Air lock to prevent Flow of Contaminants 1

[Buildtech2]

In my current project, I have to prevent transfer of contaminants from antibiotic lab to the production area. The antibiotic lab and storage / production area is seperated by a link bridge. Though antibiotic area is kept at negative pressure with respect to the link bridge but it is still considered as sterile area and we need to wear protective clothing to enter in the lab. In all cases, the contaminatns are not allowed to enter into the lab through production / storage area and vice versa but conveyer will pass through the lab to the warehouse area through a link bridge and there will be opening between between the lab and the link bridge.
To prevent the contaminats to flow in either direction, I have now decided to provide an air lock in the link bridge with duty /standby exhaust fan on the roof of the link bridge.The exuasut fan will exhaust air from the air lock and hence it create an air lock between the lab and warehouse / production areas. I would like to know the following.

1. Is there any other better strategy to prevent the contaminatns to flow from production area / warehouse to the lab and vice versa.

2.The suitable type of exhaust fan to be selected.

3. How much exhaust air to be exhausted from the air lock to create an proper air lock to prevent the contamination flow in either direction.

 

[quark]

Can you attach a hand sketch for better understanding? what I understood is a conveyor passing from production area to storage area via antibiotic lab (testing?). There are openings between lab/production area and lab/warehouse.

If you maintain 150 fpm through both the openings, you can restrict contamination. You may need to go for HEPA in the exhaust if your antibiotic lab is negative with respect to airlock.

 

[berkshire]

Do you have to have access to the conveyor in the lab? If not put the thing in a sealed tunnel.
B.E.

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[Buildtech2]

Quark
You understood it correctly. I have attached sketch for your further review advise. Can I have any reference for maintaining 150 fpm through both the conveyor openings for restricting the contaminants. I think hepa filter is not required for exhausting air from an antibiotic to outside as it is not so hazardous. The peoples are already working in the lab without any special precaution such as mask.

 

[lukaiENG]

you could also look at adding UV lighting over the conveyor at the wall between the air lock and the main corridor. this would at best sterilize any air coming into the airlock, at worst add another layer of protection.
I'm no expert in sterilization of airstreams, maybe there are more suitable products. Electrostatic etc.

I agree with quarks comment that maintaining a velocity through the openings is a solid approach. Think about it from a pressure perspective. if you need to maintain say 0.05" SP across the openings, then work out the free area and pressure drop. You also have to figure in the area of the one of the doors into your airflow rate - you may need to control the fan based on differential pressure.

 

[IRstuff]

Why not just provide an even lower pressure plenum that would suck air from both sides?

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[quark]

We have direct reference for 12.5 Pa or 0.05" WC pressure difference for controlling contamination, as suggested by lukaiENG, and not with respect to velocity. However, when you have one common area with different DPs on two sides, controlling pressure is a bit difficult.

Bio safety cabinets and fumehoods are operated with 0.5 m/s open sash velocity, to minimize operator exposure. Isolator glove breach velocity is about 0.7 to 0.75 m/s. These are established values by surrogate testing. Another point is, Munter recommends 150 fpm velocity across openings to minimise water vapour diffusion.

As you mentioned that the lab is sterile one, I presume it to be of Class B. Conveyor movement generates lot of particles. You should be careful.

 

[Drazen]

you need to make air balance sheets including all neighbouring spaces.

 

[Buildtech2]

Drazen,

Noted with thanks.

 

[Buildtech2]

Our client has requested to provide an airlock between an antibiotic lab and link bridge.There will be two openings in the air lock for the conveyor and the commodity. One opening is between the antibiotic lab and air lock and another opening will be between an air lock and the link bridge. The required opening in the for the conveyor and the commodity is 995 mm x 810 mm
3.26 ft x 2.65 ft = 8.63 ft² = 0.801 m². As per client, -4 pa to be maintained in the air lock.

The required air will be exhasuted from the air lock to create -4pa differential pressure between the air lock and the link bridge as per equation Q = 2610 x A x (DP)1/2 and the equvalent amount of pre-cooldedfresh air will be provided in the link bridge.

Since antibiotic lab is already negatively pressurized with respect to the link bridge, it was assumed that air will only be drawn into the air lock through the conveyor opening between the link bridge and the air lock.
Based on calculations, the required air flow to be exhasuted from an air lock is 3100 cfm and equivalent amount of pre-cooled fresh air to be provided in the link bridge.

Appreciate, if anybody can provide valuable input on this.

 

[lukaiENG]

I wonder if you are looking at this the wrong way. would it not be a better solution to positively pressurize the air lock with lab-grade air and have air pressurizing out of the air lock both into the lab and into the link bridge?
This air could come from your lab ventilation system

 

[Buildtech2]

Thanks LukaiENG. I was also having the same opinion. The air lock to be relocated in the middle of the link bridge to avoid such problems but exhaust air flow calculations from an air lock to be verified as per above equation. 3100 cfm will be adequate to maintain -4pa across the air lock as per given conveyor openings? Please advise.

 

[lukaiENG]

it looks like you're using an appropriate formula though this isn't something I calculate regularly.
Similar topics have been discussed before:

http://www.eng-tips.com/viewthread.cfm?qid=43928

(this thread also references older threads)

 

[chicopee]

Beside UV as mentioned above research out ionization equipment for the air lock