Mechanical hold-open devices and hold-open arms on door closers should be avoided. Fusible link equipped closers with a hold-open feature are available, but the fusible linkages will not function quickly enough to allow the door to act as a protective barrier to save human lives. Tests and investigations have proven that smoke and toxic gases are the main cause of death in tragic fires. Doors held open by electromagnetic release devices are the only ones which will close quickly enough to prevent the passage of the toxic gases and smoke. These devices are activated by electronic detectors that sense smoke and/or the products of combustion.