Disclosed herein are a system, method, and apparatus for arresting flames in an air return line. The apparatus includes a flame barrier containing one or more metal mesh layers and configured to permit airflow there through while preventing flame break-through. The flame barrier can also have or be connected to one or more temperature or pressure sensors configured to detect blockage of airflow through the flame barrier and to detect damage to the flame barrier. The apparatus can also include additional temperature or pressure sensors for detecting the propagation of deflagration in the air return line.