Functional Safety 2016

November, 2016 - London

Page 13 of 17

Equipment

Proof Test Method (brief description)

(%)

setpoint) of the initiator. Or push the test button to test only the

FE and not the mechanical initiator. For verification of the

mechanical initiator refer to the specific Installation, Operation

and Maintenance Instructions and Safety Manual. If other

sensors monitor the system safety, these must be tested.

4. Check each time that the valve is completely closed or opened

when required. If possible, drain the downstream part of the line

and verify that the valve does not leak when closed.

Even when following the vendor requirements stipulated within the equipment safety manuals, it

can be seen that none of the vendors claim to have 100% proof test coverage. It is also

important to note that in each of the Safety Manual requirements the vendor makes the

assumption that the proof test is carried out by a competent person. They take no further claim

for systematic capability of the end-user.

Taking the assumption that so far as is reasonably practicable the systematic requirements for

the proof test coverage have been adopted, the table below illustrates how to incorporate the

prescribed proof test coverage factors into the calculations and demonstrates how the C

and

corrected PFD

AVG

impacts on the SIS risk reduction requirements.

Note:

Systematic Requirements for the proof test coverage are that a competent person has accurately specified

the SIS, a competent engineer has design the system to permit all requirements of the proof test to be conducted,

a competent person has developed the proof test incorporating all the above requirements from the relevant safety

manual, a competent person has conducted the proof test and a second competent person verifying the proof test

has been conducted as prescribed.