A fiber monitoring system for detecting the occurrence of a thermal event, especially of a traumatic nature, in optical fibers while transmitting laser beams includes one or more fiber monitoring apparatuses each having a thermal sensing array supported by a holder board of a laminated dielectric material having a row of clips for retaining optical fibers in alignment with thermal sensor devices of the thermal sensing arrays. The thermal sensing arrays also have electrical circuitry elements for electrically interconnecting the thermal sensing devices in series and enabling electrically connecting the thermal sensing arrays with other circuitry to form a thermal interlock circuit for a laser system.