A lot of the organometallics are rather... interesting compounds to work with. The most famous (among those who care, anyway) is tert-butyllithium or t-BuLi. It is the textbook example of a pyrophoric substance, demonstrated to pretty much every chemistry major as an air-sensitive chemical requiring special handling (Syringe and cannula transfers, gas-tight septa, argon/nitrogen blankets, that kind of thing). Despite the inherent hazards of the stuff, it's widely used in the industry (hence widespread notoriety) to add butyl groups to an organic molecule (most organometallics are useful for this kind of carbon-carbon bond formation), and you can buy it by the - airtight - gallon canister.

There are, surprisingly (except to most organic chemists), even more dangerous compounds in the average organic chemistry lab. Along the pyrophoric line, many of the multi-methyl-metallics are violently pyrophoric (even compared to BuLi), including trimethylaluminum, dimethylzinc, and dimethylmagnesium. All of these are also extremely poisonous (anything these compounds can do to your wonder-drug-in-progress, they can also do to various key structures in your own body), with dubious honors reserved for dimethylmercury. Because many of these, especially the organoalkaline compounds, react violently with water, they also automatically rate at least a 3 on the "reactivity" scale.

When leads me to wonder, because I wonder about these things from the safety of my office chair in a completely unrelated field; just how bad can it get? Specifically, is there any compound with an accepted use in laboratory or industrial application that is nasty enough to max out the entire NFPA-704 diamond? The closest I can find is trimethylaluminum, at a 3-4-3 (heath-fire-reactivity). T-BuLi is a 3-3-4. I can't find NFPA data on straight diazomethane (which may be because nobody in their right mind ever works with the stuff in its pure gaseous form; it's always used in a dilute diethyl ether solution, and even then is never sold or shipped that way) but it would probably be a finalist, as the gas is acutely toxic, autoignites at room temperature, and detonates on standing (something for everyone!). I'm thinking that these two inorganic families - light alkyl-metallics and organo-polyazides - would be the most likely candidates to produce a compound so toxic, so flammable, and so readily reactive, yet so interesting to chemistry, that the NFPA would see fit to rate it, and would give it highest honors.

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    $\begingroup$ There's t-BuOOH but one source (cited by the Wikipedia stub article) says it's 4-4-4 while another source says it's 1-4-4... $\endgroup$ – BoltClock Feb 12 '13 at 8:26
  • $\begingroup$ @BoltClock and other sources have it at different values… it depends how it is conditioned (in solvent, or adsorbed on porous substrates, …). As the question say, noöne in their right mind would sell it in a form where it is 4-4-4 (and noöne would probably buy it, because it would hardly be usable!) $\endgroup$ – F'x Feb 12 '13 at 8:37
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    $\begingroup$ Diborane is a pleasant 4-4-3. Seriously, that stuff is nuts. Nice example of 3c2e bonding though. Hydrazine is also 4-4-3. $\endgroup$ – Richard Terrett Feb 12 '13 at 10:36
  • $\begingroup$ I found a MSDS for diazomethane but it is not a very good one. However, all signs point to 4-4-4. $\endgroup$ – Ben Norris Feb 12 '13 at 11:39
  • $\begingroup$ Tert-butylhydroperoxide looks promising. One nitpick (which doesn't disqualify it as I didn't require it) is that it doesn't react strongly to water (it gets its 4 for reactivity from its strong oxidation qualities and its propensity as a peroxide to explode spontaneously). You still can't use water to fight this fire, but you can use foam. $\endgroup$ – KeithS Feb 12 '13 at 18:24

Diborane. NIOSH gives NFPA 4-4-4-W:

NFPA 704 4-4-4-W


Answering my own question based on the comments, tert-butyl-hydroperoxide is at least one such chemical. As stated on this MSDS from a government website, it's a 4-4-4, with additional special warning of being a strong oxidizer. The only thing that it does not do that could make the 704 diamond any worse is react strongly with water. It is in fact water soluble, though marginally, preferring to float on top (and therefore traditional water-based fire suppression is ineffective, but foam/CO2 will work).

If anyone else can find a chemical that, in a form that is used in the lab or industrially, is a 4-4-4 that is a strong oxidizer and reacts strongly with water, that's pretty much "as bad as it gets" and they'll get the check.

  • $\begingroup$ There seems to be some question about the rating of tert-Butyl hydroperoxide. Perhaps in part because in practice it is never supplied or used undiluted? The NOAA page itself links to the ICSC which lists a 70% aqueous solution as 1-4-4-OX. $\endgroup$ – feetwet Dec 13 '16 at 2:51

Ethyl nitrite is rated 4-4-4 but it does not have anything on the white square. Pentaborane has a good 4-4-4-W. However it's not an oxidizer.

  • $\begingroup$ Wikipedia's article on pentaborane rates it a 3-3-2; not sure what form it's in for that rating. Anyway, source? If you can back up your pentaborane rating you'll get the check; it may not be an oxidizer, but a 4 for reactivity plus a "no water" hazard means it'll do practically everything else but. $\endgroup$ – KeithS May 4 '15 at 16:26
  • $\begingroup$ As for ethyl nitrite, that's been used as a cold remedy for centuries (though OTC sale was banned by the FDA in 1980 as being "not safe or effective"), and is rated a 2-4-4 by NIST. Notwithstanding a few doozies from the medical community and a mentality in previous generations that "if it tastes bad/hurts/makes you puke, it must somehow be good for you", anything nasty enough to get a Health-4 rating from the chemists would be a pretty obvious poison over on the medical side. $\endgroup$ – KeithS May 4 '15 at 16:39
  • $\begingroup$ NIOSH rates pentaborane 4-4-2, no W noted. $\endgroup$ – feetwet Dec 13 '16 at 2:48

It seems that diborane (see answer by feetwet) is the only compound rated with H4 F4 R4 code by NIOSH, though there are two substances lacking just a single point to join a 4-4-4-club:


Now I'm no chemist (I'm actually a biologist, with a science addiction) But as far as flammability and reactivity especially with water, I would assume some of the alkali metals, especially the heavier ones. Cesium in particular explodes on contact with water.

I would assume that any radioactive isotopes of it would be considered a huge health hazard, due to its analog nature with sodium and other lighter members of it's family.

On that thought, the end Actinides Uranium, Neptunium, and especially Plutonium are all highly hazardous for their radioactivity as well as being heavy metal poisons like lighter analogs such as Lead, Thallium, and Polonium (also lethally toxic due to radioactivity).

The fission metals (if you will pardon the term) are also pyrophoric due to decay heating and when divided will often spontaneously ignite. Admittedly these are all chemical elements, and the properties of a single element is no guarantee on it's action as part of a compound.

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    $\begingroup$ Many (most?) of the chemical elements have some pretty nasty properties, but most pale in comparison to what compounds made of fairly benign elements (in elemental form) can do. Zinc oxide is inert enough to slather your face with it, but dimethyl zinc violently burns in air with no ignition source. Mercury's fairly toxic on its own, but not all that "bioavailable" since the human body doesn't need any so it doesn't have any biochemical system to take it in. Dimethyl mercury, however, is so toxic a drop will kill you through your latex gloves. $\endgroup$ – KeithS Sep 2 '15 at 17:59

protected by Loong Oct 16 '17 at 16:17

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