Munitions

Chlorine gas cylinders

Also known as
  • Douma chlorine cylinders
  • chlorine-filled cylinders
  • yellow chlorine cylinders
  • industrial chlorine cylinders
  • chlorine barrel bombs

Chlorine gas cylinders are industrial pressure vessels that become improvised chemical munitions when adapted or delivered to release toxic chlorine intentionally. In the April 2018 U.S., UK, and French strikes in the 2011 Syrian Civil War archive, the relevant use is the Douma attack: OPCW investigators found that Syrian Arab Air Force helicopters dropped two yellow chlorine-filled cylinders on residential buildings, providing the chemical-weapons trigger cited by the United States, United Kingdom, and France for the 14 April 2018 missile strikes.

Chlorine gas cylinders, Improvised chlorine chemical munition, Munitions
Image source: Wikimedia Commons Chlorine in Bottle Image

Role in Conflicts

Improvised Munition Evidence

The Douma evidence treats the cylinders as industrial pressure vessels converted by use into chemical munitions. OPCW reporting separates the munition body, toxic fill, delivery platform, and release effects, which is why this record covers the cylinder payload rather than the Mi-8/17 helicopter that carried it.

Munition body

Two yellow industrial gas cylinders were documented at residential Locations 2 and 4 in Douma.

Sources: Third Report by the OPCW Investigation and Identification Team, Douma; OPCW Douma FFM Final Report PDF.

Toxic fill

The FFM found reasonable grounds that the toxic chemical contained reactive chlorine and was likely molecular chlorine.

Source: OPCW Douma FFM Final Report PDF.

Delivery platform

The IIT attributed the drops to at least one Syrian Arab Air Force Mi-8/17 helicopter operating from Dumayr airbase.

Source: Third Report by the OPCW Investigation and Identification Team, Douma.

Profile / Specs

Profile

Origin
Syria, using industrial chlorine cylinders modified as improvised chemical munitions
Built by
Unknown
Built in
UnknownSyria
Type
Improvised chlorine chemical munition
Service note
Documented in the April 2018 Douma chemical attack and the subsequent strike-crisis context
Designer
Not publicly identified
Designed
Industrial cylinder design adapted as an improvised munition before April 2018
Unit cost
Not publicly reported
Produced
Industrial production; modified weapon configuration not publicly reported
Number built
Two yellow chlorine cylinders documented by OPCW for the Douma incident

Specifications

Chemical agent
Chlorine gas (Cl2), a toxic industrial chemical and choking agent
Container
Pressurized industrial gas cylinder, documented by OPCW as two yellow cylinders in the Douma incident
Delivery method
Dropped from at least one Syrian Arab Air Force Mi-8/17 helicopter, according to OPCW IIT findings
Documented effects
At Location 2 in Douma, OPCW reported rapid high-concentration chlorine release inside a residential building, killing 43 named people and affecting dozens more
Hazard characteristics
Chlorine is heavier than air and can collect in enclosed or low-lying spaces; NIOSH lists a 10 ppm immediately dangerous to life or health value
Variants

The public evidence describes an improvised munition form rather than a standardized model family.

VariantConfigurationDesignation notes
Yellow chlorine-filled industrial cylinderImprovised air-delivered chemical munition

OPCW reports describe two yellow industrial cylinders found at Douma, one on a rooftop at Location 2 and one in a bedroom at Location 4, with the IIT attributing their delivery to Syrian Arab Air Force Mi-8/17 helicopters.

Sources: Third Report by the OPCW Investigation and Identification Team, Douma, OPCW Douma FFM Final Report PDF

Carrier Helicopters
CarrierCarrier typeCarriage evidence
Mi-8/Mi-17, Medium twin-turbine utility transport helicopter, Aircraft & UAVsMi-8/Mi-17Medium twin-turbine utility transport helicopter

OPCW concluded that at least one Syrian Arab Air Force Mi-8/17 helicopter operating in the Douma attack dropped two yellow chlorine cylinders on 7 April 2018.

Sources: Third Report by the OPCW Investigation and Identification Team, Douma

Timeline

Chlorine gas cylinders Key Events

  1. Two cylinders dropped in Douma

    The OPCW IIT later concluded that at least one Syrian Arab Air Force Mi-8/17 helicopter from Dumayr airbase dropped two yellow chlorine cylinders that hit residential buildings in Douma.

    Sources: Third Report by the OPCW Investigation and Identification Team, Douma

  2. Coalition strikes follow Douma attack

    The United States, United Kingdom, and France conducted missile strikes against Syrian government chemical-weapons-related targets after citing the Douma chemical attack.

    Sources: OPCW IIT Douma Report Release

  3. OPCW FFM reports reactive chlorine finding

    The OPCW Fact-Finding Mission reported reasonable grounds that a toxic chemical was used as a weapon in Douma and that the toxic chemical contained reactive chlorine, likely molecular chlorine.

