The muon chambers, like many of the other detectors, are split into a barrel region and an endcap region. They give coverage of 93% of the solid angle, and are designed to detect muons. Muons are highly penetrating and will pass through the ECAL and HCAL. Hadrons also usually pass through ECAL, but almost never through HCAL to reach the muon chambers. The probability of a pion reaching the muon chambers is less than 0.1%, so misidentification within the muon chambers is highly unlikely.