Editing Kill switch (section)

===Complementary protective measure===
[[File:Homemade Mollyguard.jpg|thumb|An emergency stop button with a custom-made plastic molly guard to prevent it from being pressed accidentally]]
A machinery's emergency stop control is considered a complementary protective measure<ref name="ISO_12100"/> because it is intended to complement the primary safeguarding measures like [[Machine_guarding|fixed guards, movable interlocked guards or safeguarding devices]]. The primary safeguarding measures prevent injury automatically, either by enforcing distance between a hazard and a person, or by eliminating the hazard by stopping hazardous motion or switching off a source of hazardous energy.

By contrast, an emergency stop requires a deliberate action on the part of a person who must first recognize that some hazardous condition is about to arise or is arising, and who then must activate the emergency stop function by pressing the emergency stop button or activating another emergency stop device such as a pull-cord switch.