predictive maintenance systems and methods are described . a method includes measuring environmental conditions using a plurality of sensors within the ied , processing the environmental measurements to determine long - term exposure factors representing historical operating conditions of the ied , applying a reliability model to the long - term exposure factors , determining a numerical measure of ied life based on the long - term exposure factors and the reliability model , comparing the numerical measure of ied life to preselected boundary values , and signaling if the numerical measure of ied life is outside of the preselected boundary values .