The 2015 Edition of NFPA 70E 130.7(A) Informational Note 3 stated:

Informational Note No. 3: When incident energy exceeds 40 cal/cm2 at the working distance, greater emphasis may be necessary with respect to de-energizing when exposed to electrical hazards.

This note was deleted with the 2018 edition. Most people were using the signal word DANGER with a RED background for incident energy above 40 cal/cm2 based on this informational note. (Red/Danger is based on ANSI Z535 – this might be different in other countries)

This question is to check the pulse of the industry 5 years after this note was deleted.

For arc flash studies today, do you still use RED/DANGER on labels above 40 cal/cm2?
Yes
No
It depends
Your comments are always welcome!

There is no direct correlation between incident energy and arc blast pressure. This was identified by Dr. Ralph Lee in his original research from the late 1980s, but unfortunately a public comment was added to NFPA 70E that implied there was and at the 40 cal/cm2 incident energy level. Which happens to correlate with the old HRC 4 or now Arc Flash PPE Category 4.

Dr. Ralph Lee's research was published in the IEEE Yellow Book which is now IEEE 3007 series. You can view the graph that is included.

Danger signal pane should be at 140.1 cal/cm2 based on an employer's compliant Electrical Safety Program including a documented work task based risk assessment procedure.

Unfortunately over the last decade consulting engineers completing arc flash hazard incident energy analysis studies included an error in their reports and was propagated by the power system software vendors that wrongly automatically included a column in the "Results Table" for incident energy analysis that ≥40.0 cal/cm2 as "Dangerous" and "No PPE Exist." Both of these statements were and are false!!!!

Then the software automatically generated Danger single pane equipment labels. Software should not be used to make risk based decisions. Risk assessment is completed by the employer.

Employer's that commissioned studies were misinformed with respect to what I call the "40 cal myth!!!"

There is a lot of misinformation and disinformation related to abnormal arcing fault sustainability and arc flash published in social media, in reports issued and by "arc flash trainers." This is unfortunate.

That said employers can control the narrative related to electrical hazard identification/classification, detailed defendable risk assessment procedure and ensuring residual risk is as low as reasonably practicable by development, implementing and auditing a compliant Electrical Safety Program.

More than willing to discuss/debate this with any "arc flash trainer," consulting engineer etc. My email is terry.becker@twbesc.ca. or call me 587 433-3777.

Electric shock leading to electrocutions (which incident statistics prove) needs attention. Also be aware of electric shock sequelae!

What Jim said is correct. But most of the time, we use 40 calories as a break point between Warning and Danger labels. Here is how we go at this. We explain to the client that this is subjective decision and that the 40 calorie limit was a legacy requirement. That this 40 calorie limit is no longer enforced. That it was likely something that was decided based on the available PPE at that time. Generally, after clients hear this, they will still go with 40 calorie break point between warning and danger. What I usually hear is that above 40 calories, they will bring in a contractor to do the work. Sometimes it's another level, but it's their choice.

If the signs/labels are following the ANSI Z535 standard (not required by NFPA 70E), they would be using the following definitions.
From ANSI Z535.2-2011:
4.11.1 DANGER: Indicates a hazardous situation that, if not avoided, will result in death or serious injury. This signal word is to be limited to the most extreme situations.
4.11.2 WARNING: Indicates a hazardous situation that, if not avoided, could result in death or serious injury.
4.11.3 CAUTION: Indicates a hazardous situation that, if not avoided, could result in minor or moderate injury.

A long time ago the idea that 40 cal/cm^2 was a magical delineating line between Warning and Danger got started. Although that idea is debunked and many of the basis concepts outdated, Danger vs Warning label headers is not settled. It is still quite common for clients to specify that they want Danger at 40 and greater and Warning for less than 40.

Some of it is based on risk tolerance. For some they want to remain consistent with past practices. Some of it is based on very few people actually reading the ANSI Z535 standards and knowing what the differences are between the Danger and Warning definitions. Some of it is based on a desire to make certain IE level signs stand out. And some not knowing that there is no magical line at 40 cal.

Danger - will result in death or serious injury. What incident energy level will result in death? That isn't fixed. What is meant by "serious" injury?

Warning - could result in death or serious injury. What incident energy level could result in death? Again, there isn't a fixed level. Also, we have "serious" in there again. Is the warning level of "serious" different than the danger level of "serious"?

Hazard notifications signs/labels for arc flash are often also used for voltage hazard notification. In that case the risk of death/serious injury from the voltage hazard would also need to be considered.

So really, as long as the labels/signs are consistent throughout the facility/company and consistent with their electrical safety policies and procedures, does it really matter as long as they are at least using a Warning signal word?