Sauvetage par inhalation de sulfure d'hydrogène (gaz d'égout), de cyanure et de gaz toxiques¶

Les numéros d'urgence diffèrent selon les pays. Cette page utilise le 911, le numéro des États-Unis et du Canada. De nombreux autres pays utilisent le 112, 999 ou un autre numéro. Trouvez le numéro de votre pays.

Inhaling a high concentration of an industrial, agricultural, or household toxic gas: especially hydrogen sulfide ($H_2S$ / sewer and manure gas), hydrogen cyanide ($HCN$ / structural fire smoke and industrial cyanide), chlorine or chloramine gas (mixed household bleach cleaners), anhydrous ammonia, or phosgene: causes life-threatening respiratory failure or instantaneous cellular asphyxiation within seconds. Even more tragically, toxic gas incidents routinely kill more would-be rescuers than original victims: when a worker, farmer, or family member collapses at the bottom of a manhole, septic tank, manure pit, ship hold, or basement, coworkers or relatives who rush in holding their breath without a Self-Contained Breathing Apparatus (SCBA) are knocked unconscious by a single breath of gas and die right beside the person they tried to save.

This guide provides step-by-step field rescue and clinical protocols aligned with directives from the World Health Organization (WHO), the United States National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), the Centers for Disease Control and Prevention (CDC), and the UK Health Security Agency (UKHSA). Enforcing the strict confined-space no-entry rule, understanding hydrogen sulfide olfactory paralysis (why you stop smelling rotten eggs just before a lethal breath), administering 100 percent high-flow oxygen, and delivering immediate hydroxocobalamin (Cyanokit) for cyanide saves lives.

Fais ça maintenant¶

If you see someone collapse inside or near a manhole, sewer line, septic tank, farm manure pit, grain silo, tank car, chemical room, smoky room, or poorly ventilated bathroom where cleaners were mixed:

STOP: NEVER enter a confined space, pit, basement, or gas cloud without an SCBA: Even if the collapsed person is your child, spouse, or coworker, do not go down the ladder and do not try to hold your breath and run in. A single breath of concentrated hydrogen sulfide ($> 700\text{ to }1,000\text{ ppm}$) or hydrogen cyanide knocks an adult unconscious in 1 to 3 seconds ("knockdown"), and filtration gas masks or wet cloths over your face provide zero protection in oxygen-deficient or high-concentration atmospheres. Only firefighters equipped with positive-pressure Self-Contained Breathing Apparatus (SCBA) and a tethered retrieval winch can enter safely.
Evacuate yourself and others upwind and uphill immediately: Move at least 30 to 100 meters (100 to 330 feet) upwind and to higher ground. Hydrogen sulfide ($H_2S$), chlorine ($Cl_2$), and phosgene ($COCl_2$) are heavier than air and pool in low-lying trenches, basements, sewers, and valleys. If toxic gas was generated indoors (for example, by mixing bleach with ammonia or toilet bowl acid in a bathroom), get everyone out of the house to fresh outdoor air immediately and leave doors open on your way out.
Appelez immédiatement votre numéro d'urgence local pour les pompiers/sauvetage en espace confiné HAZMAT : Appelez le 911 aux États-Unis et au Canada, le 112 dans l'Union européenne ou le 999 au Royaume-Uni (ou consultez notre numéros d'urgence annuaire). Dites clairement au répartiteur : * "Espace confiné / effondrement de gaz toxiques : victime dans [égout / fosse à fumier / sous-sol / déversement de produits chimiques]. Envoyez aux pompiers un HAZMAT avec un ARI et un antidote au cyanure (hydroxocobalamine)."*
Récupérez une victime uniquement si vous pouvez le faire depuis l'EXTÉRIEUR de la zone de danger : Vous ne pouvez retirer une victime que si elle porte déjà un harnais de sécurité attaché à un treuil/trépied mécanique externe à l'extérieur du trou d'égout, ou si elle est allongée dans une porte ouverte où vous pouvez accéder à l'air extérieur propre au vent sans franchir le seuil.
Une fois que la victime est à l'air frais, enlevez les vêtements extérieurs et vérifiez sa respiration : étant donné que des gaz comme le sulfure d'hydrogène et le cyanure d'hydrogène emprisonnés dans les fibres des vêtements continuent de dégager des gaz sur le visage de la victime et du secouriste, retirez rapidement la veste extérieure, la chemise et le pantalon de la victime à l'air libre. Vérifiez la respiration normale :
Si vous ne respirez pas ou si vous avez seulement le souffle coupé : commencez des compressions thoraciques avec les mains uniquement (RCR) ou utilisez un masque-valve-sac (BVM) connecté à 100 % d'oxygène. NE JAMAIS pratiquer le bouche-à-bouche direct sur une victime au cyanure ou au sulfure d'hydrogène, car son haleine expirée contient des gaz toxiques qui peuvent empoisonner le secouriste.
En cas de respiration : placez-les dans une position confortable (tendu droit en cas de toux/respiration sifflante due au chlore/ammoniac, ou sur le côté en position de récupération s'ils sont somnolents) et administrez 100 % d'oxygène à haut débit via un masque sans recycleur dès l'arrivée des secours.
Rincez les yeux et la peau brûlants à l'eau courante pendant 15 minutes : Si des gaz irritants (chlore, ammoniac, dioxyde de soufre, fluorure d'hydrogène) brûlent les yeux ou la peau humide, rincez continuellement à l'eau courante propre ou à une solution saline normale pendant 15 minutes (voir blessures aux yeux et brûlures graves et rinçage chimique).

