In ISA‑88 terminology, a procedure is the structured, ordered set of actions that defines how a batch is executed. It is part of the ISA‑88 batch control model, not a single document or a generic “standard operating procedure.”
Where “procedure” sits in the ISA‑88 model
ISA‑88 defines a hierarchy for batch control activities:
- Recipe > overall definition of how to make a product (ingredients, timing, equipment requirements, etc.).
- Procedure > top-level sequence of steps for executing that recipe.
- Unit procedure > subset of the procedure run on a specific unit (for example, Reactor 101 charge and react).
- Operation > logical step within a unit procedure (for example, heat to setpoint, agitate, hold).
- Phase > lowest-level actions implemented in the control system (for example, open valve, start agitator, ramp temperature).
In practice, the ISA‑88 procedure is the layer that organizes unit procedures, operations, and phases into a coherent batch sequence that automation and operators can execute and track.
What an ISA‑88 procedure actually does
An ISA‑88 procedure:
- Defines the execution order of unit procedures and operations for a batch.
- Captures branching and conditions (for example, if temperature not reached in X minutes, raise alarm and hold at step Y).
- Links recipe logic to equipment capabilities through the equipment model.
- Provides a structure for traceability so you can reconstruct what happened in a batch at the level of procedure, unit procedure, operation, and phase.
The procedure is typically implemented in a batch control system (DCS, PLC/SCADA with batch add‑ons, or a batch engine) and may be referenced by higher-level MES workflows. It is not by itself a regulatory filing, but it contributes to how your manufacturing process is executed, monitored, and recorded.
Common misconceptions and constraints
- Not the same as an SOP: An SOP may describe similar steps in narrative form, but the ISA‑88 procedure is a control model used by automation. In regulated plants you usually have to keep both aligned under change control.
- Not a compliance guarantee: Using ISA‑88 structure does not imply compliance. You still need validation, documented requirements, and controlled changes.
- Highly implementation‑dependent: How “procedure” is represented, edited, and executed depends on your batch engine, control platform, and how strictly your integrator followed ISA‑88.
How ISA‑88 procedures coexist with existing systems
In most brownfield plants, ISA‑88 concepts are layered onto legacy control and MES/ERP systems instead of replacing them:
- Control system level: The phases and operations are embedded in the DCS/PLC code, often with an ISA‑88-like structure but not always fully compliant.
- Batch engine: The procedure and unit procedures often live in a batch management module that orchestrates equipment phases and records batch events.
- MES/EBR/QMS: Higher-level electronic batch records and workflow systems reference the procedure steps, but also add checks, approvals, and documentation steps that are not directly part of ISA‑88.
Full replacement of legacy batch logic with a new ISA‑88 implementation can be risky in regulated, long‑lifecycle environments because it triggers significant re‑qualification, extensive downtime, and complex integration work. Many plants instead incrementally refactor existing recipes into ISA‑88 structures during control system upgrades or capacity expansions.
Implications for regulated and validated environments
When you use ISA‑88 procedures in regulated industries (for example, pharma, biotech, some specialty chemicals):
- Traceability: The procedure hierarchy helps you tie batch events, alarms, and setpoint changes to specific steps, which improves investigation and reporting.
- Change control: Any change to procedure logic (sequence, limits, branching) typically requires impact assessment, documented testing, and sometimes re‑validation.
- Recipe versions: Multiple versions of a procedure may coexist for different markets or process revisions. Managing which version was used for which batch is essential.
- Integration quality: The value of ISA‑88 structure is only realized if MES, historians, and reporting tools correctly capture the procedure hierarchy and identifiers.
In summary, the ISA‑88 procedure is the formalized, hierarchical description of how a batch is executed within the ISA‑88 framework, linking recipe logic to real equipment and providing structure for automation, traceability, and controlled change. Its effectiveness depends heavily on your specific control platform, integration approach, and validation practices.
