After an installation is commissioned and the “as-built” drawings are issued, no unauthorised modifications may be made to the system. Any changes found necessary must be approved (and the relevant documentation issued) by the engineering and design team responsible, before they are implemented.
Testing in the presence of flammable gases requires careful consideration of the circuits to be tested. Test and measuring instruments used are to be approved for use in IS circuits, and care must be taken to prevent damage by improper use of tools etc. Safety barriers must never be “bridged” by test instruments.
A zener barrier may be tested to check if the fuse has blown by measuring resistance between the IS and non-IS terminals after the barrier has been disconnected from the IS circuit.
The manufacturer’s documentation must be studied before any work is started.
Live maintenance work on I.S installations in the hazardous area should be limited to:-
- Disconnection of and removal or replacement of equipment and wiring which are parts of the IS circuit
- Adjustment any controls necessary for calibration of the IS equipment
- Removal and replacement of any plug-in components or assemblies
- Taking electrical measurement using the specific type of test instrument specified in the documentation.
- Other maintenance activities specifically permitted in the documentation.
Live maintenance work on I.S circuits / equipment located in a non-hazardous area
- Maintenance work on associated electrical apparatus and parts of I.S circuits shall be carried out only if the electrical apparatus or part of a circuit is disconnected from the part of circuit located in a hazardous area.
- Safety barrier earth connections shall not be removed without first disconnecting the hazardous area circuits except where duplicate earth connections are provided.
Live maintenance of associated apparatus or on parts of an IS system mounted in the safe area should only be done when the location of the remote equipment has been certified gas-free, or the remote equipment or part of the circuit is has been disconnected from the safe area equipment under test.