Pourquoi 60 % des victimes dans les espaces confinés sont les sauveteurs et pourquoi votre nez vous ment

Selon les enquêtes du NIOSH et de l'OSHA aux États-Unis, plus de 60 % de tous les travailleurs qui meurent dans des accidents liés au sulfure d'hydrogène, aux fosses à fumier et aux asphyxiants en espace confiné sont les sauveteurs non autorisés qui sont intervenus pour retirer le premier travailleur effondré. De plus, ne vous fiez jamais à votre odorat pour juger de la présence de sulfure d'hydrogène ($H_2S$) : alors que de faibles niveaux non mortels de $H_2S$ (0,01 à 30 ppm) sentent fortement les œufs pourris, dès que la concentration dépasse 100 à 150 ppm, le gaz paralyse instantanément votre nerf olfactif (fatigue olfactive). L'odeur d'œuf pourri disparaît soudainement complètement, vous faisant croire que l'air s'est purifié juste avant qu'une seule respiration à 500 à 1 000 ppm ne provoque un coma instantané et un arrêt respiratoire.

Emergency field rescue and toxic gas triage flowchart¶

flowchart TD
    Start["Victim Collapsed or Gasping in Confined Space, Sewer, Manure Pit, Smoke, or Chemical Cloud"] --> Location{"Où se trouve actuellement la victime ?"}

    Location -->|Inside manhole, pit, tank, silo, basement, or dense gas cloud| StayOut["NE PAS ENTRER SANS ARI<br/>Appelez le 911/112/999 pour le service d'incendie HAZMAT Rescue<br/>Allumez les ventilateurs d'extraction externes ou utilisez un treuil à harnais externe UNIQUEMENT à partir d'un air sûr."]

    Location -->|Already rescued into fresh upwind outdoor air| Decon["Strip outer gas-trapping clothing in open air<br/>Check responsiveness and breathing"]

    StayOut -->|Firefighters with SCBA extract victim to fresh air| Decon

    Decon --> BreathCheck{"Is the victim breathing normally?"}

    BreathCheck -->|No: Apneic or Agonal Gasps| CPR["Start Hands-Only CPR + Bag-Valve-Mask (BVM) with 100% O2<br/>NEVER perform direct mouth-to-mouth rescue breathing"]
    BreathCheck -->|Yes: Breathing spontaneously| HighO2["Administer 100% High-Flow Oxygen (Non-Rebreather Mask)"]

    CPR --> GasID{"Identify Gas Mechanism by Scene & Symptoms"}
    HighO2 --> GasID

    GasID -->|House/building fire smoke, jewelry/electroplating shop, industrial nitrile;<br/>soot in mouth, coma, seizures, shock, Lactate > 8-10 mmol/L| Cyanide["Suspected Cyanide (HCN) + Carbon Monoxide Poisoning<br/>Immediate IV Hydroxocobalamin (Cyanokit 5 g IV over 15 min)<br/>+ Sodium Thiosulfate (12.5 g IV) + 100% Oxygen"]

    GasID -->|Sewer, septic tank, manure pit, oil/gas sour crude, geothermal;<br/>sudden 'knockdown' collapse, blackened silver coins/jewelry| H2S["Hydrogen Sulfide (H2S / 'Sewer Gas') Poisoning<br/>100% High-Flow Oxygen + Immediate Intubation if comatose<br/>Supportive ICU care (Nitrites / Cobinamide per toxicologist)"]

    GasID -->|Mixed household bleach + ammonia or acid cleaner, pool chlorine,<br/>or industrial tank leak; immediate choking, coughing, stridor, wheezing| Irritant["Water-Soluble Irritant Gas (Chlorine, Chloramine, Ammonia)<br/>Flush eyes/skin 15 min; sit upright; humidified Oxygen<br/>Nebulized Albuterol + Nebulized 2%-3.75% Sodium Bicarbonate (for Chlorine)"]

    GasID -->|Welding on chlorinated solvents (brake cleaner), Teflon overheating,<br/>or silo grain gas (NO2); mild early cough -> severe pulmonary edema 4-24h later| DelayedGas["Low-Solubility Irritant Gas (Phosgene, Nitrogen Dioxide)<br/>MANDATORY 24-Hour Hospital Observation even if feeling fine now<br/>Strict physical rest; PEEP / CPAP for delayed pulmonary edema"]

Pathophysiology of the "Cellular Asphyxiants": Cyanide ($HCN$) and Hydrogen Sulfide ($H_2S$)¶

Unlike choking on food (which blocks air from entering the windpipe) or drowning (which fills the lungs with water), Hydrogen Cyanide ($HCN$) and Hydrogen Sulfide ($H_2S$) are "chemical / cellular asphyxiants" (also called knockdown gases). When you inhale $HCN$ or $H_2S$, your lungs are still full of oxygen and your red blood cells are still carrying plenty of oxygen through your arteries: but your body's cells are chemically blocked from using that oxygen, causing your brain and heart to suffocate from the inside out in seconds.

