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Toxic gas alarm prompts Building 13 evacuation

Building 13 was evacuated Saturday afternoon for about three hours after a 10-year-old environmental exhaust scrubber in a laboratory ruptured and triggered a toxic gas alarm. No one was in the lab at the time.

The alarm was set off by the escape of a small amount of silane gas, which burns immediately in contact with air. The room alarm was triggered but then showed no toxic level because the silane had burned up, William McShea of the Safety Office said.

Students working in an adjacent lab on the fifth floor said they "heard a pop" and looked through the glass window into the chemical vapor deposition lab in Rm 13-5137. They saw white smoke, immediately triggered the fire alarm and exited the building shortly after 2:30pm.

The Cambridge Fire Department responded promptly but no one was able to enter the room for about two hours because an environmental monitor, set off by the flash of silane, indicated a level of about 0.15 parts per million (ppm) of silane. The head of the lab, Associate Professor Eugene Fitzgerald of Materials Science and Engineering, said that 5 parts per million is considered a safe level, but they routinely evacuate the lab if lower concentrations are detected, since the normal condition is no detectable gas in the lab.

Professor Fitzgerald said the lab's activities focus on the current limitations of electronic materials, especially limitations created by imperfections in materials such as point, line and planar defects.

The chemical vapor deposition laboratory uses silane to deposit silicon-based semiconductor layers on top of a 4-inch wafer of silicon substrate. Those materials are then used to fabricate electronic devices such as those used in Internet switch applications and other uses.

A version of this article appeared in MIT Tech Talk on November 24, 1999.

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