  Experimental conditions at the HERA-B experiment impose very strong
requirements for gaseous detectors. The charged particle fluxes through the
HERA-B tracking system, varying with the radial distance R from the beam line,
are about $2 \times 10^{7}/R^{2}$ particles per second, and comparable to those
that will be encountered by LHC experiments. The severe radiation environment
of the HERA-B experiment leads to a maximum charge deposit on a wire, within
the muon detector, of 200 mC/cm per year. We report recent results of aging
studies performed by irradiating proportional wire chambers filled with
$Ar/CF_4/CH_4$ (74:20:6), $Ar/CF_4/CH_4$ (67:30:3), $Ar/CF_4/CO_2$ (65:30:5),
$Ar/CF_4$ (70:30), $CF_4/CH_4$ (90:10), $CF_4/CH_4$ (80:20) mixtures in a three
different experimental setups. The size of the irradiation zone varied in the
tests from 1 cm up to 500 cm. Our experience shows that the aging rate depends
not only on the total collected charge, but, in addition, on the mode of
operation and area of irradiation. The possible application of these results to
the construction of a large area gaseous detectors for operation in high rate
environments is presented.