How Cytochrome c Oxidase Inhibition stops cellular respiration¶

Inside the mitochondria of every human cell, the final step of aerobic energy production (oxidative phosphorylation) relies on the enzyme Cytochrome c Oxidase (Complex IV of the electron transport chain), which contains a central ferric iron ($Fe^{3+}$) and copper core that transfers electrons to oxygen ($O_2$) to make ATP (the fuel that keeps brain neurons and heart muscle beating).

Instantaneous Iron Binding: Both cyanide ($CN^-$) and hydrosulfide ($HS^-$) ions bind with ferocious affinity directly to the ferric iron ($Fe^{3+}$) atom inside mitochondrial cytochrome c oxidase.
Complete ATP Shutdown and Lactic Acid Explosion: With Complex IV locked shut, mitochondria can no longer consume oxygen or produce aerobic ATP. Desperate for energy, cells switch exclusively to emergency anaerobic glycolysis, which produces only a tiny fraction of the needed ATP while dumping massive quantities of lactic acid into the bloodstream (serum lactate rapidly spikes above 8 to 10 mmol/L).
Why Venous Blood looks "Cherry Red" (Arterialization of Venous Blood): Because the body's tissues cannot extract oxygen out of passing red blood cells, the blood returning through the veins back to the heart is still nearly 90 percent to 95 percent saturated with oxygen (instead of the normal 70 percent venous saturation). When nurses draw a venous blood sample from a cyanide victim's arm, the venous blood looks startlingly bright arterial red, and standard fingertip pulse oximeters ($SpO_2$) read a falsely reassuring "98% to 100%" even while the patient is dying of cellular hypoxia.

Master diagnostic comparison of Industrial, Agricultural, and Household Toxic Gases¶

Gas & Chemical Formula	Common Sources & High-Risk Scenes	Odor, Density & Physical Clues	Toxicological Mechanism	Classic Clinical Presentation	Definitive Antidote & Hospital Management
Hydrogen Cyanide ($HCN$) & Cyanide Salts	Structural house/building fire smoke (burning wool, silk, polyurethane foam, nylon, plastics, melamine), gold/silver mining, electroplating, jewelry cleaning, acetonitrile nail remover, sodium nitroprusside, apricot/cassava pits.	Bitter almonds odor (detectable by only 40%, 60% of people genetically); lighter than air ($HCN$ gas). Soot around mouth/nose in fire victims.	Binds $Fe^{3+}$ in mitochondrial Cytochrome c Oxidase $\rightarrow$ halts cellular oxygen use $\rightarrow$ fulminant anaerobic lactic acidosis.	"Knockdown" collapse within seconds at high gas levels; confusion, gasping tachypnea followed by apnea, seizures, coma, cardiovascular collapse/bradycardia, and Serum Lactate `>= 8 to 10 mmol/L`.	1. 100% High-Flow Oxygen. 2. IV Hydroxocobalamin (Cyanokit 5 g IV over 15 min) (binds cyanide to form harmless Vitamin B12 excreted in urine). 3. IV Sodium Thiosulfate (12.5 g IV).
Hydrogen Sulfide ($H_2S$ / "Sewer Gas" / "Sour Gas")	Sewers, septic tanks, cesspools, underground utility vaults, agricultural liquid manure pits, petroleum/natural gas ("sour crude") refineries, paper mills, tanneries, hot springs/volcanic vents, mixing toilet acid with sulfur products ("detergent suicide").	Rotten eggs odor at low levels (`< 30 ppm`), suivie d'une paralysie complète du nerf olfactif au-dessus de 100 à 150 ppm ; plus lourd que l'air (coule dans les fosses) ; noircit les pièces de cuivre et les bijoux en argent dans les poches de la victime.	Binds $Fe^{3+}$ in mitochondrial Cytochrome c Oxidase (identical to cyanide) + direct corrosive mucosal injury to eyes and alveoli.	Low levels (10 to 100 ppm): "Gas Eye" (painful keratoconjunctivitis, gritty eyes, halos around lights) + cough. High levels (`> 500 to 1,000 ppm`): Single-breath "Slaughterhouse Sledgehammer Knockdown" (instant coma, seizures, apnea, and cardiac arrest).	1. Strict SCBA Confined-Space Rescue. 2. Strip clothing & give 100% High-Flow Oxygen / Intubation ($H_2S$ dissociates faster than cyanide with $O_2$). 3. IV Sodium Nitrite (300 mg) or Hydroxocobalamin if given immediately (consult Poison Control).
Chlorine ($Cl_2$) & Chloramine ($NH_2Cl$) Gas	Mixing household sodium hypochlorite bleach with Ammonia ($\rightarrow$ Chloramine gas) or with Acid toilet bowl cleaner / vinegar / muriatic acid ($\rightarrow$ pure Chlorine gas); swimming pool chemical rooms; water treatment plant leaks.	Pungent, suffocating bleach/swimming-pool odor; greenish-yellow haze at high concentration; Chlorine is 2.5x heavier than air.	Intermediate water solubility: Dissolves in airway moisture to form Hydrochloric Acid ($\text{HCl}$) and Hypochlorous Acid ($\text{HOCl}$), burning from the throat down to the alveoli.	Immediate violent coughing, choking, burning eyes/throat, retrosternal chest pain, laryngospasm (stridor), severe bronchospasm (wheezing), and acute non-cardiogenic pulmonary edema.	Evacuate to fresh air; flush eyes 15 min; 100% Humidified Oxygen; Nebulized Albuterol for wheezing + Nebulized 2% to 3.75% Sodium Bicarbonate (4 mL) to neutralize airway acid.
Anhydrous Ammonia ($NH_3$)	Agricultural fertilizer tanks, industrial cold-storage/ice-rink refrigeration plants, methamphetamine labs, industrial cleaners.	Fiercely pungent, suffocating ammonia odor; lighter than air (unless cold pressurized liquid aerosol cloud, which hugs the ground).	High water solubility: Reacts instantly with moisture on the eyes, mouth, and upper airway (larynx/trachea) to form caustic Ammonium Hydroxide ($\text{NH}_4\text{OH}$) alkali burns.	Immediate upper airway catastrophe: Blinding corneal liquefaction burns, massive swelling of the lips/tongue/epiglottis, hoarse voice, high-pitched inspiratory stridor, and rapid upper-airway suffocation.	Flush eyes and skin with copious water for at least 15 to 30 minutes; early endotracheal intubation (before throat swells shut completely); humidified $O_2$ and bronchodilators.
Phosgene ($COCl_2$) & Nitrogen Dioxide ($NO_2$ / "Silo Filler's Disease")	Phosgene: Welding, brazing, or heat stripping metal cleaned with chlorinated brake cleaner (tetrachloroethylene / trichloroethylene); burning Freon/refrigerants. Nitrogen Dioxide ($NO_2$): Freshly filled farm grain/corn silos (first 2 weeks); diesel exhaust; nitric acid spills.	Phosgene: Smells pleasantly like freshly mown hay or cut green corn. $NO_2$: Reddish-brown heavy gas at bottom of silos with sharp bleach-like odor.	Low water solubility: Because they do NOT dissolve in the wet nose or throat, they cause minimal early coughing, allowing the victim to inhale them deep into the alveoli, where they slowly hydrolyze into $\text{HCl}$ or $\text{HNO}_3$ over 4 to 24 hours.	Deceptive 4-to-24-Hour Latent Phase: Mild cough or chest tickle at first; victim goes home feeling fine, then wakes up in the middle of the night 6 to 24 hours later drowning in massive delayed pulmonary edema (ARDS).	Mandatory 24-hour hospital observation after any confirmed phosgene or silo-gas inhalation (even if completely asymptomatic); strict bed rest; early CPAP / PEEP ventilation.
Simple Asphyxiants (Carbon Dioxide [$CO_2$], Nitrogen [$N_2$], Methane [$CH_4$], Argon, Helium, Propane)	Dry ice sublimating in closed cars/walk-in coolers; wine/beer fermentation vats ($CO_2$); liquid nitrogen dewars; ship rusting ballast tanks (oxygen depletion); natural gas leaks.	Completely odorless, colorless, and non-irritating ($CO_2$ and Argon are heavier than air; Nitrogen and Methane are lighter).	Displaces atmospheric oxygen ($O_2$) below the normal 20.9% down to `< 10%, 12%` without causing airway burns.	Rapid breathing, dizziness, tunnel vision, confusion, euphoria, and sudden loss of consciousness without warning cough when $FiO_2$ drops below 10%; cardiac arrest within minutes.	SCBA rescue to fresh 21% outdoor air + 100% Oxygen and CPR if apneic. Recovery is rapid and complete if rescued before hypoxic brain injury.

