Do we have to follow ISA standards?

Only where a specification, a contract, or a regulation cites them. No law requires ISA-101 for a water plant HMI. Following them is how a utility gets a system that any integrator can work on and that matches the practice of the profession, which is why specifications cite them.

What is the difference between ISA-99 and IEC 62443?

The same work. ISA-99 is the ISA committee that developed the security series and the original numbering; the standards are published jointly as ISA/IEC 62443 and referenced by the IEC number. The committee continues as ISA99.

Which ISA-5.1 edition should we use?

The current one, cited by year in the specification and the site tag standard. The 2009 revision made significant changes to the letter table and the symbols from the 1984 version that much of the installed base was drawn under; a site with older drawings decides whether to redraw or to carry both conventions with a note.

Are there ISA standards for water specifically?

No. ISA standards are process-industry generic, and water and wastewater apply them like any other process. The water sector has its own bodies, AWWA and WEF, whose manuals of practice reference ISA where control systems are involved.

ISA Standards for Controls | CurryControls.com

The short answer

ISA publishes the standards that define how control systems are drawn, tagged, alarmed, displayed, and secured. The ones a utility or an integrator uses most are ISA-5.1 for instrumentation symbols and tag numbering on P&IDs, ISA-18.2 for alarm management, ISA-101 for HMI design, ISA-20 for instrument specification forms, and the ISA-99 work that became the IEC 62443 security series. They are consensus documents, purchased from ISA, and they are cited in specifications so that everyone on a project draws, names, and designs the same way.

Key points

ISA-5.1 is why a level transmitter is LIT-101 on every drawing. Cite it in every specification.
ISA-18.2 defines the alarm management lifecycle; ISA-101 defines HMI design. Both are widely adopted in water.
ISA-20 gives the specification sheet forms for instruments and control valves.
ISA-99 is the origin of IEC 62443; the security series is now referenced by its IEC number.
Standards are purchased and cited by edition. A specification that cites one without an edition cites nothing.

What ISA is

The International Society of Automation is the professional society for automation and control practitioners, and its standards committees produce the consensus documents the profession works from. ISA standards are American National Standards through ANSI, and several have become international standards through IEC. They are written by committees of users, integrators, and vendors, revised on a cycle, and sold by ISA; a project that uses them purchases them, and a specification that cites them names the edition.

The standards a utility project uses

Standard	Title	What it is used for	Where on this site
ISA-5.1	Instrumentation Symbols and Identification	The tag letter codes and the graphic symbols on P&IDs and loop drawings; the reason FIT means flow indicating transmitter everywhere	P&ID drawings; instrument lists
ISA-5.4	Instrument Loop Diagrams	The content and format of loop drawings	Instrument lists; loop checks
ISA-18.2	Management of Alarm Systems for the Process Industries	The alarm lifecycle: philosophy, rationalization, design, monitoring; the definitions of an alarm, priority, floods, and states	ISA-18.2; alarm philosophy; rationalization; alarm floods
ISA-101	Human Machine Interfaces for Process Automation Systems	HMI design: display hierarchy, style guide, color use, alarm indication, navigation	ISA-101; high-performance HMI; faceplates; navigation
ISA-20	Specification Forms for Process Measurement and Control Instruments	The data sheet forms used to specify transmitters, switches, analyzers, and control valves	Instrument lists
ISA-88	Batch Control	The models and terminology for batch and recipe control; also the source of the equipment module and phase concepts used in sequence programming	State machines; sequences of operation
ISA-95	Enterprise-Control System Integration	The levels model and the interface between control systems and business systems; the origin of the level numbering the Purdue model uses	Purdue model; historian architecture
ISA-99 / IEC 62443	Industrial Automation and Control Systems Security	The security series, now published as IEC 62443 and referenced by that number	IEC 62443
ISA-84 / IEC 61511	Functional Safety: Safety Instrumented Systems	Safety instrumented systems for the process sector; relevant to chlorine gas systems and a few other utility applications	Interlocks
ISA-71	Environmental Conditions for Process Measurement and Control Systems	Classification of environments, including corrosive atmospheres such as hydrogen sulfide, for specifying equipment	Enclosure selection
The ISA-12 series	Hazardous location practices, including intrinsic safety	Instrument installation in classified areas	Headworks

How they are used on a project

In specifications: The engineer cites the standards the work must follow: ISA-5.1 for tags and symbols, ISA-18.2 for the alarm system, ISA-101 for the HMI, ISA-20 for the data sheets. The citation makes the standard a contract requirement, and the edition is named so that everyone reads the same document.
In site standards: A utility writes its tag convention, its HMI style guide, and its alarm philosophy as documents that apply the ISA standards to its own system. The standards give the framework; the site documents give the decisions.
In training: ISA courses and certifications, including the Certified Automation Professional and the Certified Control Systems Technician, are built on the standards and are the common credentials in the field.
In assessment: An alarm system is benchmarked against the ISA-18.2 metrics; an HMI is reviewed against ISA-101; a security program is assessed against 62443. The standards are the yardsticks.

Getting them

ISA standards are purchased from ISA directly or through standards resellers, individually or by subscription, and ISA members receive a discount. The free material is substantial: ISA publishes summaries, articles, and quick-start guides, the technical report abstracts describe what each report covers, and the InTech magazine and ISA blogs discuss application. A utility that will implement ISA-18.2 and ISA-101 seriously buys both standards and their technical reports; one that wants the vocabulary can start with the free summaries and the pages on this site.

Frequently asked questions

Do we have to follow ISA standards?: Only where a specification, a contract, or a regulation cites them. No law requires ISA-101 for a water plant HMI. Following them is how a utility gets a system that any integrator can work on and that matches the practice of the profession, which is why specifications cite them.
What is the difference between ISA-99 and IEC 62443?: The same work. ISA-99 is the ISA committee that developed the security series and the original numbering; the standards are published jointly as ISA/IEC 62443 and referenced by the IEC number. The committee continues as ISA99.
Which ISA-5.1 edition should we use?: The current one, cited by year in the specification and the site tag standard. The 2009 revision made significant changes to the letter table and the symbols from the 1984 version that much of the installed base was drawn under; a site with older drawings decides whether to redraw or to carry both conventions with a note.
Are there ISA standards for water specifically?: No. ISA standards are process-industry generic, and water and wastewater apply them like any other process. The water sector has its own bodies, AWWA and WEF, whose manuals of practice reference ISA where control systems are involved.

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