Certification
Benefits of Using Safety-Certified Products
Selecting a device for use in a Safety Instrumented SystemThe IEC 61511 / ISA 84 international safety standard defines the requirements for end users and engineering companies to follow when selecting components and subsystems for use in a safety instrumented system (SIS). There are two approaches to demonstrating suitability for use:
- Product was designed and developed in accordance with IEC 61508
- Product has completed a “Prior Use” Justification
Certification to IEC 61508
The IEC 61508 standard defines the requirements for suppliers to follow during product development to ensure that their products have a high level of resistance to random and systematic failures. Compliance is demonstrated by third party certification agencies such as exida assessing and certifying that a product has been designed and developed in accordance with the standard. Detailed Comparison of Prior Use to IEC 61508 Certification
Prior Use Justification
This is an alternative method for showing that a component or subsystem already in operation is suitable for use. The user must put in place a rigorous process for tracking and documenting operating experience to gather evidence of suitability. The recording of operating hours and analysis of all repairs and failures must be done to justify that the device has the necessary reliability to be used in the intended application. Because of the additional effort, cost, and risk with “self certification”, most end users prefer to use certified devices.Detailed Comparison of Prior Use to IEC 61508 Certification
Benefits of using devices certified to IEC 61508
- Lower lifecycle costs -
- No need to justify use of device by costly “prior use” analysis and tracking of installed devices
- Reduces effort, cost for safety system design (SIL Verification)
- Independent, 3rd Party assessment improves quality & reliability
- Easier compliance with international standards
- Reduces risk (accidents) and liability
- Helps ensure SIS is not overdesigned ($$) or under-designed (↑ risk)
Product reliability data for SIL Verification
As part of exida’s 61508 certification process, the product reliability data (failure rates, diagnostic coverage) is determined from a Failure Modes, Effects, and Diagnostics Analysis (or FMEDA).This reliability data is needed by safety lifecycle tools (it is preloaded into exSILentia) to help SIS designers verify that the safety integrity level provides the required level of risk reduction.