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OPERA is part of the CNGS project and it is an experiment dedicated to the observation of long-baseline [v.sub.[mu]], into [v.sub.[tau]] oscillations through [tau] appearance. Resistive Plate Chambers (RPCs) with bakelite electrodes are used to instrument the 2 cm gaps between the magnetized iron slabs of the two spectrometers. The RPC installation ended in may 2004 on the first spectrometer and in march 2005 on the second one. Before the installation, every RPC is subjected to a complete test chain in order to reject the poorer quality detectors. The tests are performed in dedicated facilities to ensure the proper RPC gluing, to measure its electrical properties and to verify the response to cosmic rays and the intrinsic noise levels. We have also tested the long term stability of real size OPERA RPC prototypes operated at cosmic ray fluxes for more than one year. On small size prototypes we are performing studies on the gas mixtures in order to reduce the total charge released in the gas for each detector count. The validation of the installed RPCs has been performed with pure nitrogen. A small part of them has been also tested with the gas mixture Ar/[C.sub.2][H.sub.2][F.sub.4]/i - [C.sub.4][H.sub.10]/S[F.sub.6] = 75.4/20/4/0.6. Index Terms--OPERA, Resistive Plate Chambers (RPCs).

Resistive plate chambers (RPC) are widely used as active elements in particle physics detectors. A deterioration of RPC performance with time has been observed in several experiments, after operation at high temperature or with water contamination in the gas mixture, both for detectors with bakelite electrodes and for the ones with float-glass electrodes. We have developed a kind of RPCs suitable for large scale industrial production. Float-glass is employed as electrode material, and the screen-printing technique is used to apply the resistive coating on the electrodes. A dedicated intensive measurement program on these detectors has been carried out, to assess their long-term behavior and aging properties under different operational conditions. Index Terms--Aging, glass, resistive plate chambers (RPCs).