Deep dive 1: Hydrogen Sulfide ($H_2S$): The "Knockdown" Gas and the Blackened Coin Clue¶

Hydrogen sulfide ($H_2S$) is the #1 chemical cause of sudden occupational death in sewer maintenance, septic pumping, oil and gas extraction ("sour gas"), and livestock farming.

Why agitating a farm manure pit or opening a sewer trap triggers an instant disaster¶

As anaerobic bacteria break down sulfur-containing proteins in human sewage or liquid pig/dairy manure stored beneath slatted barn floors, massive quantities of dissolved hydrogen sulfide ($H_2S$), methane, ammonia, and carbon dioxide become trapped under a crust in the liquid slurry.

The Slurry Agitation Spike: The moment a farmer turns on a pump to agitate a liquid manure pit prior to pumping, or a plumber breaks open a blocked sewer trap, trapped $H_2S$ gas bubbles violently out of solution: driving the room or pit air concentration from a safe 5 ppm to over 1,000 ppm in less than 60 seconds.
Concentration-Dependent Effects of $H_2S$:
0.01 to 0.3 ppm: Odor threshold: distinct rotten egg smell (completely harmless at this trace level).
10 to 50 ppm: "Gas Eye" (Keratoconjunctivitis): stinging, tearing eyes, gritty "sand in the eyes" pain, photophobia, and seeing rainbow halos around lights, plus sore throat and cough.
100 to 150 ppm (IDLH: Immediately Dangerous to Life or Health): Complete paralysis of the olfactory nerve within 2 to 15 minutes. You can no longer smell rotten eggs at all.
500 to 700 ppm: Staggering collapse, coma, and respiratory paralysis within 1 to 5 minutes.
700 to 1,000+ ppm ("Slaughterhouse Sledgehammer"): Instantaneous knockdown on the VERY FIRST BREATH. The victim collapses to the floor as if struck in the head with a sledgehammer, stops breathing immediately due to brainstem respiratory center paralysis, and suffers hypoxic cardiac arrest within minutes.
The "Blackened Coins and Silver Jewelry" Clue for First Responders: Hydrogen sulfide reacts instantly on contact with copper, brass, and silver metals to form black copper sulfide or silver sulfide. If paramedics arrive at an unexplained collapse in a basement, bathroom, hotel room, or industrial site and notice that quarters, dimes, pennies, brass belt buckles, or silver rings/necklaces on the victim have turned dull charcoal black, suspect Hydrogen Sulfide ($H_2S$) gas immediately and evacuate the building until fire department gas meters clear the air.

