Automated Independent Backup
Chemical processing sometimes poses significant risk to personnel and the community. Some process risks can be significantly reduced through inherently safer design practices. The remaining risk is managed by engineered and administrative safeguards. An independent safety instrumented system (SIS) is installed when it is necessary to override the operation of the process equipment in order to prevent the process hazard from occurring. The SIS must be independent and separate from the control system unless the user intends to design and manage the entire system as an SIS (ANSI/ISA 84.00.01/IEC 61511 Clause 11.2.4).
Legacy control systems are generally not designed to meet SIS requirements. Unfortunately, during the early migration into digital controls, many users implemented their SISs within their process control systems. Many of these users have implemented or intend to implement open systems to support business and plant operations. They do not want to impose SIS design or management restrictions on their control systems. Consequently, many users are looking for an independent back-up system that meets the appropriate safety standards and connects easily to existing plant equipment.