a fault protection circuit for a respiratory conduit heater element in a respirator humidification system is disclosed . the circuit includes a spark detector as well as overcurrent detector . several variations are included for the spark detector including a two winding transformer , a center tapped two winding transformer ), and a high pass filtered inductor . a semiconductor switching configuration is also disclosed . once the protection circuit detects a change in current over a certain level , or the average level raises above a threshold , then the current in the heater element is interrupted for a preset period .