Testing considerations of SIF should be included in most of the Safety Lifecycle steps described in ANSI/ISA-84.01-1996. Testing frequency is a part of the determination of Safety Integrity Level (SIL) for the SIF. Provision for conducting tests must be included in the selection of equipment and design of the SIF and the Pre-Startup Acceptance Test (PSAT) is an integral part of ensuring the SIF will provide the risk reduction necessary. When modifications are made to SIF, testing can validate that appropriate SIF action will still take place.

This technical report is an informative document providing guidance on performing testing of SIF components and systems that will help achieve full safety benefits of the SIF in the most cost-effective way. Both manual and automated techniques are presented for off-line and on-line testing of SIF and the benefits of each technique described. Existing techniques and proposed new techniques will be described. Utilizing the techniques described in conjunction with an overall safety management program will allow users to meet the testing requirements of ANSI/ISA-84.01-1996 and dIEC 61511. Techniques are described for testing all elements of the SIF including field sensors, final control elements, logic solvers (signal conversion modules included), Human Machine Interface (HMI), communication links with other systems, user application software, and other required auxiliaries such as power. Suggested inspection techniques for regular observation of equipment and components to detect potential problems are also presented.

The techniques described can also be used for testing burner management systems in conjunction with the NFPA 85 code.

These techniques are illustrated by the examples given in Annexes A-MM. Each Annex is an example of how one company might apply a given technique, and is not intended to represent a consensus solution within the process industry.

Purpose

Systematic testing of each Safety Instrumented Function (SIF) is required to ensure that dangerous unrevealed failures have not occurred that could render the SIF unable to perform the function for which it was provided. This testing ensures that all operational functions of the SIF are evaluated on a periodic schedule in accordance with the safety integrity requirement of the SIF. Many processes have operating cycles that are longer than the period between testing required achieving the safety integrity. Thus performing the required off-line testing necessitates shutting down the process. This is costly and puts unnecessary strain on equipment and necessitates going through shutdown and startup (which are usually the most dangerous periods of a process lifecycle) again. Therefore, the ability to perform testing while the process remains in operation is desirable.

There are also different ideas on what constitutes an acceptable test for various components of SIF. Whether the test is performed off-line, with the process down, or on-line with the process in operation, there are methods for performing the testing that ensure a high degree of detection of failures that might have occurred. Guidance is needed in the selection of these testing methods for both off-line and on-line situations.

There is also benefit in performing inspection activities on SIS equipment during normal operation of the process to detect any potential problem creating situations that might be developing. Guidance in what to look for, how often to inspect, and what to do when a condition is observed that could lead to a failure will enhance the safety integrity of the SIF.