Deep dive 2: Cyanide in House Fires and the Hydroxocobalamin (Cyanokit) Revolution¶

Most people know that Carbon Monoxide ($CO$) is a deadly gas in structural house and building fires (see our carbon monoxide and smoke inhalation guide). What many people do not realize is that modern house fires are equally a Hydrogen Cyanide ($HCN$) emergency.

Why modern synthetic home furnishings generate lethal Cyanide smoke¶

Fifty years ago, furniture, carpets, and curtains were made of natural cotton and wood, which primarily burned into carbon monoxide. Today, homes and offices are filled with nitrogen-containing synthetic polymers: polyurethane foam mattress and couch cushions, nylon carpets, acrylic blankets, melamine laminates, PVC wiring, plus natural wool and silk. When these synthetic materials burn or smolder in a low-oxygen room fire, they release dense clouds of Hydrogen Cyanide ($HCN$) gas.

The Twin Murderers of Smoke Inhalation: Carbon monoxide ($CO$) and Hydrogen Cyanide ($HCN$) act synergistically to kill a smoke inhalation victim. Because $HCN$ has a 35-times shorter blood half-life and causes immediate coma, apnea, and hypotension within seconds, anyone pulled unconscious or in cardiac arrest from an enclosed structural fire with soot around their mouth or nose must be treated empirically for both Carbon Monoxide AND Cyanide poisoning on the spot.

Why Hydroxocobalamin (Cyanokit) is the gold-standard antidote in smoke inhalation¶

Historically, hospitals treated cyanide poisoning with the old 3-step Taylor / Lilly Cyanide Antidote Kit (Amyl Nitrite inhaled ampules + Intravenous Sodium Nitrite + Intravenous Sodium Thiosulfate). How did nitrites work? Sodium nitrite intentionally oxidized 10 percent to 20 percent of the patient's normal oxygen-carrying hemoglobin into Methemoglobin ($Fe^{3+}$), which then pulled cyanide off the mitochondria to form cyanmethemoglobin.

Why you must NEVER give Nitrites to a house-fire smoke inhalation victim: In a house fire victim whose red blood cells are already 20 percent to 40 percent poisoned by Carbon Monoxide (carboxyhemoglobin), injecting Sodium Nitrite converts another 20 percent of their remaining hemoglobin into non-oxygen-carrying Methemoglobin: stripping away the last of their oxygen-carrying capacity and causing fatal asphyxiation.
How Hydroxocobalamin (Cyanokit) saves smoke inhalation victims safely:
Hydroxocobalamin is the natural precursor of Vitamin B12 ($B_{12a}$). Each hydroxocobalamin molecule contains a central cobalt ion that binds directly to a cyanide ion with greater affinity than cytochrome c oxidase, forming Cyanocobalamin (ordinary, non-toxic Vitamin B12), which is excreted harmlessly out in the urine: without creating any methemoglobin and without lowering blood pressure (in fact, hydroxocobalamin scavenges nitric oxide and rapidly raises blood pressure in patients in shock).
Adult Dose: 5 grams intravenously over 15 minutes (can be repeated once for a total of 10 grams in cardiac arrest or refractory shock; pediatric dose is 70 mg/kg IV, max 5 g), often paired via a separate IV line with Sodium Thiosulfate (12.5 grams IV), which donates a sulfur atom via the liver enzyme rhodanese to convert cyanide into harmless thiocyanate.
Harmless Side Effect to Expect: Because hydroxocobalamin is an intense dark burgundy-red pigment, it turns the patient's skin, tears, sweat, and urine bright wine-red (chromaturia) for 1 to 2 weeks after treatment. This red discoloration is completely harmless and shows the antidote is circulating.

Deep dive 3: Household Cleaner Mixing Emergencies (Bleach + Ammonia or Acid)¶

Thousands of emergency department visits occur every year when someone tries to "super-clean" a dirty toilet bowl, shower stall, cat litter box, or clogged drain by pouring two different household cleaners together in a small, unventilated bathroom:

Sodium Hypochlorite Bleach + Ammonia (or Urine in a toilet/cat box) $\rightarrow$ Chloramine Gas ($NH_2Cl$ and $NCl_3$): Causes immediate burning watery eyes, violent coughing, throat irritation, chest tightness, and wheezing.
Sodium Hypochlorite Bleach + Acid (Toilet Bowl Cleaner, Muriatic Acid, Vinegar, Lime/Rust Remover, or Drain Opener) $\rightarrow$ Pure Chlorine Gas ($Cl_2$): Releases a heavy, greenish-yellow cloud of corrosive chlorine gas that reacts with airway moisture to form hydrochloric acid and hypochlorous acid right inside the lungs.
What to do immediately if you mixed cleaners indoors:
Hold your breath and walk out of the bathroom/room immediately: do not stay inside holding your breath for 2 minutes trying to scrub or flush the toilet.
Open exterior windows and doors to cross-ventilate the house and move everyone (and pets) outside into fresh outdoor air.
If your coughing stops within 5 to 10 minutes in fresh air and you have no shortness of breath, wheezing, chest pain, or voice hoarseness, call Poison Control (1-800-222-1222 in the US) for home monitoring guidance.
Go to the Emergency Department or call 911 / 112 / 999 immediately if coughing is persistent, if you hear whistling/wheezing in your chest, if you have a history of asthme or COPD, or if you feel short of breath. In the emergency room, inhaling nebulized albuterol paired with nebulized 2% to 3.75% sodium bicarbonate rapidly neutralizes hydrochloric acid in the bronchial tree and relieves chest pain and wheezing.

