Acute tear gas health hazards pointed by a French health report

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The French society of toxicology just published a report about “tear gas usage and its short and long term toxic effects”. L’Obs exclusively released this document.

By Emmanuelle Anizon

Published June 27th 2020 at 9 a.m., update 9:45 a.m.

A man throws a tear gas grenade back, in Bordeaux, December 5 2019. (NICOLAS TUCAT / AFP)

French society of toxicology-chemistry, Paris, published a report about “tear gas usage and its short and long term toxic effects”. 126 pages, over a year of hard work by Alexander Samuel. L’Obs was already the first magazine to publish a portrait of this maths high school teacher, PhD in molecular biology, and disheveled haired itching powder who accidentally leaded a healthcare team in doing blood and urine analysis on Yellow Vests Movement protestors in France, to detect presence of Cyanide in tear gas, and its consequence on public health.

“Tear gas harmfulness has already been largely questioned worldwide, but such a review had never been written, says André Picot, head of the Society Of Toxicology-Chemistry. Most of the studies are not publicly available because they are limited to the military domain. This work is of public interest”. Burning hot news, while protesters are drowning in tear gas clouds every day around the world.

What does this review say? Outside of technical biological analysis, which we will not comment out of complexity, this review describes tear gas effects and highlights the importance of cyanide in producing those effects. Each CS tear gas molecule that is absorbed will release two cyanide molecules. Absorption is not only respiratory, but can also be cutaneous.

This review describes the mechanism of cyanide poisoning (blocking the respiratory chain and causing an oxidative stress), and details what happens to the human body even at low dose intoxication. This molecule mainly affects brains, livers and kidneys. Eyes would also be affected (cataract…). It has an effect on central nervous system (headache, anwiety, dizziness, confusion, loss of consciousness, paralysis and even coma), on the respiratory tract (hyperventilation, tachypnea, dyspnea or apnea in extreme cases), on the cardiovascular system (hypotension, palpitations, arrythmia, tachycardia…), and even causing damage to thyroid, gastro-intestinal system (nausea, vomiting, diarrhea), musculo-skeletal system (muscular rigidity), liver… In New Jersey, the Department of Health calls protesters who are exposed to check up their livers and kidneys. “Why is nothing done in France? Asks Alexander Samuel. For political reasons, the scientific aspect is not explored.”

Deaths ?

In his review, Alexander Samuel reminds events in which CS could have caused death, directly or indirectly. “A link is often established by families and friends between tear gas exposure and death, but there are often discussions and there is rarely clear evidence. Recently in the United States, a young woman died from a pulmonary issue just after a demonstration with strong tear gas exposure. It was first said it might be due to tear gas, then discussed… We will probably never know. In France, Steve Maïa Caniço, a young man from Nantes drowned in June 2019 after falling in the Loire river during the music fest in June 2019. This happened just after a police charge with at least 33 tear gas grenades in les than half an hour. Enough to disorient someone… And yet, I regret no forensic analysis

Alexander Samuel hopes his work will trigger more awareness.

“What I have written interrogates. I would like other people to start working on answering those questions I raise.”

He still goes on interacting with scientists, sociologists, and Non-Governmental Organizations (like Amnesty International, who just launched a website dedicated to tear gas). He already teaches dangers of using tear gas through web conferences to police officers… from Chile.

Emmanuelle Anizon

Protection against tear gas


Tear gas is actually not a gas, but consists of solid particles in suspension. The average diameter is 8 microns, larger than the 3 microns of most filters block, so an A-P3 filter is enough to protect your airways.

To check if the mask is properly adjusted, block the air inlet where the filter is located with your hand and check if you can breathe: if it is the case, air passes through the sides and the mask is not adjusted tightly enough.

Résultat de recherche d'images pour "lunettes chantier étanches""

Protective goggles must be waterproof, to avoid the penetration of solid particles. However, it is better to take impact resistant glasses (risk of shots from rubber bullets), swimming pool glasses can cause damage by breaking.

film étirable manuel cast 15 microns 300 m x 450 mm

To protect themselves from skin penetration, some use plastic film, or put on gloves and waterproof clothing…

Extinguish pellets

Traffic cone
Pellet Trap
Campden tablets could be added to water for better efficiency

Post Exposure

After exposure, it is important to take a COLD shower to avoid opening of skin pores and letting the molecules in.
Clothing should be removed as soon as possible and then insulated or washed. In case of young children exposure, it may be useful to remove the clothes immediately and put on a survival blanket. Exposure should be minimized by removing contaminated clothing which may come into contact with the child, including that of adults nearby.

Post exposure products

We do not recommend the use of any of these products, we only list the products already used, recommended by some or existing.

CS is more irritating at high temperatures, and can only irritate in the presence of water (humidity, sweat, etc.). US soldiers use a decontamination technique which consists of drying the exposed area off, then applying decontaminant and washing it off.

In the field, many techniques have been developed, here are their advantages and disadvantages. We do not recommend the use of any of these products, and all drugs or medical devices should only be taken in the presence of a doctor.

