D0 Clean Room ODH Analysis

Table A shows the steady state situation. One ofthe two dewars would be supplying purge gas at (a maximum of) 20 scfm, which would leak: into the room through the welding orifice. Instantaneous uniform diffusion and exhaust are assumed. Note the probability is 1 for the 20 scfm leak since it is a planned occurrence. Table B is the same situation in the event of a power failure, estimated for twice a year (2.29 x 10{sup -4} fails/hour). This assumes that the exhaust is shut down, and the dewars are not turned off. This would require the minimum exhaust to be the same as the leak: (as an approximation). These results, however, would only be valid for an infinite supply of the purge gas, and for an exceedingly long power failure. Since the supply of LAr would only last a day at most, and the power failure would not last for weeks, this result has no real significance. In fact, the time constant for the ODH equation in this case is 5717 minutes, which means it would take 20 days for all the oxygen to be displaced. A worst case scenario would be a full dewar completely emptying into the clean room in a short time relative to the ventilation rate, but slow enough for uniform dispersion. We can do a leak/exhaust independent (ventilation rate=O) analysis. This also assumes instantaneous and uniform mixing. This suggests that even with a complete dewar failure, the oxygen content would not decrease to a safety hazard. The probability ofa simultaneous, catastrophic. dewar failure would be so low as to offset the consequences as insIgnificant, and even so. those consequences would be only a slight oxygen deficiency (17.5% 0{sub 2}) These same arguments could be followed for LN2 dewarst and would have the same results except for the last case. Since nitrogen would not expand as much, the displaced volume would only be 3945 cf, and the resulting displacement would lower the oxygen content to 19.55%. In fact, emptying both dewars would only decrease the oxygen content to 18.1%. None of these analyses suggest a safety hazard in any manner, so no ODH equipment need be present