2638: Extended NFPA Hazard Diamond

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
Extended NFPA Hazard Diamond
With most labs, the hushed horror stories are about something like dimethylmercury or prions, but occasionally you'll get a weird lab where it's about the soda machine or the drop ceiling.
Title text: With most labs, the hushed horror stories are about something like dimethylmercury or prions, but occasionally you'll get a weird lab where it's about the soda machine or the drop ceiling.


This comic depicts an extension of the National Fire Protection Association's NFPA 704 Standard System for the Identification of the Hazards of Materials for Emergency Response "fire diamond" emblematic insignia used to warn about the properties of hazardous substances inside a building, vehicle, room, cabinet, or container that are important during an emergency or accident, such as a fire, earthquake, spill or leak, bringing the diamond from 2x2 squares to 3x3 by adding five variously useful and humorous squares along the bottom edges. NFPA Hazard Diamonds have also been mentioned in 868: Nolan Chart.

The numbers in a normal NFPA 704 diamond do not specify values of substances' properties, but rather broad categories designating characteristics of the substances of greatest interest to first responders and hazardous materials cleanup crews. Randall's expanded diamond breaks with this convention, with several squares (Lilac, Orange, and Black) denoting absolute values, and one square (Green) denoting an economic value. This could very easily lead to documentation update headaches, especially since the Green square is mostly determined by supply and demand, and the Lilac square is linked to political outcomes. See explanation for each field in the extended square below in the table.

The only easily identifiable substance which could likely meet the specific insignia numbers shown in the comic is thionyl chloride (SOCl2), a chlorinating reagent and solvent regulated as a chemical weapons precursor and sometimes used in the production of methamphetamine, which would also be represented with the W symbol inside the white square, indicating reactivity with water.

The title text (which references "scary stories" of the Black square) refers to dimethylmercury and prions. Dimethylmercury, C2H6Hg, is an organic form of mercury with an NFPA score of 4-4-3 (contact can be fatal, will burn below 73° F (22 °C), will combust if put under pressure). In 1997, an American chemist, Karen Wetterhahn, died 298 days after a few drops of C2H6Hg on her latex gloves were absorbed into her hand through the gloves, causing fatal mercury poisoning. Despite her having followed all safety protocols of the time, it was not then understood that the chemical was so toxic, nor that latex was so permeable to it. Prions are misfolded proteins that are responsible for a number of neurodegenerative diseases, including mad cow disease and chronic wasting disease in non-human animals and Creutzfeldt-Jakob disease in humans. These would indeed be the kind of substances that would scare those working with them in their labs; if an accident occurred, the results could be calamitous. See for example the case of Émilie Jaumain, a lab technician who died after accidentally coming into contact with prions in mouse tissue.

But a few labs have apparently had accidents involving a soda machine or dropped ceiling. The latter may be a reference to the death of Janet Parker: One inquiry found that she was infected with smallpox when a sample traveled upward from a lab on the floor below hers; however, other investigations have challenged that finding. There are occasional instances of vending machines causing injury or death, usually caused by people trying to shake or tilt the machines to get product out and having the machine tip and fall on them. On average, a couple of Americans per year are killed in this way. Reagents obtained in this way tend to have more impurities than those usually used in labs, but are relatively safe to shake.

Table of extended diamond[edit]

Squares and explanations
Square Color Comic text Explanation
Real NFPA 704 diamond square and number meanings
Top Red Flammability (0) Denotes flammability. 0 indicates "materials that will not burn."
Top Left Blue Health Hazard (4) Denotes the danger that the substance(s) pose to living beings in ways other than flammability and reactivity. 4 indicates that "Very short exposure could cause death or serious residual injury even though prompt medical attention was given."
Top Right Yellow Instability (2) Denotes how stable the substance(s) are when exposed to water, heat, shock, air, or other substances. 2 indicates that "Normally unstable and will readily undergo violent decomposition but does not detonate. Also: may react violently with water or may form potentially explosive mixtures with water."
Center White (Special Hazard) The standard's "Special Notice" field may contain a symbol denoting additional information about the substance(s), e.g., OX for oxidizers, SA for simple asphyxiant gases such as nitrogen and helium, and W for substances which react dangerously with water.
After this point, all squares are made up by Randall.
Center Left Green Number of digits in the street value ($/gram) (2) Describes the order of magnitude of the price (in USD) of one gram of the substance when sold illegally and informally. This is done on a logarithmic scale, with a '1' selling for $9/gram or less, a '2' selling for $10-$99/gram, and so on. As such this is the first of several squares where the number may presumably go to 5 or above (which is not allowed on the original Blue/Red/Yellow squares, as they do not denote strict numerical values). That said it's not immediately clear how substances which command <$1/gram would be handled.

