Why batch needs its own standard

Continuous processes (an oil refinery) have stable operating points, well-described by control loops on flows, pressures, temperatures. Batch processes don’t. A pharmaceutical batch evolves through dozens of state changes over hours : weighing, dispensing, heating, holding, reacting, cooling, sampling, transferring, cleaning. Each phase has its own setpoints, its own constraints, its own failure modes.

Before ISA-88 (1995), every batch plant invented its own terminology, its own recipe structure, its own coupling between recipe and equipment. Result: zero portability of recipes between sites, impossible audit trail, costly DCS reconfiguration when equipment changed.

ISA-88 created the shared vocabulary the industry needed. Today, every batch DCS vendor (Emerson DeltaV Batch, Siemens SIMATIC Batch, ABB 800xA Batch, Yokogawa CENTUM Batch, Rockwell FactoryTalk Batch) implements ISA-88. Recipes can be exchanged between sites. New operators learn the same model. Auditors look for the same artifacts.

The two-axis model in plain words

                                   PROCEDURAL MODEL
                                  (the "what to do")
                                          │
       ┌──────────────────────────────────┴─────────────────────┐
       Procedure  ──────  "Make 1000 kg of Vaccine X"
            │
       Unit Procedure  ──  "Prepare medium in fermenter F1"
            │
       Operation  ────────  "Heat F1 to 37°C"
            │
       Phase  ────────────  "RampHeat" (single command sequence)
       
                            ◀──── decouples from ─────▶

                                  PHYSICAL MODEL
                                 (the "where to do it")
                                          │
       ┌──────────────────────────────────┴─────────────────────┐
       Enterprise        "Pfizer"
            │
       Site              "Puurs facility"
            │
       Area              "Vaccine manufacturing area 2"
            │
       Process Cell      "Cell-A : 4 fermenters + 2 mixers + filter"
            │
       Unit              "Fermenter F1"
            │
       Equipment Module  "F1's jacket cooling system"
            │
       Control Module    "Single valve XV-101"

The separation is the key insight: a recipe (procedural) doesn’t bind to specific equipment until the equipment phase is invoked. Same recipe, different unit, different control module — but the operator’s view is consistent.

The phase paradigm

A phase is the smallest reusable building block. Example phases in a typical chemical plant:

• Charge_Liquid (parameters : volume, source tank, target unit)
• Charge_Solid (parameters : mass, ingredient tag, target unit)
• Heat_To_Setpoint (parameters : target T, ramp rate, hold time)
• Cool_To_Setpoint
• Hold_At_Setpoint (parameters : duration, max T deviation)
• Mix (parameters : RPM, duration)
• Sample
• Discharge
• Clean (CIP / SIP)

A pharmaceutical batch operation procedure becomes a sequence of phase calls. The recipe author specifies the parameters, the equipment phases handle the actual interlocks and detailed sequences on the specific reactor / fermenter.

ISA-88 with ISA-95 — the manufacturing OS

ISA-88 describes how to execute a batch. ISA-95 describes the integration between business systems (ERP) and manufacturing execution (MES/DCS). Together they form the “manufacturing OS” model:

• ERP places a production order
• ISA-95 transfers it to MES
• MES creates a control recipe (ISA-88) from the master recipe
• Batch DCS executes phases on units
• Execution data flows back via ISA-95 to ERP/quality systems
• Batch records produced per ISA-88.04 + GMP requirements (21 CFR Part 11)

This integration is what makes large-scale pharma manufacturing auditable and traceable.

Modern evolution : ISA-106, ISA-18.2 alignment

ISA-88 is sometimes criticized for being too rigid for procedural automation of continuous processes (startup, shutdown sequences). ISA-106 extends ISA-88 thinking to continuous operations. ISA-18.2 (alarm management) defines how alarms interact with batch states (suppressed during transitions, etc.).

For practitioners, the integration with GMP / 21 CFR Part 11 is the daily challenge: every recipe change is a regulatory event (validation, change control). ISA-88’s recipe versioning model maps to GMP requirements but the workflow burden is significant.