    Sources: OPCW Douma FFM Final Report PDF

  4. OPCW IIT attributes cylinder attack

    The OPCW Investigation and Identification Team attributed the Douma chlorine-cylinder attack to the Syrian Arab Air Force and described the two-cylinder delivery sequence in detail.

    Sources: OPCW IIT Douma Report Release, Third Report by the OPCW Investigation and Identification Team, Douma

Media

Chlorine gas cylinders Images

Chlorine gas cylinders, Improvised chlorine chemical munition, Munitions - view 1
Source: Wikimedia Commons Compressed Gas Bottles Image
Chlorine gas cylinders, Improvised chlorine chemical munition, Munitions - view 2
Source: Wikimedia Commons Chlorine Liquid and Gas Image
Related Weapon Systems
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SCALP-EG, Air-launched cruise missile, MunitionsMunitionsSCALP-EGAir-launched cruise missileSCALP-EG is the French-service member of the Storm Shadow/SCALP air-launched cruise-missile family, an MBDA deep-strike weapon built for pre-planned attacks on high-value fixed targets such as hardened facilities and key infrastructure. French aircraft used SCALP-EG in Libya, Iraq and the 2018 Syria strikes, Ukrainian Su-24 aircraft later carried it as a Western long-range precision-strike option, Indian Rafales were reported to have used SCALP during Operation Sindoor in the 2025 India-Pakistan Conflict, and the UK-France 2025 defence declaration tied new SCALP and Storm Shadow acquisition to production-line upgrades.
MdCN / SCALP Naval, Ship- and submarine-launched land-attack cruise missile, ArtilleryArtilleryMdCN / SCALP NavalShip- and submarine-launched land-attack cruise missileMdCN, also called SCALP Naval or NCM, is MBDA's French naval cruise missile for precision land attack from FREMM frigates and Barracuda/Suffren-class submarines. MBDA describes the weapon as a very-long-range, metric-accuracy deep-strike missile launched either from A70 SYLVER vertical cells or 21-inch submarine torpedo tubes, and French forces used it operationally during the April 2018 U.S., UK, and French strikes in the 2011 Syrian Civil War.

Sources

OPCW IIT Douma Report ReleasePublisher: Organisation for the Prohibition of Chemical Weapons | Note: Supports April 2018 U.S., UK, and French strikes in the 2011 Syrian Civil War context: chlorine gas cylinders were used by the Syrian Arab Air Force in the 7 April 2018 Douma chemical attack that triggered the later coalition missile strikes. | Accessed: 2026-07-04Third Report by the OPCW Investigation and Identification Team, DoumaPublisher: Organisation for the Prohibition of Chemical Weapons | Note: Supports specifications and April 2018 U.S., UK, and French strikes in the 2011 Syrian Civil War context: two yellow chlorine cylinders were used by Syrian Arab Air Force helicopters in Douma, including delivery method, cylinder behavior, and chlorine release effects. | Accessed: 2026-07-04OPCW Douma FFM Final Report PDFPublisher: Organisation for the Prohibition of Chemical Weapons | Note: Supports Douma background and specifications: the FFM described the two yellow industrial cylinders, reported reasonable grounds that a toxic chemical was used as a weapon, and assessed the chemical as reactive chlorine likely involving molecular chlorine. | Accessed: 2026-07-04What is a Chemical Weapon?Publisher: Organisation for the Prohibition of Chemical Weapons | Note: Supports background on how toxic chemicals and delivery devices fall under the chemical-weapon definition when used for prohibited purposes. | Accessed: 2026-07-04Chlorine IDLHPublisher: National Institute for Occupational Safety and Health | Note: Supports chlorine hazard specifications, including immediately dangerous to life or health exposure context. | Accessed: 2026-07-04Chlorine Medical Management GuidelinesPublisher: Agency for Toxic Substances and Disease Registry | Note: Supports chlorine physical and hazard background, including heavier-than-air behavior in enclosed or low-lying areas. | Accessed: 2026-07-04Industrial Chemicals as Weapons: ChlorinePublisher: Nuclear Threat Initiative | Note: Supports background on industrial chlorine, legitimate uses, toxicity, and historical weaponization in cylinders or improvised releases. | Accessed: 2026-07-04Wikimedia Commons Chlorine in Bottle ImagePublisher: Wikimedia Commons | Note: Supports image provenance for the primary chlorine gas image; the file page identifies W. Oelen as author and CC BY-SA 3.0 licensing. | Accessed: 2026-07-04Wikimedia Commons Compressed Gas Bottles ImagePublisher: Wikimedia Commons | Note: Supports image provenance for the compressed-gas-cylinder gallery image; the file page identifies Ildar Sagdejev as author and free-license terms. | Accessed: 2026-07-04Wikimedia Commons Chlorine Liquid and Gas ImagePublisher: Wikimedia Commons | Note: Supports image provenance for the chlorine liquid-and-gas gallery image; the file page identifies W. Oelen as author and CC BY-SA 3.0 licensing. | Accessed: 2026-07-04