Safety-related control systems categories

There is possibility of confusion regarding use of two standards viz ISO 13489. lEC 62061. Normally when medium other than electrical system, ISO 13489 may be more appropriate. Whereas for customer demand for demonstrating safety lEC 62061 may appropriate. Fot safety-related control systems, standard components can be used as it is allowed as pet standard also. However, safety components offer the advantage of reducing workload as the safety-oriented assessment, and analysis of the components used, is carried out by the producer of the safety components. For functional safety, the systematic integrity of components is taken into account, in addition to the use of a suitable category, the implementation of necessary fault detection and the... 

Title Safety of Machinery - Safety Related Parts of Control Systems Description Parts of machinery control systems are fi equently assigned to perform safety functions. Part 1 of this standard provides safety requirements and guidance on the general principles of safety related parts of control systems. Part 2 specifies the validation process including both analysis and testing for the safety functions and categories for the safety-related control systems. 

These standards closely mirror the requirements of IEC80001 but require a proportionate set of controls reflecting the less critical nature of advisoiy or safety related software systems. There is no regulatory requirement for this class of systems. All assurance is conducted by accreditation of supplier process and subsequent inspection of safety deliverables. In this respect it was hoped to avoid the burdens of a compliance scheme such as the medical devices directive (which in its current form is felt by suppliers to be burdensome and overly bureaucratic for this category of software). 

It should be noted that the eategories are not a measure of the risk on the maehine, as is commonly assumed. They are simply a means of classifying the required safety performanee of the safety-related parts of the control system on a machine. Indeed, a single eontrol system may eontain subsystems that have differing categories and which are implemented in different technologies. 

The WSRC Reactor Technology Department has Issued a list of systems defined as "important to safety." WSRC-TR-90-42-133, "Uniform Listing of Reactor Systems, Acronyms, and Safety Systems" (Reference 12) defines the criteria for creating this list and includes the list of systems and equipment evaluated as important to safety. This list contains all the systems identified as safety-related in Section 5.6 of the SER. "Work Control Manual," RD-3.1 has established criteria and specific minimum requirements for maintenance activities on equipment or systems that are considered important to safety. These requirements include the use of Category 1 or 2 procedures or work instructions for the performance of the maintenance activities and the approval of the work package by Reactor Engineering and QA. 

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