Welcome to the explain xkcd wiki!
We have an explanation for all 2636 xkcd comics,
and only 66
(3%) are incomplete. Help us finish them!
Go to this comic explanation
|Extended NFPA Hazard Diamond|
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 explanation may be incomplete or incorrect: Created by a SUBSTANCE WORTH $500 IN STREET VALUE - Please change this comment when editing this page. Do NOT delete this tag too soon.|
This comic depicts an extension of NFPA 704, bringing it from 2x2 to 3x3 by adding 5 variously useful and humorous squares.
Squares and explanations
|| Comic text
|| Flammability (0)
|| [Real NFPA 704 square]. Denotes flammability. 0 indicates "materials that will not burn."
| Top Left
|| Health Hazard (4)
|| Real NFPA 704 square. Denotes the danger that the substance poses to living beings in ways other than flammability and reactivity. 4 indicates that "Very short exposure could cause death or serious residual injury even though prompt medical attention was given."
| Top Right
|| Instability/Reactivity (2)
|| Real NFPA 704 square. Denotes how easily the substance reacts with other substances. 2 indicates that "Normally unstable and readily undergo violent decomposition but do not detonate. Also: may react violently with water or may form potentially explosive mixtures with water."
|| (Special Hazard)
|| Real NFPA 704 square. Contains a symbol with additional notes on the substance. After this point, all squares are made up by Randall. 
| Center Left
|| Number of digits in the street value ($/gram) (2)
|| Describes the order of magnitude of the price (in USD) of one gram of the substance when sold illegally and informally. Most common illicit drugs would score 2 in this square.
| 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.
| Bottom Left
|| 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, 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, both the Chemical Safety Board and the FBI Counterterrorism Division.
| Bottom Right
|| 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 , this would be a more common, but less relevant, concern for many people.
|| Number of times it's caused one of those terrifying lab accidents that chemists tell scary stories about late at night (2)
|| The result of this square, although dependent on how much the substance is researched in labs, can show how scared someone should be in handling the substance in question, especially if the number is more than one. Though the description is vague, this number could show how easy it is to cause some kind of reaction of a terrifying magnitude with this substance.
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.
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.
|| This transcript is incomplete. Please help editing it! Thanks.
- Know your extended NFPA hazard diamond:
- [The diamond is divided into 3x3 squares.]
- Flammability: 0 (top, red)
- Health hazard: 4 (top-left, blue)
- Instability/reactivity: 2 (top-right, yellow)
- Number of digits in the street value ($/gram): 2 (left, green)
- (Special hazard) (center, white)
- How much of a hassle it is to dispose of: 4 (right, purple)
- Number of federal agencies who want to know if you have any: 3 (bottom-left, pink)
- How many times you have to scrub your hands after touching it before they stop smelling weird: 1 (bottom-right, orange)
- Number of times it's caused one of those terrifying lab accidents that chemists tell scary stories about late at night: 2 (bottom, black)
Is this out of date? .
Lots of people
contribute to make this wiki a success. Many of the recent contributors, listed above, have just joined
. You can do it too! Create your account here
You can read a brief introduction about this wiki at explain xkcd. Feel free to sign up for an account and contribute to the wiki! We need explanations for comics, characters, themes and everything in between. If it is referenced in an xkcd web comic, it should be here.
- There are incomplete explanations listed here. Feel free to help out by expanding them!
Don't be a jerk.
There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.
If you want to talk about a specific comic, use its discussion page.
Please only submit material directly related to (and helping everyone better understand) xkcd... and of course only submit material that can legally be posted (and freely edited). Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.
If you need assistance from an admin, post a message to the Admin requests board.