Following exposure to tear gas, washing / rinsing using a Gaviscon® or Maalox® mixture with water in the presence of a doctor will reduce the burning sensation of the skin and mouth and prevent product penetration. An alcohol-free cleansing wipe can be used to remove as much product as possible from the skin. However, in case of excessive application, these products are irritants.
The use of Dacryoserum® in the presence of a doctor will only serve to dissolve the product in the eyeball, but in no case will prevent its penetration.
If rinsed with water, it must be cold in order to avoid an opening of the pores which would favor penetration of the product. The skin should be rubbed without irritating it. This action is to be carried out at the end of the day. Do not use soap at first. Take the opportunity to rinse your mouth and throat (by gargles) and eyes. Also rinse hair thoroughly before using a mild shampoo.
Eye and skin washed with Diphoterine® in the presence of a doctor, an aqueous solution containing amphoteric salts are recommended by some and rejected by others. Two views clash because, according to certain industrial hygiene specialists and certain chemists, this neutral pH product does not contain any particular or special products which can prove its usefulness.

Post-Cyanide exposure

To prevent risks due to exposure to cyanide by CS gas metabolism, André Picot, a famous french chemist, gave us dietary advice

The elements below are used in large quantities by the body to get rid of cyanide produced by the metabolism of CS gas, which ultimately leads to deficiencies and fatigue. We have completed the initial list of recommended foods. You can recover these elements by a simple and natural means: alimentation:

SULFUR: parsley, radishes, leeks, beans, lentils all foods containing natural sulfur garlic, onion, shallots, chives, cabbage, turnips, tap water, mineral water (especially those containing sulfates), wines (sulfites)…

B12: good quality calf’s liver (without hormones) meat, milk, kidneys, brewer’s yeast, edible seaweed, cod liver oil (in order of importance in intake: liver, caviar, mackerel, oysters, herring, beef , trout, tuna, sea bass, emmental, camembert, egg, plaice, fresh cottage cheese).

COBALT: cobalt food supplement in organic stores

In addition, when after manifestation you present extreme fatigue for several days, it may be useful to follow these dietary recommendations:

ZINC AND SELENIUM (anti-fatigue): broccoli, hazelnuts, nuts, almonds, chocolate, oysters, grilled wheat germ, veal liver, braised beef, dried shiitakes (mushrooms), grilled or oven-roasted squash seeds, crab, lentils, tartar or raw ground beef

How to craft a homemade respiratory system

A DIY system to avoid having your mask confiscated during a demonstration. A way of being effectively protected against tear gas, provided you master a breathing technique.
You have to breathe in with your mouth through the pipe, so that the air passes through the filter, and breathe out through your nose (without spitting air out of the pipe)

Material needed

You will need a P3 type gas filter cartridge (most often A-P3), strong and reinforced tape, a cutter and a pipe that must be cut to the appropriate length.

Crafting steps

1) Open the front of the filter and take the plastic plug
2) Make a hole in the plug using a cutter, to pass the tube and clamp it with a screw
3) Tape the whole abundantly, with tape covering both sides of the plastic cap
4) Add a rubber band and fix the cap on the filter.
5) Use the filter while breathing with the right technique

Preserving advice

Remember to unclog the bottom of the filter when you breathe, and to plug it back on when you have finished using it.
A glove placed at the end of the tube can be adjusted and prevent air from passing through the filter when not in use.

How to craft a homemade gas mask

Cut a transparent 2 Litre soda bottle as indicated
Glue a strip of rubber foam on the inside edge of the bottle
Glue a new strip of cloth over the foam rubber
Put a clinical mouth-cover in the neck of the bottle
Elastic to secure it to your head
Soak the mouth cover in vinegar before putting on the mask


Tuesday, November 5th, 2019

Emilien Urbach

Whistleblower. The young biologist from Nice highlights large doses of cyanide in the blood of demonstrators exposed to this chemical weapon.

“Cyanide in the tear gas used for law enforcement? Would the government poison the population? Unthinkable! It was the first reaction of Alexander Samuel, a math teacher and doctor of biology, when the yellow vest Julien Chaize, in April 2019, asked him to study this hypothesis. Six months later, the young scientist from Nice is convinced, significant doses of poison circulate in the blood of gassed demonstrators.

This conviction disturbs. On Saturday November 2, Alexander was taken into police custody on the grounds that he was implicated in a symbolic, bio-painted attack on a bank. He denies it but remains locked up for forty-eight hours. His home is searched. Its computer equipment and many documents are thoroughly inspected. A military manual from 1957, “on protection against combat gases”, is seized and destroyed.

Away, he observes the violence

This episode is apparently unrelated to his research on tear gas. In any case, the biologist has already compiled his work in a report. It will be published in the coming days by the Toxicology Chemistry Association, founded by André Picot, honorary director of the chemical risk prevention unit at the CNRS. The latter will co-sign the Alexander publication alongside other researchers and doctors.

There was nothing to suggest such a result when, at the beginning of spring, Alexander went for the first time to a demonstration of yellow vests. “I was suspicious,” he admits. In the Alpes-Maritimes, the far right was very present at the start of the movement and my environmental convictions were at odds with the demands linked to fuel taxes. Curious, however, he went to the rally organized on March 23 in Nice.

At a distance, he observes the violent police charges during which the head of Attac, Geneviève Legay, is seriously injured. Alexander does not attend the scene directly but he sees the street medics, these militant rescuers who intervene during the demonstrations, prevented from intervening and being arrested. Alexander films. He was immediately placed in police custody. It’s his first time.

