Currently under construction at Brookhaven National Laboratory (BNL) is a large 3.8 km in circumference collider called the Relativistic Heavy Ion Collider (RHIC). The collider is capable of creating thousands of head-on collisions between beams of heavy ions, e.g., gold, or polarized protons traveling at nearly the speed of light Four experiments built along RHIC’s underground ring will measure the particles unleashed when the beams collide. This study deals with the PHENIX Detector which roughly fills an Experimental Hall with a floor area of 18.6 m by 15.8 m and a height of 14.3 m. The RHIC tunnel connects to the Experimental Hall through two opposite walls. The large tunnel openings are almost completely obstructed by massive steel plates which are part of the PHENIX Muon detector system. The Experimental Hall walls are all fixed except for one which is constructed from 1.7 m thick concrete blocks covering an opening which is 18 m wide by 14.0 m high. This block wall has a plug door which is designed to be unstacked so that large PHENIX detector systems can be transferred from the Experimental Hall into the adjacent Assembly Hall when required.

The detector consists of several systems, each with its own role in detecting subatomic particles. Combustible gases such as ethane, isobutane, and methane are used in several of the detector systems. In particular, one of the systems called the Ring Imaging Cherenkov Detector (RICH) uses 80 m3 of pure ethane in two welded aluminum frames each with two large 0.127 mm thick aluminized KAPTON windows. The ethane gas is maintained at a pressure of a fraction of an inch of water above the ambient pressure. The work reported here deals with a safety analysis for a hypothetical accident scenario whereby the RICH windows are damaged and all the ethane inventory is released into the Experimental Hall, mixed with the ambient air and ignited. The objective of the analysis was to determine the scope of damage to the experiment and danger to personnel under various accident scenarios involving the extent of ethane gas release, the degree of mixing with ambient air and the mode of combustion. If all the ethane is assumed to be released and allowed to mix with the entire volume of air contained within the Experimental Hall, the calculations show that ignition of this mixture would not result in the collapse of the block wall.

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