  The Daya Bay Antineutrino Detector gas system is designed to protect the
liquid scintillator targets of the antineutrino detectors against degradation
and contamination from exposure to ambient laboratory air. The gas system is
also used to monitor the leak tightness of the antineutrino detector assembly.
The cover gas system constantly flushes the gas volumes above the liquid
scintillator with dry nitrogen to minimize oxidation of the scintillator over
the five year lifetime of the experiment. This constant flush also prevents the
infiltration of radon or other contaminants into these detecting liquids
keeping the internal backgrounds low. Since the Daya Bay antineutrino detectors
are immersed in the large water pools of the muon veto system, other gas
volumes are needed to protect vital detector cables or gas lines. These volumes
are also purged with dry gas. Return gas is monitored for oxygen content and
humidity to provide early warning of potentially damaging leaks. The design and
performance of the Daya Bay Antineutrino Detector gas system is described.