Deep dive 4: The "4-to-24-Hour Delayed Pulmonary Edema" Trap (Phosgene & Silo Gas)¶

Why do welders, mechanics, and farmers sometimes walk away from a brief gas exposure feeling completely fine at 2:00 PM, only to die of acute respiratory failure at 2:00 AM that night?

The Water-Solubility Law of Irritant Gases:
Highly water-soluble gases (like Ammonia and Sulfur Dioxide) dissolve the instant they touch the wet lining of your eyes, nose, and throat. Because they burn your nose and throat immediately within 1 second, they trigger an instant alarm reflex that forces you to run away before much gas reaches your deep lungs.
Poorly water-soluble gases: specifically Phosgene ($COCl_2$) (formed whenever a mechanic welds, brazes, or uses a blowtorch on metal parts that were just sprayed with chlorinated brake cleaner containing tetrachloroethylene or methylene chloride) and Nitrogen Dioxide ($NO_2$) (formed in the first 14 days after filling a farm silo with fresh corn or alfalfa silage): do NOT dissolve in the wet nose or throat.
Silent Alveolar Destruction: Because phosgene and nitrogen dioxide do not irritate the nose or throat strongly at low-to-moderate levels, the worker breathes them deep into the microscopic alveoli at the bottom of the lungs without coughing much. Over the next 4 to 24 hours, the gas slowly hydrolyzes on the alveolar-capillary membrane into hydrochloric or nitric acid, stripping away surfactant and causing the lungs to suddenly flood with protein-rich fluid (delayed non-cardiogenic pulmonary edema / ARDS). Anyone who inhales phosgene fumes (welding over brake cleaner) or brownish-yellow silo gas must remain under hospital observation for a minimum of 12 to 24 hours with zero physical exertion, even if they feel 100 percent asymptomatic at first.

Questions fréquemment posées¶

If someone collapses at the bottom of a manhole, septic tank, or farm manure pit, why can't I just take a deep breath, hold my breath for 30 seconds, and climb down to hook a rope on them?

Three physical realities make "holding your breath" a death sentence in confined-space rescues: First, lifting a dead-weight 80-kilogram (175-pound) unconscious adult up a vertical ladder is physically impossible while holding your breath; within 15 seconds of heavy exertion in a low-oxygen or toxic pit, your brain's involuntary diaphragm reflex forces you to gasp. Second, taking just ONE single breath of concentrated Hydrogen Sulfide (> 700 to 1,000 ppm) or 0% oxygen nitrogen atmosphere causes instantaneous loss of consciousness ("knockdown") in 2 to 3 seconds. Third, toxic gases like hydrogen sulfide and hydrogen cyanide also absorb through your wet eyes and skin. Wait for firefighters wearing positive-pressure SCBA tanks and a mechanical tripod winch.

I accidentally mixed bleach and vinegar (or bleach and ammonia) while cleaning the bathroom, coughed a couple of times as I ran outside, and now 20 minutes later in fresh air I feel completely fine. Do I need to go to the ER?

Unlike phosgene or nitrogen dioxide (which have a 24-hour delayed onset), chlorine and chloramine gas from household bleach mixtures have intermediate-to-high water solubility, meaning they cause immediate irritation on contact. If you exited to fresh air immediately, your coughing and eye stinging have completely stopped within 15 to 30 minutes, your voice is normal, and your breathing feels 100% clear and effortless at rest, you can call Poison Control (1-800-222-1222 in the US) and usually remain safely at home while airing out the house. However, if you have persistent coughing, chest tightness, wheezing, shortness of breath, or underlying asthma/COPD, go to an emergency department immediately.

Why did the mechanic's shop warn us NEVER to use chlorinated brake-parts cleaner on metal that is about to be welded?

Many heavy-duty automotive brake cleaners and metal degreasers contain chlorinated hydrocarbon solvents (such as tetrachloroethylene / perchloroethylene, trichloroethylene, or methylene chloride). Even if the metal looks dry after spraying, tiny amounts of solvent remain trapped in microscopic pores or seams of the metal. The instant an electric TIG/MIG welding arc or oxyacetylene torch (or ultraviolet light from the welding arc) hits that residual chlorinated solvent, it thermally decomposes into **Phosgene gas ($COCl_2$)**: the exact lethal chemical warfare gas used in World War I. Inhaling even a few breaths of phosgene while welding can cause fatal delayed pulmonary edema 6 to 24 hours later. Always use non-chlorinated brake cleaner on any part that will be heated or welded.

Can a surgical mask, N95 dust respirator, or a wet towel tied over my face protect me from sewer gas, chlorine, ammonia, or carbon monoxide?

