The GIS utilizes trapped key interlocking. Trapped key interlocks are also known as Castell or Kirk key among other names. Trapped key interlocks utilize a series of keys and locks for sequential control of equipment and machinery.
Trapped key systems function by requiring that a key or possibly several keys be used to enter a hazardous area, or before beginning to use equipment that may cause interferences. The only way to obtain the key(s) is by first isolating the source(s) of hazardous energy. This primary key can only be removed after hazardous energy is isolated from the machine. The use of multiple keys ensures that multiple sources of hazardous energy are removed or that a specific sequence of events must happen.
Trapped keys are not a substitute for lockout/tagout.
If a safeguarded area requires full-body access, then a personnel safety key must be obtained prior to entering the safeguarded area. Personnel safety keys are released when the primary key (obtained when isolating hazardous energy) is used to unlock access to the safeguarded area. The personnel safety key must be kept in the control of the person entering the safeguarded area at all times.
Trapped Key Maps
Graphical representations of trapped key sequences.