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--obsolete-- Safety Interlock Defeats

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"The attached note summarizes a discussion Andy and I had regarding interlock defeats." - John Drozdoff

By John Drozdoff and Andy Hurst, Feb. 24, 2006


We have reviewed the ISAC Operators' Manual Safety Defeats section 2.8 and feel some items should be restated in light of both recent system explansion and past experience.

  • A good definition of an interlock defeat is the following: "A system interlock is said to be defeated when some action is taken to change its functionality so that it no longer provides protection as designed." This definition takes into account the raising of warn and trip setpoints and the application of software overrides, as well as the simulation of signals that are missing for some reason. All of these should be considered as safety defeats and must be implemented in conformance with section 2.8.
  • One of the procedures in section 2.8.3 states that "Approval signatures must appear on the (defeats) form." A signature can be very difficult to obtain in practice, as many situations arise outside of normal working hours. The name of the expert who was consulted can be an acceptable substitute.
  • A proposal to allow Operators to make specific safety defeats without approval from Safety was reviewed and approved last year. The specific defeats are: 
    1. The temporary raising of Target Maintenance Hall detector warn and trip setpoints to silence alarms during planned target movements.
    2. The temporary defeating of a failed detector in an area that is not receiving any beam capable of generating any radiation.
  • The Safety Defeats book should be reviewed once evert shift to ensure that defeats have been removed as soon as possible. One typical safety defeat is the raising of detector warn and trip setpoints during tests of unusually high beam intensity. Operators should restore default warn and trip setpoints when normal beam intensity resumes.
Section 2.8 of the ISAC Operators' Manual

will be appropriately revised at some future date.

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