur. 

Op donderdag 19 maart 2015 09:56:45 UTC+1 schreef Patrik D'haeseleer:

[MikeCZ]

Hello, do you have experience with this laminar flow cabinets?

[S James Parsons Jr]

What questions do you have about laminar flow hoods?

On Mar 28, 2019, at 3:40 PM, MikeCZ <ondra...@gmail.com> wrote:

Hello, do you have experience with this laminar flow cabinets?

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