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Thread: How Tear Gas Works: A Rundown of the Chemicals Used on Crowds

  1. #1
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    How Tear Gas Works: A Rundown of the Chemicals Used on Crowds

    How Tear Gas Works: A Rundown of the Chemicals Used on Crowds





    Tear gas thrown by the US Border Patrol to disperse Central American migrants
    is seen near the El Chaparral border crossing
    in Tijuana, Baja California State, Mexico,
    on November 25, 2018.
    Credit:
    Guillermo Aria, Getty Images


    Before the tearing, the choking and the pouring mucus, tear gas burns. It causes searing pain in the eyes, skin, lungs and mouth?or anywhere it touches. ?It can be overwhelming and incapacitating. You can be forced to shut your eyes and cannot open them,? says Sven-Eric Jordt, an anesthesiologist at Duke University. And then comes the coughing and the nausea and the vomiting. What causes these chemicals to have such devastating effects on the human body?

    Jordt has studied tear gas for over a decade, but he doesn?t think tear gas is the best term for the weapon. First, he says as a technical point, they?re not gases; they?re powders that billow into the air as a fine mist. ?I think of tear gas as a pain gas,? he says. ?Because it directly activates pain-sensing receptors.? Weapons like sarin gas cause muscle paralysis that can lead to suffocation. These are designed to kill, while tear gas? purpose is to repel crowds through maximum misery. Specifically, all tear gas agents activate one of two pain receptors, TRPA1 or TRPV1, and can be classified into two broad categories based on which of those receptors they activate.

    The first category, TRPA1-activating agents, includes the chemical called 2-chlorobenzalmalonitrile or CS gas. This is one of the agents used by U.S. law enforcement and, according to a U.S. Customs and Border Protection spokesperson, is what CBP officers fired into crowds of men, women and children at the U.S. southern border on Sunday. ?A lot of children fainted. My daughter also got hit. There were pregnant women there and a lot of older men, too,? a witness told the Washington Post on camera on Monday.

    These agents are chlorine-containing compounds that blow into the air as a fine particulate. ?They are actually dispersed by burning and deposit on the skin or clothing and can persist for a while,? Jordt says. ?They chemically react with biomolecules and proteins on the human body,? which can cause a severe burning sensation.

    These agents are rarely lethal, Jordt says, but deaths have occurred in cases where they have been used improperly?like a canister fired directly into a crowd and causing head or body injuries, or into confined spaces where people cannot escape. Children are particularly at a high risk for injuries from these agents, Jordt says, because they are so small. ?They are shorter, and there are increased concentrations are near the ground. They also have a smaller body surface and lungs so the potential for injury is higher,? he says.

    CS gas is the most common of these TRPA1-activating agents but, recently, law enforcement has begun using a newer compound, says Rohini Haar, a doctor with Physicians for Human Rights and a public health scientist at the University of California, Berkeley. ?More and more, there?s a higher-level version called CS2 or sometimes CX,? she says. ?They [contain silicon] so that they can last longer in the environment and don?t disintegrate as quickly.? The result is a more harmful tear gas that can continue to affect an area for several days.

    There are two other TRPA1-activating agents used for riot control: CR gas (dibenzoxazepine) and CN gas (chloroacetophenone, also used in bear spray). Both are more potent than CS gas, Jordt says. During the Arab Spring protests, CN and CR gas were reportedly used alongside CS gas, sometimes to devastating effect. ?In the Arab Spring protests, a lot of miscarriages were reported in pregnant women who were exposed,? Jordt says. ?Probably due to shock and stress and the chemical exposure.?

    The second category of tear gas agents are pepper sprays and activate the TRPV1 pain receptor. These are mostly derived from capsaicin, the spice compound in chili peppers. There are two compounds in common use in this category: OC gas, a concentrated solution of natural capsaicin, and PAVA, a mix of synthetic capsaicin also used by U.S. Customs and Border Protection. ?This has fewer chemical or allergic reactions, but it?s also an oil so it?s much harder to get off and can last longer,? Haar says. ?It can also cause corneal abrasions if you?re shooting it directly into someone?s eyes.?

    Long-term effects from any kind of tear gas are not well known, Haar says, particularly if they are related to infrequent and brief exposure. However, Haar studied residents of the Aida and Dheisheh camps in the West Bank, Palestine, where people reported chronic breathing difficulty, rashes and pain, which the residents attributed to weekly tear gas exposure. ?And there?s evidence that [tear gas] can cause emotional trauma, which would have long-term impacts,? Haar says.

    Given the risk of injury or damage, Haar says that there are almost no scenarios where the use of tear gas makes sense for controlling crowds. ?I can see very few discrete situations where there might be a direct need for tear gas to protect public safety,? she says. ?One thing we see more and more now is tear gas causing panic, disorder and chaos. There?s mass deaths from stampedes because tear gas was used.? In 2015, police fired tear gas in a soccer stadium in Egypt in an effort to quell rowdy soccer fans. Twenty-five people died from suffocation or trampling.

    Similar stories of exacerbation made Jordt feel skeptical that tear gas is ever useful. ?I?ve seen in Germany in the 1980s and 1990s?the use of tear gas escalated the situation,? he says. In May of 1986, protestors responded to tear gas grenades with Molotov cocktails during a May Day demonstration in Berlin?s Kreuzberg neighborhood. ?I think [tear gases] cause grief, confusion and increase aggression,? Jordt says. ?And they are obviously not as safe as we think.?

