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Reports until 21:05, Wednesday 28 December 2011
LHO General
robert.schofield@LIGO.ORG - posted 21:05, Wednesday 28 December 2011 (1958)
Particle levels in cleaned BSC8 down by about 10 from 2007, Y-manifold unchanged

Summary: I measured particle counts in the Y-manifold and newly-cleaned BSC8, and compared them to levels I measured in 2007. High-activity particulate levels (>0.5um) were about 100/ft^3 in BSC8, down by a factor of  about 10 from 2007, and about  1000/ft^3 in the manifold, unchanged from 2007. After cessation of activity, manifold particulate levels dropped by a factor of 2 approximately every 7 minutes. To prevent activity in the manifolds from contaminating the clean chambers, I suggest using a dam to separate clean and unclean regions and/or selecting purge air ports so that the air flows from  clean BSCs to unclean manifolds.  


In preparation for installing the arm cavity and cryopump baffles, which will require work in the un-cleaned manifolds, I compared in-chamber particle levels for activity in the manifold to levels for activity in BSC8. I did not want my manifold measurements to contaminate clean BSC8, which has the ITM and FM, so I ensured that purge air was flowing out of the Y-manifold where it is open at the gate valve, and my simulated activity took place between the purge air port and the opening at the gate valve. The manifold measurements were made after vacuuming of the manifold. My measurements in BSC8 took place while Travis was unlocking and preparing the quad, which involved a lot of movement and sliding on the chamber floor. 

I took several tens of 1 liter measurements, which are summarized here and compared to measurements taken at the same locations in 2007, here, before the cleaning of BSC8.

                                                          Counts per cubic foot >0.5 micrometers in diameter

                                                       Y-Manifold                              BSC 8

Activity level                             2007        2011                     2007       2011

High (sliding, walking)                         ~1000     ~1000                   ~1000      ~100

Low (careful movement)                                      ~200                     ~150        ~25

The cleaning of BSC8 appears to have reduced particulate levels during heavy work by about an order of magnitude. I also experimented with brushing the chamber wall with my bunny suit. In the manifold I got large pulses of counts (>1000/ft^3) as particles came off the wall, but in BSC8 I got no evident increase in particle levels (~25/ft^3). 

Thus the cleaning of BSC8 was successful but, if we are not careful, the particle load from activities in the manifold may swamp any gains from cleaning BSC8. For the part of the arm cavity baffle installation procedure that requires moving in equipment through the manifold, we plan to install the dam between the manifold and BSC8, with the aperture in the dam mostly blocked with foil in order to reduce the quantity of particles that enter BSC8 from the manifold.

After settling (counts dropped by a factor of 2 in about 7 minutes) we will remove the dam and retrieve the staged equipment from the manifold while trying to minimize scuffing the floor and brushing the walls. I find that I can walk in the manifold and maintain ~100/ft^3 level by not sliding my feet and not brushing the walls.

I also suggest that, where possible, the purge air be set up so that the flow is from clean chambers into the dirty manifolds. This is currently not the case at BSC8 and would require switching purge air ports.


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