Airman 1st Class Robert Milburn uses a bristle brush to clean electrodes. U.S. Air Force Airman 1st Class Robert Milburn, an aerospace ground equipment apprentice with the 28th Maintenance Squadron, uses a bristle brush to clean electrodes from a fuel-burning assembly at Ellsworth Air Force Base, S.D., on March 27, 2009. The fuel-burning assembly is used to ignite the heat exchanger of new-generation heaters. Maintenance personnel use the heaters to stay warm on the flight line. SHARE: Download: Full Size (0.06 MB) Credit: VIRIN: 445499-Y-PYV80-409.jpg Photo Gallery