“I was shocked,” says the scientist. The conditions of my detention, the lies of Emmanuel Macron and the prosecutor concerning Geneviève Legay made me stand in solidarity with the movement. He decides to gather everything that could make it possible to establish the truth and to pass it on to yellow vests who intend to seize the United Nations. Among them, Julien Chaize wants to convince him to look into the case of a demonstrator who, following an exposure to tear gas, displayed an abnormally high level in the blood of thiocyanate, molecule formed after the assimilation of cyanide by the liver.

This is an isolated case. Impossible for Alexander to see in it evidence of massive poisoning of the population. Incredulous, he participated in other demonstrations and observed the reactions of people exposed to the gases. Vomiting, irritations, disorientation, loss of consciousness … these fumes don’t just make you cry.

Alexander consults the scientific literature. The tear gas component used in France is 2-Chlorobenzylidene malonitrile. As it is considered a chemical weapon, its use is prohibited in the context of armed conflicts. Not for policing. For the biologist, the verdict is clear, this molecule, once present in the blood, releases cyanide. Several studies since 1950 confirm this. None said otherwise. But this poison is also present in cigarettes and a multitude of foods. Its dangerousness is therefore a question of dosage. How to measure it?

Alexander and three doctors in yellow vests then proposed to the demonstrators to have their blood analyzed to determine a level of thiocyanate. But this marker is not reliable enough. Cyanide must be quantified. However, the poison is only detectable in the blood for a few tens of minutes. Armed with a kit of tests, prescriptions and forms to be signed by the candidates for an exam, they decided to take blood and urine samples directly during the demonstrations of April 20 and May 1.

The results are edifying

The results of the first samples confirm the significant presence of cyanide, but do not give the precise dosage. On June 8, in Montpellier, the team perfected their protocol. Alexander, the three doctors and a few accomplices make themselves guinea pigs from their experience. They test their blood before the demonstration and afterwards. The results are edifying. Scientific community considers cyanide poisoning

Émilien Urbach

Alexander Samuel, the man who investigates tear gas used against “yellow vests”

Alexander, at a national yellow vest protest in Montpellier. (©Xavier Malafosse/Sipa Press / Xavier Malafosse)

PhD in biology, Alexander Samuel investigates dangers of tear gas, used massively in France against “yellow vests”. His method : entering in the tear gas cloud and analyzing blood and urine.

By Emmanuelle Anizon

Published on July 24th 2019 at 2.00 p.m.

We already saw him, multiple times, going into the white cloud and coming out minutes later, his long redhead mane in a hot mess, scarlet eyes and face, crying, coughing, tottering and almost fainting. Alexander Samuel, 34 years old, PhD in molecular biology, maths teacher in a public professional high school in Grasse, France, and philosophy dabster, would never have imagined breathing voluntarily tear gas in the middle of demonstrations. Neither crossing France with tubes of blood and urine in his car trunk, like a drug dealer, looking for a lab which could accept his cargo. Even less being convened by French justice for “endangering people’s live”. Him, whose only assumed violence consists of yelling regularly into a microphone, surrounded by his metal bandmates.

Alexander engaged by accident, on March 23rd 2019. On that day, the “politically very left wing tending” teacher comes as an “observer” to a “yellow vest” protest in Nice. He gets in touch with SOS UN, who are inventorying police brutality. “When I told them I was PhD in biology, they asked me if I could help them analyze the tear gas effects. They described me numerous symptoms : stomach ache, nausea, vomiting, muscle aches, severe migraines, but also loss of consciousness, pulmonary problems, heart problems, liver problems … “Yellow vests” had been hospitalized. They evoked potential cyanide poisonings. Cyanide ! I thought they were nuts ! But since there were many testimonies, I decided to dig it…”

Alexander Samuel, PhD in biology, experimenting during a « yellow vest » protest in Paris. (Bruno Coutier pour « l’Obs »)

Alex loves to dig. Already at the University of Nice, the brilliant PhD student half French half German had stood out for his propension to put his obstinate nose into affairs – misappropriation of subsidy, syndicate corruption, and other favoritism. “Alex is a researcher who finds, testifies Guillaume, a former comrade back in time. He accumulated evidences, gathered documents, recorded conversations. He combined methods of an investigator and a scientist”.

The teacher immersed himself into “literature”, as scientists say, reading everything that got published on the subject in scientific papers. And he methodically reports on his website. He discovers that “CS” gas used by police officers does not directly contain cyanide, but that one of its components, malonitrile, is metabolized into cyanide in the human body.

A public health issue

One can endure cyanide at low levels : smokers, people who eat cabbage, almonds or cassava. At higher doses, cyanide can cause hypoxia, lack of oxygen. It can kill in some cases, even if it did not happen yet in France. Alex explains :

“The person who got gassed endures some kind of strangulation. What is the health consequence of being strangled once a week ? We are told that tear gas are not dangerous, but we don’t know the long term health effects.”

The researcher spends days and nights on what he considers as “a public health issue : tear gas used nowadays massively by police forces, and not only on “yellow vests” : the “pont de Sully” ecologists, the young people at the music fest party in Nantes and people or businesses close to the demonstrations, all were exposed to tear gas. And even policemen, who are the first exposed !

Most of the time, they wear gas masks protecting them, but on June 28th, on the Sully bridge, a commander lost consciousness because of tear gas.

