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Danger, Will Robinson! Trefoil history and alternate history

Danger and hazard symbols are a funny thing. They’re a deadly serious topic (or else they would not be necessary), but they seem to spark quite a bit of fanciful creativity. They inherently need to communicate dangerousness without the use of words (or else we would just write the words instead…), but in many cases they take context if not full-blown interpretation to understand.

Adapted from // Public domain

Hot hot hot!

The classic example is the “trefoil” radiation symbol, which has inspired scores of imitators. It is iconic to the point where it gets copied, but somehow most of the copies fail to convey their message of impending peril as effectively as the original.


Berkeley beamers

The trefoil as we know it today was invented, so we’re told, in 1946 by a group of brainstormers holed up at the University of California Berkeley’s Radiation Laboratory. The design brief was to communicate the presence of hazardous ionizing radiation. That’s radiation that packs enough energy to knock the electrons off of atoms that it hits, which in turn fouls up the chemical bonds that those atoms can form and, when those atoms are you, seriously ruins your day. Non-ionizing radiation is the harmless stuff like radio waves and flashlight beams that bounces off of solid objects, gets lost in the drapes, and generally does no one any harm (apart from your step-uncle in Idaho who picks up demonic transmissions whenever he knowingly drives past a cell tower and tells you on Facebook about the alleged “road crew” that was out pulling reels of heavy-duty cable on the edge of town where he knows there isn’t any electric service to need cable, so what were they really doing out there?).

Anyway, the Berkeley Radiation Lab doodled up several possibilities, but they settled on the trefoil design and, eventually, went with a magenta-on-yellow color combination. Red and white was too similar to the fire department, blue did not signify “danger” and it faded too easily, and so on. In 1948, Brookhaven National Laboratory also decided it was in need of an ionizing-radiation symbol, so J.H.B. Kuper wrote to Berkeley asking for details on that symbol. Meetings were held, samples were scrutinized, and what came out of it all was the symbol we hold near & dear to our hearts today.

Radiation prototype on green

Reject from a green-field deployment at Berkeley.

An interesting factoid about the trefoil symbol (as Nels Garden related it to Lloyd Stephens and Rosemary Barrett for their 1978 article A Brief History of a “20th Century Danger Sign”) is that the Berkeley brainstormers chose the design we’re familiar with because it suggested rays or radiation shooting out of the nucleus of an atom. Other possibilities were recorded by Stephens and Barrett, including a skull-and-crossbones, a mushroom cloud, something a little harder to discern from the sketches, and a combination skull-and-crossbones-and-trefoil.

Radiation trefoil discussion

For the last time, Hanford, draw with your whole arm not just the wrist.

A second interesting factlet is that the group seems to have rejected several alternate versions of the trefoil design that sound more complicated, especially “signs that incorporated straight or wavy arrows between, or inside, the propeller blades.” Examples are hard to come by, but here are two:

Radiation trefoil prototype

Radiation goes out; fear goes in.

Radiation trefoil prototypes

Wave–particle duality: solved.

Simplicity wins when the opponent is headed toward your internal organs at the speed of light, evidently.


One has to be civil

So we’ve had the radiation trefoil for 70 solid years now. About a dozen years after the trefoil’s adoption, we got its first spin-off. Much to our collective surprise, it turned out that friendly folks here in the US of A weren’t the only ones with ionizing radiation sitting around, and once someone lobs theirs in your direction, you’d better have some place suitable to duck and cover. So, in 1961, the Office of Civil Defense rolled out the “fallout shelter” symbol. It copied the three-armed skeleton of the radiation trefoil, but without the central “source” circle and with an enclosing exterior circle.

You don't have to mutate at home but you can't stay here.

You don’t have to mutate at home but you can’t stay here.

Bill Geerhart reports that the design of the symbol was commissioned to Blair, Inc of Fairfax, VA—and that the trefoil-derived design was added to a shortlist of options sent up for CD management to choose from primarily because it looked familiar, not because it was the favorite.

