Field Guide
Warnings, Cautions, and Notes
The Vocabulary
Four Signal Words, One Missing
ANSI Z535.6, currently at its 2023 revision, is the standard for product safety information in manuals, instructions, and other collateral materials. It is the manual-facing member of the Z535 family, where the more familiar Z535.4 governs the safety labels stuck to the machine itself. It shares its signal words with that sibling, and there are four of them:
A hazardous situation that, if not avoided, will result in death or serious injury.
Reserved for the extreme case. Overusing it is the fastest way to make every other signal word invisible.
A hazardous situation that, if not avoided, could result in death or serious injury.
The workhorse for genuine personnel hazards.
A hazardous situation that, if not avoided, could result in minor or moderate injury.
Still about people. This is the one most often misused.
A message addressing property damage, not personal injury.
The category most teams are missing, and the reason their CAUTION statements are wrong.
The one most teams do not have is NOTICE, and its absence is why their CAUTION statements are wrong. Under Z535.6 all three of DANGER, WARNING, and CAUTION concern injury to a person, separated only by severity. The moment the risk is damage to equipment rather than harm to a human, the signal word is NOTICE. A library that has been writing “CAUTION: damage to the actuator may result” for a decade has a systematic conformance problem, and it is not a cosmetic one, because the reader has been taught that CAUTION sometimes means the machine and sometimes means them.
The Collision
The Same Words, a Different Rule Book
Now the part that catches people, because it catches them quietly. Defense technical manuals do not run on Z535.6. They take their style and format direction from MIL-STD-38784 and from the content standard cited for the manual type, whether that is MIL-STD-40051, MIL-STD-3001, or an S1000D program under service business rules. In that world the long-standing convention is different: WARNING for hazards to personnel, CAUTION for damage to equipment, and NOTE for emphasis that carries no hazard at all.
Read those two paragraphs together and the trap is obvious. CAUTION means people in one rule book and equipment in the other. A manufacturer that sells commercially and also delivers into a defense program is running both conventions, often through the same authoring team and sometimes through the same source content. The failure mode is not that someone breaks a rule. It is that someone applies the right rule from the wrong standard, which reads as perfectly correct to everyone who reviews it.
So the first question on any safety content is not how to word it. It is which standard governs this deliverable, which is the same question our TMCR and contract review pieces keep arriving at from other directions. Cite it in the business rules, and make it a property of the deliverable rather than a habit of the author.
Placement
Four Types, and Only One Is Inline
The half of Z535.6 that gets skipped is placement. The standard distinguishes four kinds of safety message by where they sit and what job each does:
General safety information
Front of the documentBroad safety instructions that apply across the product, gathered before the reader reaches any procedure.
Grouped safety messages
A dedicated sectionMultiple safety messages collected together, either as their own chapter or as a standalone safety document.
Section safety messages
Start of a chapter or sectionHazards specific to that part of the product or that phase of work, placed before the work begins.
Embedded safety messages
Inline, in the stepThe warning that sits directly in the instruction, so the reader meets it at the moment of the action rather than forty pages earlier.
The embedded message is where structured content quietly earns its keep. A warning has exactly one job, which is to be read before the action it concerns, and a warning that arrives after the step has failed completely regardless of how well it is written. In a page layout that binding is a matter of luck: a reflow moves it to the next page, a template change orphans it, a reused procedure leaves it behind. In a content model the warning is a child of the step, so it travels with the step wherever the step goes, and a business rule can refuse to build content that puts it anywhere else.
This is also why DITA 2.0 is redesigning its hazard statements to align with Z535.6, with support for multiple hazard symbols. A specification is catching up with a standard its users were already obliged to follow. If you hold DITA content with hand-rolled warning markup, that alignment is one more line on the migration list.
Writing Them
Say the Hazard, the Consequence, the Avoidance
The wording convention is simple enough to hold in your head and unevenly applied almost everywhere: name the hazard, name the consequence of not avoiding it, and say how to avoid it. “High voltage” on its own is a label, not a safety message. “ High voltage inside the enclosure. Contact will cause severe burns or death. Disconnect and lock out supply before opening.” is a safety message, and the difference is that a reader can act on the second one.
Two habits keep safety content honest at scale. Write the messages in controlled language if your program uses it, because a safety message is the worst possible place for a sentence the reader has to parse twice. And manage the hazards as shared, reusable content rather than retyping them, so that when a hazard assessment changes, every procedure that references it changes with it. The alternative is a library where the same hazard is worded eleven ways and nobody can prove which version a technician actually read.
FAQ
Questions We Hear
What is ANSI Z535.6?
The American National Standard for product safety information in product manuals, instructions, and other collateral materials, currently at its 2023 revision. It is the manual-facing member of the Z535 family, where the better-known Z535.4 covers safety signs and labels on the product itself. Z535.6 defines the signal words a manual uses, the four kinds of safety message and where each belongs, and how safety content should be formatted and located so a reader actually encounters it.
What is the difference between a warning and a caution?
Under ANSI Z535.6 both concern personal injury and the difference is severity: WARNING covers a hazardous situation that could result in death or serious injury, CAUTION covers one that could result in minor or moderate injury. The point people miss is that CAUTION is still about people. If the risk is damage to equipment rather than harm to a person, the correct signal word is NOTICE. DoD technical manuals use a different convention, where CAUTION conventionally covers equipment damage, which is exactly why a team writing to both needs to know which rule book governs the deliverable.
Does ANSI Z535.6 apply to military technical manuals?
Not by default. DoD manuals get their style and format direction from MIL-STD-38784 and the content standard cited for the manual type, and those carry their own conventions for warnings, cautions, and notes. Z535.6 governs commercial and industrial product documentation, and it reaches military work indirectly, through commercial items delivered into defense programs and through manufacturers who maintain one authoring standard across both markets. The mistake to avoid is assuming the conventions are interchangeable because the words look the same.
Where should a warning go in a procedure?
Before the step it concerns, always, and that is not a formatting preference. A warning placed after the action it was meant to prevent has failed at the only job it had. Z535.6's embedded safety message type exists for precisely this, and it is the reason structured authoring handles safety content better than page layout does: in a content model the warning is bound to the step, so it cannot drift onto the next page during a reflow, get orphaned by a layout change, or be dropped when someone reuses the procedure somewhere else.
Why is DITA 2.0 changing its hazard statements?
To align with ANSI Z535.6, including support for multiple hazard symbols in a single statement. It is a good example of a specification catching up with a standard its users were already obliged to follow, and it means a DITA library carrying hand-rolled warning markup has a migration ahead of it. For anyone holding DITA content, this is one more item on the same list as the rest of the 2.0 removals.
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Safety Content That Holds Up
We model warnings and cautions as structured content bound to the steps they protect, conformant to the standard your contract actually cites rather than the one your authors are used to.