Read also : « Où est Steve ? », voilà LA question

Cyanide disappears in less than thirty minutes after tear gas exposure. But it leaves a marker in the body, thiocyanate, which can be detected during a few weeks after exposure. “I saw some “yellow vest” analysis results twice or even three times higher than normal values !” says Alex, who then contacts many toxicologists, doctors, scientists in France and abroad. Reactions are contrasted, some tell him he is totally wrong, like Jean-Marc Sapori, from the antipoison center in Lyon, and some encourage him to go on his “remarkable” work like André Picot, president of the Toxicology – Chemistry association, others even tell him

“Be careful, you are addressing a too dangerous subject”.

He calls a lot, and he gets called ore and more. A secret agent wants to give him confidential documents about tear gas victims during the Algerian war. Dozens of “yellow vests” want to testify, and send him their results.

“We are compiling their symptoms in a table, and we notice some new weird symptoms. For instance, many women, even menopaused, are having heavy menstrual bleeding”.

A doctor from the University Medical Center of Lyon writes him about a patient, gased multiple times, having a heavy liver disease from unknown cause : “I wonder if that could explain his pathology” she says.

How to prove the link between pathology and tear gas ?

What should we answer ? How could we prove irrefutably that link ? Since health authorities don’t address the issue and the interior ministry repeats “Move along, nothing to see”, Alex, three doctors – Renaud, anesthesiologist resuscitator, Josyane, generalist and Christiane, ophthalmologist -, nurses and some “yellow vests” decided to do blood uptake directly on demonstration site.

Christiane, ophtalmologist, member of Alex’s team.(©Xavier Malafosse/Sipa Press)

During his research, Alex found a Swiss company, Cyanoguard, selling kits to detect instant cyanide levels in blood : “It works like a breathalyzer. If the color turns purple, there is a dangerous level of cyanide. They are very serious, they published in the excellent journal of the Royal Society of Chemistry and FBI uses their tools!”. Alex and the doctors buy ten kits, 15€ each, and plan to send some other blood samples to a laboratory to make the classical thiocyanate analysis : “Combining both results, the reliability of our results will be reinforced”. And that’s how, on Saturday April 20th in Paris, “yellow vests” could see, in the middle of the smokes, spitting,  flashball shots and crowd movement, a little group equipped with helmets, glasses, syringes and tubes to do blood uptake on the pavement.

Results were deceiving : color change with cyanokit was difficult to interpret. “Cyanoguard told us “it’s positive” but I wasn’t sure”. Other surprise : the thiocyanate results, analyzed by the only French lab performing them in Lyon came back negative. “Even for smokers, which is impossible ! » says Alex sniggering. He often sniggers, giggling and narrowing his nose, like kids do. The teacher does not want to believe that those results are being faked voluntarily, but he thinks it would be appropriate to perform new analysis abroad in foreign “independent” labs.

Doctors are presented like murderers

On May 1st, during a very agitated demonstration in Paris, the little group backslides, this time in a building lobby, behind closed doors. “Yellow vests were waiting outside to duff us up”. The group was worried. In a background interior war inside SOS UN, Alex and the doctors left, a controversy started. Videos from blood uptakes were circulating on social networks where doctors were presented as murderers.

Read also : On a suivi des « gilets jaunes » devenus black blocs

Medias relay words from a “yellow vest” whose blood got collected, accusing the team for having abused of her weakness; the council of the Order of Doctors, asked about it, explains that it is not forbidden to do a blood uptake in the street, but it has to follow certain conditions. “Our blood uptakes were done respecting all security conditions, and everyone who gave his blood signed an informed consent” assure the three doctors from the team. A preliminary investigation is opened. At Alex’s high school, the director received messages calling him “illuminated”.

The team is doing blood analysis at the first floor of a Montpellier fastfood turned into a clandestine field hospital. (©Xavier Malafosse/Sipa Press / Xavier Malafosse

With this tempest, some in the groupe got scared and gave up. Not Alex, who decided to start from scratch with a reckless kernel of his team. They are reproached taking blood from others ? They will take their own blood. Not in the streets, but in the first floor of a fast-food in Montpellier, transformed into a clandestine field hospital (with the complicity and help of the manager, a “yellow vest” supporter”). That day, “l’Obs” was present, and the maker of the cyanokits too, he came in person to supervise the operation. This time, the cyanide level is quantified. Alex analyses :

“We are passing from a 0 or 0,1 mg/l value before tear gas exposure to 0,7 mg/l, the dangerousness threshold being at 0,5mg/l. It’s the sign that cyanide and tear gas are linked !”

But for toxicologists, the numbers from that non homologated kit will not be an official evidence. Alex went in person to a prestigious Belgian university to analyse the thiocyanate levels of the blood samples. 24 hours driving. The professors, very interested, received him for a long time but their laboratory declared itself incompetent. “They do not want to get involved, they know the French state will be confronting them” interprets Alex. Fear or not, he had to look somewhere else. Germans hesitated, sent him to a British lab which accepted. But when the tubes arrives, it was too late : “Pff… they are hemolyzed”, sighs Alex. Translate it : dated.