Randall's example substance apparently sells for tens of dollars per gram (which would be similar to most common illicit drugs).

Center Right Dark Purple How much of a hassle it is to dispose of (4) While many things can be thrown in the trash with no additional procedures, substances that merit an NFPA 704 square often require additional procedures to avoid significant danger, damage to the environment, or hefty dumping fines. Biohazards that may carry diseases are often disposed of in special containers, and nuclear materials are notoriously difficult to safely dispose of. This square would be at least theoretically useful, though not as much as the actual disposal guidelines.

If the numbering here follows the scheme of the real categories, Randall's example substance is about as hard to dispose of as it gets. This matches the substance's rating of 4 for Blue and 2 for Yellow. Presumably it requires highly specialized handling or processing, and may also very bulky or awkward to store.

Bottom Left Lilac Number of federal agencies who want to know if you have any (3) In many countries, including Randall's home country, the USA, the government has agencies dedicated to controlling or limiting the use of regulated substances, due to their use as drugs, weapons, harm to the environment, etc. While any given substance might be of interest to one agency, something that is both an environmental hazard and a chemical weapon component could interest, for example, the EPA, Chemical Safety Board and the FBI Counter-terrorism Division.
Bottom Right Orange How many times you have to scrub your hands after touching it before they stop smelling weird (1) While the real NFPA 704 chart describes properties ranging from unsafe to potentially deadly, this square describes a minor but very real inconvenience. Some things are harder to wash off your hands than others, and, given that most people don't often work with dangerous substances [citation needed], this would be a more common, but less relevant, concern for many people.

In this case, the substance, or its residue, seems to be fairly easy to wash off. This is seemingly incongruous with its ratings in the Blue and Black squares (see below), though it's possible that this substance simply doesn't have a strong odor.

Bottom Black Number of times it's caused one of those terrifying lab accidents that chemists tell scary stories about late at night (2) This square might show how concerned and careful someone should be in handling the substance in question, especially if the number is more than one. However, it would be dependent not just on how inherently dangerous the substance is, but also on how commonly it occurs in labs. It's also vague as to what kind of accidents it has been involved in and what precautions therefore need to be taken. It could, for example, have caused some terrifying reaction, destroying things around it, or it could be very large and unwieldy and liable to crush people if handled improperly.

In this case, it seems the substance has caused two such accidents, presumably on account of its high health risk of 4 in the Blue square, and may also be linked to its hazardous disposal score of 4 in the Purple square.


[A diamond (a square on edge) is divided into 3x3 diamond squares. Each of the 9 squares have a unique color. All 8 squares along the sides have a large number written inside, in black except for in the black and the purple square where the number is written in white. The central square is white and have black text only. Each of the other eight squares have a label written on the outside with a curved arrow pointing to it from the label. Above it all is a heading:]
Know your extended NFPA hazard diamond:
[For each square the position and color is mentioned, from top to bottom in reading order. Then the text inside the square is given and then the label when there is one:]
[Red top square]
0 Flammability
[Blue top-left square:]
4 Health hazard
[Yellow top-right square:]
2 Instability/reactivity
[Green center left square:]
2 Number of digits in the street value ($/gram)
[White center square:]
(Special hazard)
[Purple center right square:]
4 How much of a hassle it is to dispose of
[Pink bottom-left square:]
3 Number of federal agencies who want to know if you have any
[Orange bottom-right square:]
1 How many times you have to scrub your hands after touching it before they stop smelling weird
[Black bottom square:]
2 Number of times it's caused one of those terrifying lab accidents that chemists tell scary stories about late at night

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Are we going to try identifying what material this is? 01:50, 28 June 2022 (UTC)

first one off the top of my head, aqua regia? 02:46, 28 June 2022 (UTC)Bumpf
Doesn't aqua regia score a 0 in reactivity? N-eh (talk) 03:23, 28 June 2022 (UTC)
Or maybe Aqua Velva? That would explain the orange square, although maybe it would be a number larger than 1. 22:49, 28 June 2022 (UTC)
My guess would be something radioactive, like uranium or plutonium. Clam (talk) 03:29, 28 June 2022 (UTC)
There are very, very few Health 4 / Fire 0 / Instability 2 compounds. The NIH database lists 4: nitrous oxide, phosphorus oxychloride, phosphorous trichloride, and thionyl chloride (although it's important to note these values aren't always standardized; some authorities consider phosphorus oxychloride to be Health 3, for example). Based on the street value and the number of US agencies who would be concerned about it, my guess is thionyl chloride, a useful industrial chemical which is also used in at least one meth lab synthesis pathway... AND highly regulated as a chemical weapon precursor (to both sulfur mustard and G-series nerve agents). Oh, and it is absolutely a Disposal Pain 4 candidate, too. Qalyar (talk) 04:52, 28 June 2022 (UTC)
Not sure what source you consulted for this? Nitrous oxide is 2/0/0/OX and phosphorus oxychloride is 3/0/2/W. The last two you mentioned are 4/0/2 but also carry the W (reacts with water) which is missing in Randall's sign. 01:04, 29 June 2022 (UTC)
This search tool from the NIH. I'll blame them for any weirdness (and admittedly, I was a bit surprised to see nitrous oxide at 4/0/2). Qalyar (talk) 01:54, 29 June 2022 (UTC)
It could be the drop ceiling - if it's even moderately unstable that would certainly make it a hazard; it would be a pain in the arse to dispose of; there are probably a few agencies with an interest building regs, etc. that would want to know about it. I'm not sure what kind of street price it would command, though. 16:20, 28 June 2022 (UTC)
It could be something that wouldn't normally be classified as a material, like a velociraptor. I'd think more government agencies would want to know about their existence in reality, but it's possible in this universe their existence is less atypical. Edda (talk) 00:03 29 June 2022 (UTC)
Velociraptors would be quite lightweight and extremely valuable, though, so I suspect the street value would be higher. 08:40, 29 June 2022 (UTC)

