Arc Flash DANGER vs WARNING Labels: Which Word and When

Last Updated: 2026-10-08

Answer Capsule: NFPA 70E-2024 does not set a voltage or cal/cm2 cutoff for DANGER versus WARNING on arc flash labels. WARNING is the common choice. Under ANSI Z535.4, DANGER is reserved for hazards that will result in death or serious injury if not avoided. Some owners use DANGER above 40 cal/cm2, but that is a program choice, not a code rule.

Your engineer's label data says 42 cal/cm2 on the main switchboard and 3.1 cal/cm2 on a lighting panel. Do both get WARNING? Does the big one get DANGER? Ask five electricians and you get five answers, and at least one will swear the code sets a cutoff. It does not. Print Pro AZ prints arc flash warning labels and DANGER labels every week, and the signal word question comes up on nearly every commercial order.

This post settles it. You get what NFPA 70E-2024 actually says about signal words and what ANSI Z535.4 says each word means. You also get the header color for each word. And you get a simple way to write the choice into your safety program so every label on the site matches. Brent Hanke, founder of Print Pro AZ, has seen every version of this argument, and the answer is shorter than most crews expect.

Does NFPA 70E Require DANGER or WARNING on an Arc Flash Label?

NFPA 70E-2024 requires neither word by name and sets no voltage or cal/cm2 line between them. Section 130.5(H) lists the data the label must carry: nominal system voltage, arc flash boundary, and at least one PPE value. It says nothing about the signal word.

The National Electrical Code is the same. Section 110.16 requires the equipment to be marked to warn qualified persons of the arc flash hazard. It points to 110.21(B) for the marking itself. That section requires effective words, colors, or symbols, and its informational note sends you to ANSI Z535.4. So the signal word comes from ANSI Z535.4 and from your own program, not from a code table.

What that means on the job: No inspector can fail a label for saying WARNING instead of DANGER based on NFPA 70E or the NEC alone. The same goes the other way around. They can fail it for missing data. Our NFPA 70E 2024 arc flash label requirements guide covers the data fields. This post covers the word at the top.

What Do DANGER and WARNING Mean Under ANSI Z535.4?

Under ANSI Z535.4, DANGER means a hazard that will result in death or serious injury if not avoided. WARNING means a hazard that could result in death or serious injury if not avoided. The difference is "will" versus "could." DANGER is reserved for the most extreme situations. Each word also has a fixed header color and uses the safety alert symbol, the triangle with an exclamation point.

Signal word	ANSI Z535.4 meaning	Header colors	Use on arc flash labels
DANGER	Will result in death or serious injury if not avoided	White letters on safety red, with the safety alert symbol	Program choice for the highest-energy gear, often above 40 cal/cm2
WARNING	Could result in death or serious injury if not avoided	Black letters on safety orange, with the safety alert symbol	The common default for arc flash labels
CAUTION	Could result in minor or moderate injury if not avoided	Black letters on safety yellow, with the safety alert symbol	Not appropriate for an arc flash hazard
NOTICE	Information not related to personal injury	White letters on safety blue, no safety alert symbol	Never for arc flash

Read the table from the bottom up. An arc flash can kill, so CAUTION and NOTICE are out. That leaves two words, and the choice between them is about how certain the injury is, not how likely the arc is.

When Should an Arc Flash Label Say DANGER?

An arc flash label should say DANGER when your electrical safety program says so, and the common trigger is incident energy above 40 cal/cm2. Here is why that number shows up so often. Table 130.7(C)(15)(c) in NFPA 70E tops out at CAT 4, which is a 40 cal/cm2 minimum arc rating. Above that, no PPE category covers the worker, and most programs prohibit energized work on the gear. "Will result in death or serious injury" fits.

Some owners set the DANGER line at a different value, and some never use DANGER at all. All of those are legal under NFPA 70E. What matters is that the rule is written down in the program required by NFPA 70E 110.3 and applied to every label on the site.

Field note: Many owners use DANGER above 40 cal/cm2. That is a program choice, not a code rule. If an inspector or auditor tells you it is required, ask for the section. There is not one.

Why Is WARNING the Right Default for Most Arc Flash Warning Labels?

WARNING is the right default because most arc flash hazards fit the ANSI Z535.4 definition. The injury could happen, but it is not certain. It also keeps the site readable. If every panel says DANGER, the word stops meaning anything. The crew cannot tell the 42 cal/cm2 main from the 3.1 cal/cm2 lighting panel at a glance.