They risk correctional court

The series continued, but we will pass the episodes. We will just note a mass spectrometry analysis with distribution of urine collection pots to “yellow vests”. “They are very mistrustful. We collected only two samples, mine included” confesses Alex. Two, it’s very few. But, for 50€ each analysis, he couldn’t have paid much of them anyways. Including cyanokits, sending costs, analysis costs, lawyers, car transport, the teacher says he paid about 5000€, a big part of what he spared for his installation work in his new apartment.

He tells it with his unchangeable smile, nose and eyes narrowed. He says he doesn’t care. What he cares more about, is this preliminary investigation opened for “endangering people’s lives” and “prohibited interventional research”. Beginning of July, himself and three doctors got convoked by justice and thoroughly interrogated. They risk correctional court. They should quit ? Why go on in such a mess of hassles ? “We will not drop it until a serious epidemiologic study starts”. With the three doctors, Alex will call the High Authority of Health. Until then, he goes on digging.

About tear gas

Tear gas is a chemical compound causing eye and respiratory irritations. Like every chemical weapon, its usage is forbidden in the context of armed conflict by the international convention of Geneve (1993). Paradoxically it does not apply public order maintenance.

There are different kinds of gases. In France, police uses CS (chlorobenzylidene malononitrile) more and more massively, like the demonstrations showed it during the past years. The dangerousness of those gases is proportional to their concentration and depends on the conditions of their usage. Officially it is not lethal, but deaths have been reported by its usage in closed rooms, like during the Waco siege 1993 in the United States, or in Egypt and in Bahrein during population uprising.

In France, « CS concentration in grenades is 10%” tells us the general direction of the police, precising “It has been over 20 years that we are using this gas, if it was dangerous, we would have been the first victims, and police syndicates would have denounced it”.

Emmanuelle Anizon

What do you inhale when you breathe tear gas?

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23/12/2019 (UPDATED 18:16)
By Pierre Ropert

For months, protesters have been breathing in CS gas, which is found in tear gas canisters. But what are the consequences and dangers for an organism, while a researcher warns of possible formation of cyanide after breathing these gases?

Un manifestant tente d'échapper aux gaz lacrymogènes en se couvrant les yeux, lors du mouvement social du 5 décembre 2019.
A protester tries to escape tear gas by covering his eyes during the social movement of December 5, 2019.• Crédits : Bulent Kilic – AFP

After fifty years of use, one could imagine that a complete scientific documentation devoted to the effects of tear gas is available. However, in France, few studies have investigated that subject, and we must turn to Anglo-Saxon reports to learn a little more about the possible consequences of tear gas (CS gas) absorption.

CS gas, or 2-chlorobenzylidene malonitrile, however, has almost a century of existence. Invented in 1928 by American chemists Ben Corson and Roger Stoughton, whose initials it bears, it was synthesized in the 1950s in a version close to that which is still used today. It succeeds another gas, chloroacetophenone (CN), for its “virtues”: it is both less toxic and “its irritant effects are more pronounced and more varied”.

Its goal ? Immediate disabling effects 

During demonstrations, use of tear gas by the police usually results in scenes where demonstrators back up to escape that white smoke, coughing, crying and trying to protect their faces. And for good reasons, the effect of CS gas is almost instantaneous: it primarily affects eyes and causes, in just a few tens of seconds, an activation of the lacrimal glands. Once inhaled, it irritates the respiratory tract, triggering violent fits of cough which can go, according to the doses, up to vomiting. It can also cause severe itching or burning when it comes into contact with skin. These effects neutralize exposed people by forcing them to move, or by preventing them from resisting an attack.

Chemically, the effect of CS gas is simple to understand: its molecules bind to TRPA1 and TRPV1 receptors in our body involved in pain perception and responsible for detecting toxic products. The body then begins to produce mucus, watery eyes or even trigger coughs, in a violent reflex of rejection of what it considers toxic.

The action of riot control agents is almost immediate. Symptoms appear a few seconds after the toxic agent is dispersed and do only persist until a few minutes after the end of the exposure“, details researchers A. Gollion, F. Ceppa and F. May in a report entitled Ocular toxicity of chemical agents published by the journal Medicine and Armies

Potential long-term effects

Nausea, burning sensations, conjunctivitis, breathing difficulties, even fainting (including in law enforcement) … The main effects of tear gas are well known and dissipate quickly, once victims leave the tear gas cloud. However, long-term consequences of CS gas are very little studied in France, even though there is a substantial bibliography on the subject abroad. In 2017, a review of 31 studies in 11 countries, entitled Health Impact of Chemical Irritants Used for Crowd Control: A Systematic Review of the Injuries and Deaths Caused by Tear Gas and Pepper Spray, identified 5,131 injured people out of 5,910 people exposed to irritant gases having sought medical care, covering 87% of those affected. All in all, 9,261 injuries had been identified, most of them located on the eyes, skin, and the cardiopulmonary system. Although this study recalled that in vast majority of cases (98.7%) victims recovered quickly from their injuries, 67 people (1.3%) suffered permanent damage.

  • Eyes: conjunctivitis, keratitis and cataracts

Eyes are, in fact, the main target of tear gas. They are most quickly and directly affected by the fumes, whether they come from grenades or sprays. A priori, the impact of CS gas is quite low and sequelae disappear quickly over time. But a complete English-speaking documentation shows that, when the source of the gas is very close to the eyes, there can be complications, the most frequent of them being cases of conjunctivitis or blepharospasm (repeated blinking of the eyelids). In rare cases, long-term effects can be much more disabling: the doctor of ophthalmology at Saint Thomas Hospital in London noted in 1995 possible complications with inter alia infectious keratitis (lesions of the cornea), secondary glaucoma or cataract.

