Recirculating air streams

The recirculating air stream is considered an integral portion of the life safety system therefore, in a hazardous occupancy cleanroom (such as a semiconductor wafer fab), the system should not be automatically shut down by the smoke detection system. In lieu of automatic shutdown, a manually operated remote switch is to be provided at an approved location outside the fabrication area (UBC 1202.2.5). Since such a detection could happen at any time, our recommendation for the location of the switch is in a continually occupied but relatively secure spot, such as the nearest Emergency Control Station (ECS). UBC 1202.2.5 also dictates that the return air system of one hazardous cleanroom area shall not be connected to another eleamoom oeeupancy. 

Difficulty was encountered during some of the early test runs because the liquid-oxygen—nitrogen mixture did not vaporize immediately when introduced into the cabin. It dripped off of the valve and formed in pools on the floor. This resulted in loss of control over the chamber environment. This difficulty was remedied by placing a drilled baffle in the recirculated air stream for the cryogenic liquid to impinge upon. This worked very satisfactorily. However, an atomized supply would probably be preferable. 

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