The center square is a free space, but if you win without it you get a special bonus prize. 04:18, 28 June 2022 (UTC)

Given Randall's fixation with velociraptors, is anyone else thinking the "dropped ceiling" may be a reference to the labs in Jurassic Park?

Possible. The first thing I had to think of was HalfLife (ie Black Mesa). Elektrizikekswerk (talk) 07:34, 28 June 2022 (UTC)
Since as a German I never heard of a dropped ceiling before, I automatically assumed it's a ceiling that drops on you. Ouch. 19:28, 28 June 2022 (UTC)
We call them "Zwischendecke" ;) Elektrizikekswerk (talk) 08:42, 29 June 2022 (UTC)
As an English speaker myself (rightpondian), I had to say I never knew the term before this comic. To me, they always were "suspended ceilings" (as, apparently, pretty much all the patents for them are, when I checked). Or maybe "false ceiling" but that might include no-gap re-lining to make a plaster ceiling look like it's wood. But "drop ceiling" (reminiscent of the "drop bear"!) is yet another thing our leftpodian cousins surprise me with. ;)
(Sometimes the gap itself is known to me as "crawlspace", though of course you rarely can physically crawl there, not being man-rated (nor ever having ventilation-ducts of convenient me-size, because we tend not to do that so much in the UK), and I've never felt I could escape (say) velociraptors by heading up there, but it's definitely where I "crawl" cables, every now and then, adding new network cables to any given office space, and I can tell you how dusty it gets up there. I've never thought it more than 'ambient' dust, as nice or nasty as that might be considered, but as I feed/thrown cables around from one edge of a room to another I find that it's best done at the end of a work day, and not just so I don't have to work around those who sit beneath...) 11:37, 29 June 2022 (UTC)

Does Randall watch Warsaw local news? Yesterday there was an article about an accident with dropped ceiling. Accident with dropped ceiling next day on xkcd gave me uncanny feeling. Tkopec (talk) 09:31, 28 June 2022 (UTC)

I was wondering whether the whole thing was inspired by the 2022 Aqaba toxic gas leak, that it was published well within a day of. Probably not (because 'too soon', especially with deciding what humour to add, assuming he started from scratch) but he might well have heard of it even as he was already mid-way through the drawing/publishing process and felt it ok to press ahead (perhaps modified to make it less likely to be directly associated in some way).
Not worth an in-explanation (or Trivia) mention, but saying it here as a dismissable aside. 13:58, 28 June 2022 (UTC)

The "Number of times it's caused one of those terrifying lab accidents that chemists tell scary stories about late at night -> 2" reminds me of the Things I Won't Work With category on Derek's Lowe blog, including famous Sand Won't Save You This Time article about dangers of chlorine trifluoride, with a few scary stories included. --JakubNarebski (talk) 11:04, 28 June 2022 (UTC)

The "smelling weird" one made me remember the one about thioacetone-- 12:53, 28 June 2022 (UTC)
How about the aliens going through the ceiling crawlspaces in "Aliens"? Barmar (talk) 17:46, 29 June 2022 (UTC)

"Weird lab where it's about the soda machine" example, from the Bourne Physics/Chemistry Building at Royal Holloway, University of London (but I'm struggling to find a source I can cite) had a story that was always told on "new student tours" / open days etc. There's a corridor there where an odd pattern of the floor tiles don't match, approx down the middle of most of one corridor, to the vending machine at the end of the hall, which also has 2 mismatched buttons. It's not 100% clear what the unlucky individual did to become highly radioactive, but he then allegedly decided he needed a drink. Later, the clean-up crew, after decontaminating the room where the accident occurred, could tell using a Geiger Counter exactly what route the guy took to the soda machine, including where he staggered - particular floor tiles were radioactive enough to remove and dispose of as "radioactive waste", replacing them with tiles that evidently didn't match the originals very well. Similarly, from the 2 mis-matched buttons on the machine, you can tell from what row/col the unfortunate victim ordered as his last drink. 02:58, 29 June 2022 (UTC)