At higher concentrations, chemical burns with keratitis, loss of corneal epithelium and a permanent decrease in corneal sensation may be observed“, specifies the toxicological guide of the National Institute of Public Health of Quebec.

précise le guide toxicologique de l’Institut national de santé publique du Québec. “Since CS is a solid compound, particles may sink into the cornea or conjunctiva, causing tissue damage. The human eye is more sensitive to aerosolized CS compared to CS in solution. The overall ocular effects are more severe in individuals wearing contact lenses“.

  • Skin: itching, erythema and burning

Itching and redness caused by CS gas on the skin, if mostly benign, can also have serious consequences. A study from the Faculty of Medicine in Thessaly, Greece, published in 2015 and titled Exposure to the Riot Control Agent CS and Potential Health Effects: A Systematic Review of the Evidence Lists the Most Common Effects, Which May Last a few hours to two weeks, citing many other studies:

Common skin signs are erythema, skin rashes or blisters, skin burning sensations, skin irritation with or without pain, and burning.

Many cases of dermatitis or eczema, particularly in the case of allergic reactions, are also reported.

  • The respiratory system: a global weakening?

According to most studies, the respiratory system is certainly the most affected, in the long term, by the effects of CS gas. The toxicological guide of the National Institute of Public Health of Quebec states that after exposure to CS gas, the first symptoms (irritation of the throat, lungs, sneezing, cough, etc.) “may be followed by headaches, burning of the tongue and mouth, salivation and difficulty breathing (after some delay) and a feeling of oppression (at high concentrations)”.

A study by the University and Faculty of Medicine of Istanbul, Turkey, also looked at the long-term effects of tear gas on the respiratory system: it concluded that, in exposed subjects, certain disorders were 2 to 2.5 times higher than average, such as chest tightness, difficulty breathing, or winter cough. Subjects were also more susceptible to an increased risk of chronic bronchitis. Prolonged or excessive exposure to tear gas can also cause pulmonary edema.

If you did a lot of damage to the airways, it will stay. The mucosa is more susceptible to all infections, and viruses and bacteria will have a much more fertile ground for development. PHD Alexander Samuel

Des "street medics" accompagnent une manifestante touchée par des gaz lacrymogènes, lors de manifestations à Toulouse.
“Street medics” accompany a demonstrator affected by tear gas, during demonstrations in Toulouse.• Crédits : Getty

A lethal weapon indoors

In 2012, in Bahrain, law enforcement used tear gas to quell political demonstrations. The NGO Physicians for human rights reports that several women suffered a miscarriage after being exposed to tear gas and that an asthmatic man died. Some people are more vulnerable to the effects of these gases, such as children, the elderly, people with asthma and pregnant women.

Under certain conditions, CS gas can even be fatal. Tear gas canisters are in fact intended to be diffused in ventilated places, making it possible to avoid air saturation with 2-chlorobenzylidene malonitrile. But in a closed place, it would be possible to reach “the concentration of CS which would be lethal for 50% of healthy adults, estimated between 25,000 and 150,000 mg / m³ per minute” according to an estimate of the report published in 1989 in The Journal of the American Medical Association: Tear gas: Harrassing agent or Toxic chemical weapon?

When a tear gas canister explodes outdoors, the center of the gas cloud can reach a 2-chlorobenzylidene malonitrile concentration ranging from 2,000 to 5,000 mg / m³. Indoors, concentration therefore increases rapidly. In 2014, for example, in Egypt, tear gas canisters fired from inside a truck carrying prisoners killed 37 detainees.

A Notre-Dame-des-Landes, en 2018, une zadiste marche au milieu des gaz lacrymogènes.
In Notre-Dame-des-Landes, in 2018, a zadist walks in the middle of tear gas.• Crédits : LOIC VENANCE – AFP

Cyanide poisoning?

For several months, another concern has been agitating the demonstrators, first of all yellow vests, who denounce possible cyanide poisoning following inhalation of tear gas. This theory is advanced by Doctor Alexander Samuel: according to him, metabolism of CS after its absorption would lead to formation of this poison in our organism.

This hypothesis divides researchers who believe either that it is not possible to metabolize enough cyanide for the quantities to become dangerous, or that the methods of sampling in manifestation are not reliable.

For Alexander Samuel, the first argument no longer needs to be given the paradigm shift:

The problem today is that you no longer have to throw a grenade with a single pellet, with protesters 20 meters from the pellet. Nowadays at a music festival with Steve Maia Caniço for example, there are 33 grenades thrown in 20 minutes … It changes doses, and it changes exposures. These are much higher exposures, with much heavier effects on health and, in the long term, what worries me are the levels of cyanide which are still completely ignored, and which can cause liver cirrhosis, kidney stones, kidney problems and neurological problems, like Parkinson’s for example.

