15 July 2008

Essential tool in automation: Safety standards

Early in the computer revolution, engineering companies started developing their own instrument engineering automation tools to manage and control instrument data and to reduce hours by automating repetitive tasks, standardizing deliverables, and to help meet documentation requirements for ISO 9000 certification.

Companies soon realized instrument automation systems would improve plant safety by identifying data integrity issues and potential problems, reduce costs, and improve productivity of plant personnel with real-time data.

Automation system databases would also support regulatory compliance (OSHA 1910.119 and 21 CFR 11) with change management, controlled access, and electronic record-keeping. Use of databases and real-time data acquisition improved return on assets by lowering costs associated with down time and provided facilities for quicker disaster recovery.

Deliverables from the instrument automation tools provided intuitive visualizations to operators, and the databases became functional knowledge management systems that captured complex configurations and operation strategies. As we incorporated safety systems into operation strategies, we used the same systems for plant operations and expected operator interfaces to integrate and display the plant control system and the safety instrumented system (SIS) statuses.

Because the ISA 84.01/IEC 61511 standards for defining safety networks are fairly new, the industry is lagging behind in providing the special data fields required by safety DCS, PLC, and wiring networks. Safety networks requiring special documentation in instrument engineering automation systems include emergency shutdown systems, burner management systems, fire and gas systems, and SIS or interlock systems.

In 1998, the International Electrotechnical Commission (IEC) developed IEC 61511 - "Functional safety instrumented systems for the process industry sector." Six years later, the ISA84 committee adopted the IEC 61511 standard for use in the U.S. and created the ANSI/ISA 84.00.01-2004 or ISA 84.01/IEC 61511. These standards called for SIS designs that automatically responded to potentially dangerous process conditions and took preprogrammed action to mitigate or avoid a dangerous condition. In addition, the safety-related portion of the plant control systems configuration must remain in place for the lifecycle of the plant and should remain separate from the non-safety-related portion of the configuration. You must also maintain the SIS for the complete lifecycle of the process.

A 2005 publication of IEC 61508 defines a set of standards for functional safety of electrical or programmable electronic safety-related systems equipment. By complying with this standard and switching from hardwired safety products to internationally certified, automated safety solutions, manufacturers enjoyed lower costs, heightened flexibility, and reduced chances for operator error. Instrument engineering automation systems designed to document the plant control systems and distributed control systems now must handle SIS data requirements.

Most instrument engineering automation systems document and produce instrument indexes, instrument spec sheets, field wiring network documents, and loop diagrams for plant control systems. Additional functionality provides concurrent engineering, work sharing, and system integration. Because the instrument system field wiring generally ended at the DCS I/O, it was necessary to integrate the plant control systems to multiple DCS vendors. Control elements also became part of most engineering automation systems.

You can use an instrument engineering automation system to generate SIS reports, construction drawings, and other deliverables. You can also generate construction wiring diagrams and schedules the same as other non-safety instrument system documents.

Most instrument engineering automation tools have facilities to create CAD documents from data contained in the wiring database. Using the CAD generation feature, you can create SIS loop diagrams and PLC ladder diagrams for construction and commissioning. You can use automated report generation to produce SIS I/O reports and alarm summaries.

You cannot easily create all deliverables with the instrument engineering automation system because they are designed to handle simple, repetitive tasks such as standard two wire loop diagrams and junction box wiring diagrams. Complex loops containing series or parallel-wired devices can require a lot of time to create with automatic generation.

When specifying safety devices, spec sheets (data sheets) created in the automated instrument engineering system will have additional information not normally provided for with non-safety devices. Most instrument spec sheets in engineering automation systems are configurable to allow you to place additional data on them.

You will need to identify safety standard compliances and test requirements on the spec sheet for proper selection of the instruments. Specify sensors that are proven-in-use or designed per IEC 61508. Include the safety integrity level or certification requirement in the spec. For actuators, define additional options for partial stroke testing devices and trip solenoids with dual coils in the spec sheet. The process data portion of the spec will also indicate safety alarm and trip settings, failure states, and other safety related process conditions.

-John Dressel