No: they provide ZERO protection against toxic gases or oxygen deficiency. Particulate respirators (like N95, KN95, or P100 masks) only filter solid dust particles and liquid droplets; gas molecules (like $H_2S$, $HCN$, $CO$, $Cl_2$, and $NH_3$) are thousands of times smaller than the filter pores and pass straight through an N95 mask as if it were a screen door. In addition, in a confined space where oxygen has been displaced below 19.5%, even an industrial chemical cartridge gas mask cannot supply oxygen: only a positive-pressure Self-Contained Breathing Apparatus (SCBA) with its own compressed air tank or a supplied-air airline respirator can keep you alive.

This guide is for informational purposes and does not replace professional medical evaluation or hands-on training. Because toxic gas rescues frequently require immediate cardiopulmonary resuscitation once the victim reaches fresh air, we strongly recommend taking an accredited first aid and CPR course through the International Federation of Red Cross and Red Crescent Societies (IFRC), your national Red Cross society, St John Ambulance, or a certified local training provider.

Sources vérifiées¶

National Institute for Occupational Safety and Health (NIOSH, United States) & Centers for Disease Control and Prevention (CDC): NIOSH Pocket Guide to Chemical Hazards (Hydrogen Sulfide, Hydrogen Cyanide, Chlorine, Ammonia, and Phosgene) and Preventing Deaths of Farm Workers in Manure Pits / Confined Spaces.
Agency for Toxic Substances and Disease Registry (ATSDR, United States): Medical Management Guidelines for Hydrogen Sulfide ($H_2S$), Hydrogen Cyanide ($HCN$), Chlorine, Ammonia, and Phosgene.
World Health Organization (WHO): International Programme on Chemical Safety (IPCS): Poisons Information Monographs on Cyanides, Hydrogen Sulfide, and Irritant Gases.
UK Health Security Agency (UKHSA, United Kingdom): Chemical Hazards Compendium: Incident Management and Toxicology of Hydrogen Cyanide, Hydrogen Sulfide, Chlorine, and Phosgene.
Occupational Safety and Health Administration (OSHA, United States): Permit-Required Confined Spaces Standard (29 CFR 1910.146) and Hydrogen Sulfide Fact Sheet.

Sauvetage par inhalation de sulfure d'hydrogène (gaz d'égout), de cyanure et de gaz toxiques¶

Fais ça maintenant¶

Emergency field rescue and toxic gas triage flowchart¶

Pathophysiology of the "Cellular Asphyxiants": Cyanide (\(HCN\)) and Hydrogen Sulfide (\(H_2S\))¶

How Cytochrome c Oxidase Inhibition stops cellular respiration¶

Master diagnostic comparison of Industrial, Agricultural, and Household Toxic Gases¶

Deep dive 1: Hydrogen Sulfide (\(H_2S\)): The "Knockdown" Gas and the Blackened Coin Clue¶

Why agitating a farm manure pit or opening a sewer trap triggers an instant disaster¶

Deep dive 2: Cyanide in House Fires and the Hydroxocobalamin (Cyanokit) Revolution¶

Why modern synthetic home furnishings generate lethal Cyanide smoke¶

Why Hydroxocobalamin (Cyanokit) is the gold-standard antidote in smoke inhalation¶

Deep dive 3: Household Cleaner Mixing Emergencies (Bleach + Ammonia or Acid)¶

Deep dive 4: The "4-to-24-Hour Delayed Pulmonary Edema" Trap (Phosgene & Silo Gas)¶