To overcome the skepticism of certain specialists, Alexander Samuel, PHD in biology, himself having believed having first believed in a “fake news”, is preparing a complete report, with a broad bibliography, which we were able to consult. He surrounded himself with other researchers under the tutelage of toxicology chemist André Picot. Honorary director at CNRS and president of the Toxicology-Chemistry Association, he is a major support:

CS is an organic molecule: it means that it contains carbon and hydrogen. These hydrocarbons make up the basic body. It’s a bit difficult for non-chemists to understand, but […] concerning the tearing effect, everything is depending on the release of a molecule, malonitrile. It contains three carbon atoms and two cyanide atoms linked to one carbon atom. This intermediate molecule is used to make syntheses in organic chemistry, it is tear gas and can be very toxic. When CS gas arrives in an aqueous medium, for example in the blood, the water will attach to it. This hydration will make this CS molecule, itself already unstable, even more unstable. It will thus be attacked by enzyme systems that we have in the blood, which will oxidize it. This will release the malonitrile [from the CS molecule, ie 2-chlorobenzylidene malonitrile, editor’s note] which in turn, still by oxidation, will release cyanide. In the end, for a molecule of CS gas, you release a cyanide molecule into the blood.

Once the molecule is released into blood, it will be assimilated by the body, explains André Picot: “This is what is called metabolization. It is, of course, subject to genetic control. And people are generally unequal when it comes to this metabolism. There may be people who will react very quickly to this product and have toxic effects of cyanide, while others will resist. This individual susceptibility is very important, because it explains why you have some who can be very sick and others who go up to the barricades every Saturday and don’t really have symptoms.

Un manifestant au milieu d'un nuage de gaz lacrymogène, lors des manifestations du 1er mai 2019.
A protester in the middle of a cloud of tear gas, during the demonstrations of May 1, 2019.• Crédits : Martin Bureau – AFP

Why is this cyanide dangerous? Because it blocks cellular respiration explains the toxicochemist, the process which makes it possible to supply energy to our organism. In doing so, it suffocates the cells essential to our survival:

There are three organs that are very sensitive to cellular respiration and these are the ones that work the most. There is the brain and therefore cerebral asphyxia begins first with headaches, fatigue, depression, etc. You have the heart because it is an engine and it needs fuel. So you are going to have cardiovascular problems, palpitations, you may be passing out, etc. And then there is another one which is also sensitive, it is the eye, the retina. The retina works a lot and it seems that in the case of cyanide it is the lens which takes a hit. We do not know exactly why, since it is not oxygenated.

The formation of cyanide after exposure to CS gas is not surprising. It has already been demonstrated and studied in animals, says André Picot:

In rodents, it is very well demonstrated that a molecule of CS gas, during its degradation, releases a molecule of cyanide. Critics of this release of cyanide from CS gas, say that in animal experiments there is only a small amount of cyanide, and that, moreover, nothing is proven in humans . They are a bit of bad faith because there have been some studies before. There aren’t many of course, compared to the experimental studies, that’s obvious. But the armies, the police, have precise data to which we do not have access. We would love to have access to this kind of data, that’s the challenge.

Once in the blood, however, cyanide can be metabolized by the body. And that’s for a good reason, it also exists in its natural state: we find it for example in cassava or oleander, and the body therefore knows how to protect itself from it. Smokers also absorb it regularly without it directly killing them. Our body is thus able to detoxify cyanide by adding a sulfur atom to it thanks to rhodanese, an enzyme present in saliva and in the liver. This creates thiocyanate, which is then eliminated by renal filtration in the urine. It is with this biomarker that we can determine the increase or not in cyanide levels … Without knowing its precise origin: consuming cassava the day before can for example distort the results.

It was first of all based on measurements of thiocyanate levels that Alexander Samuel and his team sought to determine if there is a risk for humans. The first results, taken from yellow vests demonstrators on the sidelines of the demonstrations, made it possible to discover levels of thiocyanates which, if they were not dangerous, remained abnormally high. A finding that led them to measure, with cyanokits, the level of cyanide directly in blood before exposure to CS gas, between five and fifteen minutes after exposure, then twenty minutes after exposure (which also triggered the opening of a preliminary investigation by the Paris public prosecutor’s office, despite the consent authorizations signed by demonstrators). These tests, carried out on nine individuals, made it possible to realize that the level of cyanide, after exposure to tear gas, reached levels above the danger threshold of 0.5 mg / L of blood (it is considered as lethal at 1 mg / L).

Sampling may seem small, but for Alexander Samuel it is not a problem in this case:

Statistical strength is necessary when doing epidemiology, for example if you want to link a symptom (cancer) with behavior (smoking). In the specific case of cyanide metabolism, it is not necessary to have such a statistical force since we study a mechanism and not a correlation. Medical “case reports” are only made on single cases, the study of the decontaminant used massively by the police, for example, is based on a study carried out on five gendarmes.

However, I have nothing against more results and verifications, if Paris Prosecutor’s Office tells us that it is closing the case concerning blood tests without consequences and that we have the right to do so without them considering such a blood uptake as “aggravated violence” and “endangering the life of others”, or if a competent authority decides to finally make a mass spectrometer available, for example. At the moment, we are completely blocked for field analyzes.