Credit for the design goes to Robert W. Blakeley of Blair, Inc. Unfortunately, it seems that the other proposed designs have been lost to Father Time, but Geerhart favors us with one description of an alternate design for the full fallout-shelter sign: “one of them…showed a family of three, holding hands, moving graphically across the center…” In a subsequent e-mail he expanded upon this description slightly: “[it] showed a family of three moving in depth perspective to a shelter, had a small trefoil, without the center dot, in shadow background.”  Think that sounds rough? Hey, you try describing a graphic design project on the phone sometime.


Extreme biology

Given a favorable mood and the right background music, one could easily forgive the Office of Civil Defense for its act of sparking the now rampant trefoil-derivatives market. After all, ionizing radiation and fallout shelters are but two sides of the same coin, particularly when it’s a 1961 coin.

Where things took an irrevocable turn toward toothpaste-out-of-the-tube territory, though, is with the biohazard symbol. In 2001, The New York Times reported that the symbol was invented by the fun-loving folks at Dow Chemical in 1966. The process involved a series of focus groups led by Dow’s Charles Baldwin, in which participants were shown a variety of symbol proposals over a few days. The creepy-looking symbol that won was the one that scored highest on the metrics of ‘being memorable’ and ‘not reminding you of something else.’

Biological hazard trefoil symbol

Look out: it’s got biology!

What’s notable, though, is that unlike the radiation trefoil, the biohazard trefoil has no symbolic meaning; the shape at the center and the arms jutting out do not represent anything, although they are somewhat suggestive of “something alive.” They’ve been variously described as insectoid mandibles, antennae, some sort of bacterial flagella, or simply something that’s spreading.

All of those images are encompassed in the “biohazard” category, which is itself another change. Unlike ionizing radiation, there is not a single, well-agreed-upon definition for “biological hazard.” Certainly it includes infectious agents like viruses, but it also includes medical waste and various toxic compounds that could cause sickness or disease. In truth, there is a lot of overlap between things that are deemed biological hazards and things that are deemed “poisons”—though, when you dig into it, there isn’t a universally accepted definition for what qualifies as a poison, either.

Sadly, records of what the other candidate symbols tested against Dow’s biohazard trefoil were are also hard to come by. But Harvard Medical School did reprint a copy of the Times story, which itself is now only accessible through the Internet Archive’s Wayback Machine, and that copy of the story included one picture showing three alternate designs:

Rejected biohazard symbols

In this tub are all my hopes and dreams and also some Ebola.

One factor that seems fairly clear by this point is that the trefoil arrangement had already become identified with the notion of “danger,” which helps explain why it was the model for this first non-radiation-related hazard symbol. Beyond that, it’s hard to say where the alternate candidates miss the mark. The one on the left is clearly an iteration on the same design eventually selected, but the other two, absent of years of context, appear strangely non-threatening.

Rejected biohazard symbol 1

Do not open: high risk of jesterification.

Rejected biohazard symbol 2

Yeah but if you stare long enough then anything looks like a beaker.

Rejected biohazard symbol 3

Doing the things a triangle can.

Deciding what these other candidate symbols suggest can be a fun party game, if you go to parties with infectious-disease researchers or whomever the Tom Hanks character from The DaVinci Code was based on.

One final note about the abstractness of the biohazard trefoil is that it bears a perplexing similarity to the Bordeaux area of France’s regional coat-of-arms. Although, depending on how you feel about wine, perhaps there’s no coincidence to explain away at all. Either way, it seems to be no conspiracy (at least for now).

Bordeaux symbol

Captain, these culture readings are off the charts.


Man vs chemical

So, for the benefit of those of you nodding off, with the fallout-shelter symbol we lost a little of the radiation trefoil’s direct connection to the source of the threat (beams of energy), and with the biohazard symbol we moved a bit further away still: the symbol has no graphical connection to the danger at all; it only looks scary and can ride the coattails of the original symbol’s established connection to “something bad.”

