# ISA-88 — Batch Control

> ISA-88 (also known as IEC 61512) defines the standard model and terminology for batch control systems. It provides a unified language for recipes, equipment, and procedural control that lets pharmaceutical, food, and chemical batch plants describe their processes consistently.

- Source : https://industryhub.site/en/standards/isa-88
- Body : ISA
- Family : Process Control
- Status : current
- First published : 1995
- Latest revision : 2010 (current Edition for Part 1)
- Edition : varies per part
- Next revision : Stable, ongoing maintenance
- Access : Paid (ISA store / IEC ~150-300 CHF per part)
- Language : English

## Document structure

- **ISA-88.01 / IEC 61512-1** — Batch control — Part 1: Models and terminology : Foundation. Defines physical model (Site → Area → Process Cell → Unit → Equipment Module → Control Module) and procedural model (Procedure → Unit Procedure → Operation → Phase).
- **ISA-88.02 / IEC 61512-2** — Data structures and language guidelines : How to exchange recipe data between systems. XML schemas, B2MML basis.
- **ISA-88.03 / IEC 61512-3** — General and site recipe models and representation : Master recipe and control recipe data structures.
- **ISA-88.04 / IEC 61512-4** — Batch production records : What must be recorded during execution, how to format batch reports for GxP / GMP regulators.

## Key concepts

- **Physical Model** : Hierarchical equipment model : Enterprise > Site > Area > Process Cell > Unit > Equipment Module > Control Module. Each level is an abstraction layer for control and reporting.
- **Procedural Model** : Hierarchical recipe model : Procedure > Unit Procedure > Operation > Phase. A 'Procedure' describes the full batch ('Make 1000 kg of compound X'). 'Phases' are the smallest reusable building blocks ('Add water', 'Heat to 60°C', 'Discharge').
- **Recipe** : Combines product formula + procedure + equipment requirements + master scheduling. Types : Master Recipe (template), Control Recipe (instance for one batch), Site Recipe (network of master recipes across multiple sites).
- **Equipment Phase** : A piece of control logic implementing one phase on specific equipment. Reusable. Example : phase 'AddWater' on the 'Mixer1' equipment module. Equipment phases hide the equipment-specific implementation from the recipe.
- **Unit** : A piece of equipment that processes one batch at a time and can hold material throughout the batch (a reactor, a fermenter, a mixer). 'Unit allocation' is the scheduling problem : which batch goes on which unit when.
- **B2MML** : Business to Manufacturing Markup Language. XML schema for exchanging ISA-88 (and ISA-95) data between ERP, MES, batch system. WBF / OAGi maintained.

## 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.

## Applicable industries

Pharmaceutical manufacturing (most batch-heavy), Food and beverage processing, Specialty chemicals, Personal care and cosmetics, Paints and coatings, Biotech upstream / downstream processes

## References & further reading

- [ISA-88 / IEC 61512 — ISA portal](https://www.isa.org/standards-and-publications/isa-standards/isa-88-batch-control)
- [WBF — World Batch Forum (technical papers)](https://www.wbf.org/)
- [OAGi / B2MML schemas](https://oagi.org/B2MML)