The barrel hadronic calorimeter has an inner radius of 3.39 m and outer radius 4.39 m, and is cylindrical in shape. There are eight layers of 100 mm thick iron and these are separated by nine layers of detector. The detectors consist of limited streamer mode tubes with wires parallel to the beam axis. The tubes are filled with 75% isobutane and 25% argon. The iron layers are separated by 25 mm.