Here is a call Print Pro AZ gets every month. A facility has three generations of labels from three vendors. Some 480 V gear says DANGER, some says WARNING, and the values on those labels overlap. Nothing in the code fails it. But the crew cannot tell which gear is worse, and the safety manager wants one rule for the whole plant. The fix is one signal word rule, one relabel, and one data table.

Your takeaway: Pick WARNING as the default. Add DANGER only if your program defines a trigger, and write that trigger down before the labels are printed.

What Colors and Symbols Go on an Arc Flash Warning Label?

The header color follows the signal word: safety orange for WARNING, safety red for DANGER, with the safety alert symbol beside the word. The message panel below it is black text on white. That is the ANSI Z535.4 layout, and it is what most engineers and AHJs expect to see.

Color matters more than it looks. NEC 110.21(B) requires the marking to be durable for the environment and not handwritten. In Arizona sun, a cheap vinyl label loses its orange and drifts toward yellow. At that point a WARNING header reads like CAUTION from ten feet away. Print Pro AZ prints arc flash labels on UV-rated polyester and .048 aluminum so the orange stays orange and the date stays readable. If your owner has a house format, the custom labels team matches it.

OSHA sits behind all of this. 29 CFR 1910.335(b)(1) requires safety signs, symbols, or tags to warn employees about electrical hazards. OSHA does not name a signal word for arc flash. It enforces the hazard through the General Duty Clause and points to NFPA 70E as the accepted method.

How Do You Write the Signal Word Rule Into Your Safety Program?

You write one sentence into the electrical safety program, send it to the engineer, and print every label from the same table. Here are the steps:

1. Pick the rule. Either "WARNING on all arc flash labels" or "WARNING by default, DANGER above 40 cal/cm2."
2. Add that sentence to the electrical safety program required by NFPA 70E 110.3.
3. Send the rule to the engineer so the study's label table includes a signal word column.
4. Send the table to Print Pro AZ as a PDF, Excel, or CSV file. The signal word comes from the column, not from a guess at the print shop.
5. Walk the site and replace any old label whose signal word breaks the rule.

Why the column matters: The most common signal word mistake Print Pro AZ sees is not the wrong word. It is a mix of words across the same site because three different people made three different calls. One column in one table ends that.

Frequently Asked Questions

Is a DANGER arc flash label required above 40 cal/cm2?

No. NFPA 70E-2024 sets no cal/cm2 cutoff for DANGER versus WARNING. Many owners choose DANGER above 40 cal/cm2 because that is the top of the PPE category table, but it is a program decision. Write it into your electrical safety program if you use it.

Can I use CAUTION on an arc flash label?

No. Under ANSI Z535.4, CAUTION is for hazards that could result in minor or moderate injury. An arc flash can result in death or serious injury, so the signal word must be WARNING or DANGER.

What color is an arc flash warning label?

A WARNING label has a safety orange header with black letters and the safety alert symbol. A DANGER label has a safety red header with white letters. The message panel on both is black text on a white background.

Does OSHA require a specific signal word on arc flash labels?

No. OSHA 29 CFR 1910.335(b)(1) requires signs or tags to warn employees about electrical hazards but does not name the word. OSHA enforces arc flash protection through the General Duty Clause and treats NFPA 70E as the accepted approach.

Conclusion

Three things to remember. First, NFPA 70E and the NEC set no line between DANGER and WARNING, so the signal word is a program choice guided by ANSI Z535.4. Second, WARNING is the right default, and DANGER belongs only where your program defines a trigger, most often above 40 cal/cm2. Third, the header color has to survive the environment, or the word on the label stops meaning what it says.

One written rule and one data table give you a site where every label matches. That is what an auditor wants to see, and it is what your crew needs to read the hazard at a glance.

Ready to print a matched set? Browse the arc flash label collection or call Brent: (602) 649-5305.

Sources

• NFPA 70E, Standard for Electrical Safety in the Workplace
• NFPA 70, National Electrical Code
• OSHA 29 CFR 1910.335, Safeguards for Personnel Protection

Brent Hanke | Print Pro AZ | (602) 649-5305 | b.hanke@printproaz.com

Brent Hanke is the founder of Print Pro AZ, supplying NEC-compliant labels to contractors across the country.