I don't want to get involved in someone's edit-war, but I think the reasonings behind this edit are easily refutable:

  • all other squares have descriptions - yes, but all other squares have arrows to indicate an externalised description, there's no reason to believe that this would not have an arrow pointed at it from outside or inside, at a push. It may even be self-descriptive, but there's no reason to believe it isn't fully diagetic
  • parenthesis wouldn't be used for a symbol - but a strikethrough would? Because it is...
    • If anything, less ludicrous (potentially a strike against my final theory, mentioned below, which I will admit for completeness)
    • You would have better mentioned that it's big and entire words, not a diagraph/monograph abbreviation, but you didn't (and I think it wouldn't work as "SH"/whatever anyway, at any level of joke).
    • Parentheses aren't used for any other non-diagetic label, though we could argue the toss about whether they are the replacement for the arrow (which I think could have been drawn just as easily) and I think this aspect is a stalemate in this particular argument, but it's one I did consider when thinking about the merits of the various edits.
  • and "Special Hazard" is the square description synonym used in the non-Wikipedia reference link at the top of the table - not "Special Notice"? (The link may have changed since I first followed it, with interest, as we don't have these diamonds over here, we use Hazchem boards... nothing like seeing a bit of 3YE flammable liquid on the move! ...but whereve I first checked it certainly wasn't "Special Hazard".)

...I think it is intended as a rather clever self-referential joke. Why leave the square empty, except for the rather boring 'real' description? At least the other three standard sub-diamonds have some food for thought in their indicated values. Very unlike Randall to do nothing in that space when all kinds of real fun could have been had. I think I also believe (along with at least one other editor out there) that this is the particular fun that he decided to have with it. Much more believable than the alternative, IMO. (YMMV, HTH, HAND, ETLA...) 23:25, 2 July 2022 (UTC)

If it wasn't for the parentheses I would agree with you. The argument is far from a "stalemate" and the fact you would suggest it is leads me to think that you care more about advancing an implausible pet theory than providing a high quality explanation. 17:50, 25 August 2022 (UTC)
I don't know if it's just you, but there's been a spate of censorious editings recently. I don't much care, but it looks like someone who thinks they have the ultimate view on all articles without even the courage to put a username behind their changes. (Don't have a strong opinion myself, and I don't mind so much if articles are made less than explanatory, given someone else can always improve them again if they think there's something 'new' to add, even years down the line.) 05:29, 26 August 2022 (UTC)
Absolutely not. None of the even non-standard symbols are more than four capital letters long. If Randall had meant the text to be anything other than a description, he would have used SH. The link that calls the white square "Special Hazard" is http://www.ilpi.com/msds/ref/nfpa.html Furthermore, what exactly is the joke supposed to be, again? 00:33, 3 July 2022 (UTC)
(Isn't most of that already fully covered by 162.etc... New arguments are needed, or write it as maybe/maybe not. I think absolutes are unlikely to prove, either way.)
Some other editor said they changed the description of Special Hazard (not the transcripted contents, but the reality of the actual square) to "Special Notice", for apparently good reasons related to some link, IIRC, but maybe that's inconsistencies in how the standards-body documents it or something.
But whatever.... not my argument. 01:28, 3 July 2022 (UTC)
I agree with that this is a mistaken idea and should be removed from the explanation. 22:35, 3 July 2022 (UTC)
As it's being argued over again, with an absolutist (or maybe "absolutely not!"-ist) unilateral wish to remove all such speculation, I'm just gonna mention that 'unintentional' and intentional literalism is a recurring xkcd theme for depictions of symbolic pennants, whatever the actual degree of intention this time round. From "Ha ha... No, never actually thought to do that" through to "*sigh* - I shouldn't need to explain the whole joke, folks! You take this far too seriously[1], just enjoy the bits you understand...". If you go and pester Randall on Twitter/whatever and get his word that it's the former, then perhaps you can consign it to "confirmed not to be this", but then you'd be obliged to report the possibility in order to show the refutation itself, so probably counter-productive even if proven correct... ;) Leaving it as "it possibly might be..."/whatever the best wording, however, does not make any insistance that it is, but certainly adds something to the kind of person like me who likes to see what others have gotten from the comic (however wrong). 16:06, 14 July 2022 (UTC)
[1] Incidentally, I think I'd be right to say that sometimes we do! Often even! ^_^
I have proposed a compromise using small text. 16:23, 14 July 2022 (UTC)