Faced with what he considers to be a public health issue, Alexander Samuel hopes that the work carried out, which will be published in a few weeks, will make it possible to apply “a precautionary principle” or, at least, “the training of security forces so that they can better understand the potential risks (not only that of cyanide) when they use these tear gas canisters.” Especially since the police are often the collateral victims of the effects of tear gas:

Chlorobenzylidene malonitrile and TNT? Little-known compositions

But besides CS gas, what exactly does tear gas canisters contain, and in what proportions? Their “recipe” remains a mystery: in France, we don’t know their exact composition. Two French companies supply the police, Nobelsport and Alsetex. When contacted, the first informed that “management does not wish to answer on this subject” and the second did not respond any more. You have to turn to the militant collective “Disarm them” to find a fairly precise portrait of the composition of a tear gas canister:

O-Chlorobenzalmalononitrile (CS): tear gas and irritant, it causes tearing and irritates the mucous membranes of the nose, throat and skin in general.
Coal: upon combustion, it turns into pure carbon.
Potassium nitrate (saltpetre): upon ignition, it releases large quantities of pure oxygen which fuel the combustion of coal.
Silicone: during the combustion of carbon and potassium nitrate, silicone forms drops of silicone dioxide which will be used to ignite the other components.
Sugar: fuel, it melts at 186 ° C, heats and vaporizes the chemical without destroying it. It also maintains combustion by oxidizing.
Potassium chlorate: oxidant. When heated, it releases a large amount of pure oxygen and turns into potassium chloride, which produces smoke.
Magnesium carbonate: potassium chlorate does not get along with acid (the mixture is explosive), magnesium chlorate maintains slightly basic pH levels, neutralizing any acid content caused by chemical impurities or moisture . When heated, it releases CO2, further dispersing tear gas.
Nitrocellulose : explosive fulminant. During combustion, it releases large amounts of gas and heat. Low in nitrogen, it also serves as a sticky binder to keep all the other ingredients homogeneously mixed.

In reality, talking about “CS gas” is a language gap: 2-chlorobenzylidene malonitrile is not so much a gas as a white powder which volatilizes in the air when the tear gas canister is triggered. Most of the components of a tear gas canister therefore aim to ensure the diffusion of CS gas, responsible for irritant and tear effects. “These are not toxic products at all in general“, specifies on this subject the chemist specialized in toxicology André Picot, president of the “Association Toxicologie-Chimie”. “Grenades are based on CS gas and the rest, afterwards, it’s for propulsion and stabilization, because it’s an unstable molecule “.

Alongside the “classic” tear gas canisters, whether hand-held or not, there is also a very special model of grenade, the GLI-F4, a deafening tear gas grenade with blast effect created by the company Alsetex. It uses 26 grams of TNT to produce an explosion while diffusing CS gas. It is notoriously known to be at the origin of several cases of mutilation and groups of lawyers have asked, so far without success, for its outright ban. The grenade has not been banned, but the government has said it will no longer be produced. PHD in biology Alexander Samuel, in the absence of data provided by Alsetex and Nobelsport, relies on the work “The Preparatory Manual of Black Powder and Pyrotechnics” by J. Ledgard to know the components of tear gas grenades in their American version:

The main known recipe involves the use of 45% ortho-chlorobenzylidene malononitrile [or CS, ndr], 30% potassium chloride, 14% epoxy resin, 7% anhydrous maleic acid and 3% 4, 7-methanoisobenzofuran-1,3-dione.

The researcher specifies that, overall, these products are not dangerous or have, a priori, similar and / or lesser effects than those already caused by CS gas under “normal” conditions of use. It is therefore indeed 2-chlorobenzylidene malonitrile which is the main chemical agent responsible for the reactions of the organism.

Finally, handsprays used by the police, make it possible to spray directly at demonstrators. Some models use a gas created from capsaicin, an active ingredient in hot peppers: where, on the Scoville scale, which measures the strength of hot peppers, the red Tabasco sauce is between 1,500 and 2,500 units, law enforcement aerosol cans amount to more than 5 million units …

In France, however, CS gas is favored over capsaicin. In 1998, the aerosols used by the police thus contained 5% of CS gas, when in the United States the dose is around 1%. In the absence of information, it is difficult to know today’s exact content of 2-chlorobenzylidene malonitrile in aerosols but in 1996, the British police, who had obtained aerosols supplied by the company Alsetex, conducted tests to ensure that the sprays acquired did not exceed 5% … before realizing that their concentration in CS was between 5.4% and 6.8%. Faced with complaints, Alsetex acknowledged, in a note in February 1997, that the company did not measure concentrations of CS gas, before committing to tightening controls, without it being possible to check whether protocols have been put in place since, for lack of answers.

In an article in Liberation, an executive from the company Alsetex nevertheless specified that the dosage of tear gas canisters obeys to official regulations which require that there be no more than 20% of CS in grenades. A concentration “2,600 times lower than the lethal dose”, according to the toxicological guide of the National Institute of Public Health of Quebec. In France, however, it is unclear whether the authorities verify the concentrations of CS gas emitted by tear gas canisters or aerosols. Our attempts to contact the gendarmerie to be put in touch with specialists in the subject remained unanswered.

In a report submitted to the European Parliament in 1999 entitled “An Appraisal of the technology of political control”, Dr Steve Wright, professor at The School of Applied Global Ethics at the University of Leeds in the United Kingdom and former director of the Omega Foundation, which worked with the European Commission to track the sales of technological weapons to authoritarian regimes, nevertheless noted that “the French gendarmerie did not keep statistics or records about CS in order to suggest that it is safe. “

Pierre Ropert