The next iteration (and, as far as I can tell, the most current) of the hazard trefoil is the “chemical weapons” symbol. Here again, the design is constructed on a trefoil frame, but using geometric shapes. This is the symbol you might find plastered on the sides of containers of nerve gas or Sarin, or perhaps really strong acid (not that kind, hippie). Or, at least, Wikipedia calls it the “chemical weapons” symbol and gives it an appropriate color as proof:

How will they know it's military if it's not green?

Well, we do know that the army buys a lot of green paint.

Turns out it was meant to be more general than that, although it was created by the military. The US Army Office of the Surgeon General runs (or ran) a training program call the Nuclear, Biological, and Chemical Casualty Training System (NBC CTS). Though offline today, the Wayback Machine has a copy of a page from the site explaining that the symbol was created to match the design of the existing radiation and biohazard trefoils.

“When NBC CTS was first created, it bothered us not only that the chemical symbols differed so greatly in design from the nuclear hazard and biological hazard symbols, but also that there was more than one standard in use. It was for this reason that we constructed our own chemical hazard symbol, as seen above. It has an atom-like look to it, which is appropriate for chemicals.”

Indeed, the most obvious connection the chemical hazard symbol has is to ball-and-stick models of atoms, which are often used to visualize chemical compounds. But it’s interesting that this connection sounds like a happy coincidence. So, too, we should note that the page does not describe the symbol as being reserved for chemical weapons, but for hazardous chemicals in general. The only other design note available is a tibit on the downloads page that calls out the biohazard symbol for being “just plain cool.” Hey, you get no argument here, doc.

Ask your doctor if chemicals are right for you.

Ask your doctor if chemicals are right for you.

It’s hard to say exactly when the design was created (at least it is for me, unwilling as I am to do more than search around online for part of a day), but the NBC CTS has been around since at least 2000, although there are not a lot of records predating that time period. So the symbol could be rather new. It also has not caught on to the same degree as its elder siblings—perhaps due to time, perhaps since there is already a wide variety of other symbols that the lab-coat crowd uses to mark dangerous chemical substances. And if we may speculate a touch, “chemical” is perhaps just a bit too broad for a single clear sign to cover all the possibilities. After all, cyanide, hydrochloric acid, and nitroglycerin are all dangerous chemicals, but what each does (and how you need to protect yourself from them) varies considerably.

The archived page does not show or describe any alternate design concepts, but it does mention what was in use before. “A few years ago, there had been three variations of the chemical hazard symbol in use. One was a picture of a death’s head, or skull and crossbones. The other was a beaker. The last was a pair of beakers with their necks crossed.” That latter two don’t sound like we’re missing out on much, but the first does indicate the acceptance problem: the skull-and-crossbones already represents “poison” to most people who have a skeleton or know what one is.

The radiation trefoil, on the other hand, was invented because researchers needed a new symbol to represent a new type of danger. It’s hard to say if the biohazard symbol meets that same criteria or not; there were certainly viruses prior to 1966, but perhaps our perception of them changed as they became something to study or, even, create in laboratory conditions. One thing is for sure, though: the radiation trefoil was so successful that its three-fold design was assumed to be the right starting place when NBC CTS started its own design process.


Caution: speculative fiction sighted

Most interesting of all, however, is the fact that this same assumption continues to this day. The trefoil’s iconic shape inspires people to develop their own danger signs, representing more recent hazards and even threats that are entirely hypothetical. In particular, the science-fiction industry (Big SciFi, as your step uncle calls them) has developed a penchant for spawning trefoil-like hazard symbols regularly, for every looming threat from antimatter to zombies. But that’s a subject for part two, next week.

In the meantime, if you do happen to know of additional historical or rejected trefoil hazard designs—or if you have any more information about the design process for the symbols shown—please do get in touch.  Until then, here’s a gallery of all of the symbol designs seen so far, partly to serve as a convenient article thumbnail, but mostly just to leave you with something to think about.

Trefoils past and present

So much danger; so many choices.


  1. nim
    June 3rd, 2016 | 2:49 am

    Another influence was clearly the triangular “danger” road signs (triangle with bottom base). The original design was quickly inverted to match this basic shape.


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