Questions fréquemment posées¶

Sources vérifiées¶

Guides associés¶

Gas & Chemical Formula	Common Sources & High-Risk Scenes	Odor, Density & Physical Clues	Toxicological Mechanism	Classic Clinical Presentation	Definitive Antidote & Hospital Management
Hydrogen Cyanide (\(HCN\)) & Cyanide Salts	Structural house/building fire smoke (burning wool, silk, polyurethane foam, nylon, plastics, melamine), gold/silver mining, electroplating, jewelry cleaning, acetonitrile nail remover, sodium nitroprusside, apricot/cassava pits.	Bitter almonds odor (detectable by only 40%, 60% of people genetically); lighter than air (\(HCN\) gas). Soot around mouth/nose in fire victims.	Binds \(Fe^{3+}\) in mitochondrial Cytochrome c Oxidase \(\rightarrow\) halts cellular oxygen use \(\rightarrow\) fulminant anaerobic lactic acidosis.	"Knockdown" collapse within seconds at high gas levels; confusion, gasping tachypnea followed by apnea, seizures, coma, cardiovascular collapse/bradycardia, and Serum Lactate `>= 8 to 10 mmol/L`.	1. 100% High-Flow Oxygen. 2. IV Hydroxocobalamin (Cyanokit 5 g IV over 15 min) (binds cyanide to form harmless Vitamin B12 excreted in urine). 3. IV Sodium Thiosulfate (12.5 g IV).
Hydrogen Sulfide (\(H_2S\) / "Sewer Gas" / "Sour Gas")	Sewers, septic tanks, cesspools, underground utility vaults, agricultural liquid manure pits, petroleum/natural gas ("sour crude") refineries, paper mills, tanneries, hot springs/volcanic vents, mixing toilet acid with sulfur products ("detergent suicide").	Rotten eggs odor at low levels (`< 30 ppm`), suivie d'une paralysie complète du nerf olfactif au-dessus de 100 à 150 ppm ; plus lourd que l'air (coule dans les fosses) ; noircit les pièces de cuivre et les bijoux en argent dans les poches de la victime.	Binds \(Fe^{3+}\) in mitochondrial Cytochrome c Oxidase (identical to cyanide) + direct corrosive mucosal injury to eyes and alveoli.	Low levels (10 to 100 ppm): "Gas Eye" (painful keratoconjunctivitis, gritty eyes, halos around lights) + cough. High levels (`> 500 to 1,000 ppm`): Single-breath "Slaughterhouse Sledgehammer Knockdown" (instant coma, seizures, apnea, and cardiac arrest).	1. Strict SCBA Confined-Space Rescue. 2. Strip clothing & give 100% High-Flow Oxygen / Intubation (\(H_2S\) dissociates faster than cyanide with \(O_2\)). 3. IV Sodium Nitrite (300 mg) or Hydroxocobalamin if given immediately (consult Poison Control).
Chlorine (\(Cl_2\)) & Chloramine (\(NH_2Cl\)) Gas	Mixing household sodium hypochlorite bleach with Ammonia (\(\rightarrow\) Chloramine gas) or with Acid toilet bowl cleaner / vinegar / muriatic acid (\(\rightarrow\) pure Chlorine gas); swimming pool chemical rooms; water treatment plant leaks.	Pungent, suffocating bleach/swimming-pool odor; greenish-yellow haze at high concentration; Chlorine is 2.5x heavier than air.	Intermediate water solubility: Dissolves in airway moisture to form Hydrochloric Acid (\(\text{HCl}\)) and Hypochlorous Acid (\(\text{HOCl}\)), burning from the throat down to the alveoli.	Immediate violent coughing, choking, burning eyes/throat, retrosternal chest pain, laryngospasm (stridor), severe bronchospasm (wheezing), and acute non-cardiogenic pulmonary edema.	Evacuate to fresh air; flush eyes 15 min; 100% Humidified Oxygen; Nebulized Albuterol for wheezing + Nebulized 2% to 3.75% Sodium Bicarbonate (4 mL) to neutralize airway acid.
Anhydrous Ammonia (\(NH_3\))	Agricultural fertilizer tanks, industrial cold-storage/ice-rink refrigeration plants, methamphetamine labs, industrial cleaners.	Fiercely pungent, suffocating ammonia odor; lighter than air (unless cold pressurized liquid aerosol cloud, which hugs the ground).	High water solubility: Reacts instantly with moisture on the eyes, mouth, and upper airway (larynx/trachea) to form caustic Ammonium Hydroxide (\(\text{NH}_4\text{OH}\)) alkali burns.	Immediate upper airway catastrophe: Blinding corneal liquefaction burns, massive swelling of the lips/tongue/epiglottis, hoarse voice, high-pitched inspiratory stridor, and rapid upper-airway suffocation.	Flush eyes and skin with copious water for at least 15 to 30 minutes; early endotracheal intubation (before throat swells shut completely); humidified \(O_2\) and bronchodilators.
Phosgene (\(COCl_2\)) & Nitrogen Dioxide (\(NO_2\) / "Silo Filler's Disease")	Phosgene: Welding, brazing, or heat stripping metal cleaned with chlorinated brake cleaner (tetrachloroethylene / trichloroethylene); burning Freon/refrigerants. Nitrogen Dioxide (\(NO_2\)): Freshly filled farm grain/corn silos (first 2 weeks); diesel exhaust; nitric acid spills.	Phosgene: Smells pleasantly like freshly mown hay or cut green corn. \(NO_2\): Reddish-brown heavy gas at bottom of silos with sharp bleach-like odor.	Low water solubility: Because they do NOT dissolve in the wet nose or throat, they cause minimal early coughing, allowing the victim to inhale them deep into the alveoli, where they slowly hydrolyze into \(\text{HCl}\) or \(\text{HNO}_3\) over 4 to 24 hours.	Deceptive 4-to-24-Hour Latent Phase: Mild cough or chest tickle at first; victim goes home feeling fine, then wakes up in the middle of the night 6 to 24 hours later drowning in massive delayed pulmonary edema (ARDS).	Mandatory 24-hour hospital observation after any confirmed phosgene or silo-gas inhalation (even if completely asymptomatic); strict bed rest; early CPAP / PEEP ventilation.
Simple Asphyxiants (Carbon Dioxide [\(CO_2\)], Nitrogen [\(N_2\)], Methane [\(CH_4\)], Argon, Helium, Propane)	Dry ice sublimating in closed cars/walk-in coolers; wine/beer fermentation vats (\(CO_2\)); liquid nitrogen dewars; ship rusting ballast tanks (oxygen depletion); natural gas leaks.	Completely odorless, colorless, and non-irritating (\(CO_2\) and Argon are heavier than air; Nitrogen and Methane are lighter).	Displaces atmospheric oxygen (\(O_2\)) below the normal 20.9% down to `< 10%, 12%` without causing airway burns.	Rapid breathing, dizziness, tunnel vision, confusion, euphoria, and sudden loss of consciousness without warning cough when \(FiO_2\) drops below 10%; cardiac arrest within minutes.	SCBA rescue to fresh 21% outdoor air + 100% Oxygen and CPR if apneic. Recovery is rapid and complete if rescued before hypoxic brain injury.