  2. #2
    I'm not so sure about ALL tear gases acting on transient receptor potential-vanilloid type receptors, what about simple irritants such as chloroacetone, or acrolein? I could see haloacetones simply acting as vectors for hydrohalic acids on hydrolysis, and acrolein is just one of the more generally irritating, noxious aldehydes around. Although not in use by the filth or military due to both instability and toxicity, but either will still send one coughing, spluttering and swearing well enough.

  3. #3
    Bluelighter atara's Avatar
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    Yeah, the way I mentally classify tear gases is, they are either ligands for TRPV1, by binding to the capsaicin-site -- and these are often called "pepper spray" because they are in some cases derived from pepper -- or they are electrophiles and usually Michael acceptors, which includes bromoacetone, phenacyl chloride, chlorobenzalmalononitrile, et cetera.

    The electrophiles are more commonly called "tear gas" but I've always found it sort of evil that they are approved for use on people. While tests have not found any strong evidence of mutagenicity, it's obvious from a glance at the molecular structure of CS gas that it is capable of alkylating DNA. It's just a matter of exposure. The article classifies these as "TRPA1 activators", which I assume happens downstream from the primary effect, which is tissue damage.

    The capsaicinoids I always thought were pretty harmless, but it turns out they can cause corneal abrasions due to swelling of the eye.

    Overall using chemicals on people is doubleplusbad, imho.

  4. #4
    Depends on the potency of the capsaicinoid.

    Resiniferatoxin for example, a hyperpotent capsaicinoid (well, TRPV1 activator), coming from certain plants in the genus Euphorbia (well known for packing noxious chemicals, phorbol esters usually. Some, such as the Manchineel tree, are so virulent, that in the case of that tree, caribbean natives would execute a particularly despised foe by tying them to the trunk and waiting for it to rain. The water washing off the leaves being so corrosive due to traces of sap in it, that the unfortunate poor bastard would literally be slowly flayed alive)

    Anyhow, resiniferatoxin, has a potency in the BILLIONS of scoville units, and along with the related tinyatoxin (which I confess I was surprised to find, wasn't the Buthid scorpion venom constituent I expected before reading of it), are so damn potent they quite literally burn out nociceptors, causing massive calcium influx and subsequent excitotoxicity. Potentially useful I should think, given how selective such ligands are for nociceptive fibers..say, you give someone both a local, and an opioid painkiller, and then administer resiniferatoxin in suitable concentration to the nociceptive nerve fibers supplying an area afflicted with intractable pain, selectively fry TRPV1-bearing nerve endings, could be a useful potential remedy for pain in certain circumstances. We already use the likes of capsicin ointment or patches for such uses, but why not a far more effective version, used of course by medical professionals, with the right care for the patient, spit-roast their nerve endings causing pain to the site they suffer at.

    As for capsaicinoids and eyes, don't forget there is a solvent to dissolve it to allow them to be sprayed also present, such as MEK, which presumably isn't a nice thing to have sprayed in one's face. I've gotten acetone in a minor skin nick or on a graze before and it stings like buggery. I'd sooner not be sprayed in the face with any teargases, but neither would I want MEK/MiBK alone thrown in my face. I should imagine the delivery vehicle itself would have negative effects on the eye.

    I've had my experience with tear-gases, making and testing them as a kid was quite enough (not directly in the face, just being in an enclosed area with the vapours of chloroacetone and acrolein. Plus one unintended flash-boil of chloroacetone during synthesis, aerosolizing the whole lot right next to me. I'm surprised you didn't hear a deafening torrent of multilingual profanity and blasphemies some 19-20 years ago from wherever you are.

  5. #5
    Bluelight Crew polymath's Avatar
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    Chloroacetone isn't completely water soluble, so it will probably end up deeper in the lungs when inhaled than things like acrolein, and stays there producing HCl and corroding stuff... This is probably the reason why it's not used as a riot control agent anymore.

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    I can see why you would wan't to go after someone who sprayed you with any of those gases.

  7. #7
    Neither are too stable either, best stored over calcium carbonate. But easy and cheap to produce, so smaller quantities can be produced on a suitable time basis to refill a container.

    And chloroacetone WILL drop a pair of noxious pikey bastards intent on mugging you then kicking your face in for a laugh afterwards, before they have chance to swing a punch in that nasty, tight little dark alley at night.

    One blast in their ugly mug is all that's needed. Granted yes, it's toxic, but it could have been worse. Could have been acrolein they got hit with. But as far as I'm concerned, if some little subhuman excuse for piece of constipated faecal matter, is prepared to attack me, without provocation, to take what belongs to me without permission, and more than likely kick my head in if they managed the fight without being harmed themselves; well then, they have just forfeited any and all sympathy on my part.

    The only important thing, is that a corpse isn't left behind. Otherwise, they brought it on themselves, and if they are left rolling around on the floor, clutching their face, spasming and trying to scream, whimpering like a whipped BDSM-male-whore being repeatedly kicked in the bollocks....too bad. Shouldn't have opened up hostilities. Because I will end them.

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