Guidelines for controlling hazardous energy during maintenance and service operations of machines, processes, or systems are provided. The guidelines are intended to protect workers from injury by the unexpected and unrestricted release of energy due to pressure, gravity, springs, electrical release, and thermal energy resulting from high or low temperatures. Accident reports are analyzed and categorized by fire, explosion, impact, fall, caught between, or others. The major identified hazard causes include maintenance activities initiated without deactivation of the equipment or system; inadequate energy blockage or isolation; failure to dissipate residual energy; and accidental activation of energy. A systems analysis approach is used to provide a logical system for performing maintenance and servicing activities safely. The logic tree provides a step by step diagram for controlling hazardous energy that should be used in the formulation of specific maintenance and servicing procedures. The authors indicate that existing Federal and State safety regulations of energy control during maintenance, with the exception of Michigan and California, are inconsistent. Most of these regulations use the concept of power off to prevent injuries and do not provide guidance on how to discern when to apply power locks, tags, or a combination of locks and tags.