It happened once again! In one of my training programs, someone asked the all-too-familiar question, “What color should arc flash warning labels be?” It’s no wonder people are confused. This question could have more than one answer.

Danger, warning, caution
Part of the confusion is that neither NFPA 70E nor the National Electrical Code (NEC) provide any specific guidance about what color or word to use for an arc flash label. Informational Note No. 2 found in NEC Article 110.6 references ANSI Z535.4 1998 Product Safety Signs and Labels, and NFPA 70E 130.7(E)(1) and Table 130.7(F) reference the entire ANSI Z535 series. This ANSI standard is where you find the definitions of the words “danger,” “warning” and “caution,” which also are referred to as “signal words.” According to the ANSI standard, each word with its appropriate color is defined as follows:

• Caution (yellow): Indicates a hazardous situation that, if not avoided, could result in minor or moderate injury
• Warning (orange): Indicates a hazardous situation that, if not avoided, could result in death or serious injury
• Danger (red): Indicates a hazardous situation that, if not avoided, will result in death or serious injury

According to the ANSI Z535 definition, the word “danger” with the color red seems like the most logical choice for all arc flash labels. With the exception of a very minor arc flash, most arc flash events pose a likely risk of serious injury or death unless proper protection is used or the hazard is avoided. But the problem is, if every label had a bright red background with the word “danger” on it, the message’s importance could diminish.

The two-color approach
Many in the industry use both red and orange labels. Red with the word “danger” is reserved for more extreme risks, and orange with “warning” is used everywhere else. With this method, deciding when to use red/danger or orange/warning depends on the calculated incident energy.

NFPA 70E Informational Note No. 3 specifically references 40 calories per centimeter squared (cal/cm2) as an upper limit where more emphasis may be necessary with respect to de-energizing the equipment. This value is often used to decide which level of warning to use. Equipment with a calculated incident energy of 40 cal/cm2 or greater receives a red/danger label, and everything else would use an orange/warning label.

Survey—what does everyone do?
Although the two-color labeling method is common, its use can generate a lively debate among people in the arc flash community. You can ask several people what colors and words they use, and you are likely to receive several different answers since interpretations vary. To help identify the more common approaches for label color and signal word selection, I decided to ask this question at “ANSI Z535 defines the words ‘danger,’ ‘warning’ and ‘caution’ as well as the respective colors red, orange and yellow, which is widely used in the United States. NFPA 70E defines the minimum information to be an arc flash label but leaves the color code and signal words up to the user. Which of the following do you use for your labeling?” The choices were as follows:

• Red/danger for 40 cal/cm2 and above with orange/warning for locations below 40 cal/cm2
• Red/danger for all labels
• Orange/warning for all labels
• Something else, such as yellow/caution

Although far from a scientific survey, the results provide insight into what colors and signal words are being used. Of all respondents, 70 percent indicated they use the two-color approach with the color orange and signal word “warning” everywhere, except for locations where the calculated incident energy is 40 cal/cm2 or greater. At these locations, the signal word “danger” with the color red is used. Of the remaining respondents, 23 percent use orange and “warning” for every label, 6 percent used red and “danger” for every label, and 1 percent did something else.

Although NFPA 70E may provide direction about where labels are required and the minimum information that is necessary, the signal words and color selection is not black and white and sometimes becomes a gray area. And gray is not one of the color choices found in ANSI Z535.

PHILLIPS, founder of and, is an internationally known educator on electrical power systems and author of “Complete Guide to Arc Flash Hazard Calculation Studies.” His experience includes industrial, commercial and utility systems, and he is a member of the IEEE 1584 Arc Flash Working Group. Reach him at