Now all roads lead to France and heavy is the tread
Of the living; but the dead returning lightly dance.
Edward Thomas, Roads

Sunday, November 21, 2021

The Emergence of Phosgene Gas

The shadow of gas warfare is very long and covers us still. The very agents used in the Great War are still causing death and injury through deployment in conflict areas such as Iraq and Syria. Industrial accidents, train derailments and dumped or buried gas shells are other sources of poison gas hazards. In this age of terrorism. . . frontline resuscitation specialists, may be directly involved in the management of gas casualties or become victims ourselves. Several other lethal gases were used in the Great War, including diphosgene, chloropicrin, hydrogen cyanide, arsenic trichloride, and chlorvinyldichlorarsine (dubbed lewisite—the "dew of death"). However in terms of quantity, the most important gases used were chlorine, phosgene, and mustard gas. For example, Germany produced mustard gas at a rate of 300 tons per month. Chlorine was, eventually, chosen as the first gas for mass use.  It proved, however, to have limitations for the user, and counter-measures became more effective.

A more lethal gas emerges

As defenses against chlorine gas became increasingly effective, a new more lethal gas was being developed: phosgene. This gas is easy to manufacture and can be produced, for example, by mixing carbon monoxide and chlorine gas and exposing the mixture to sunlight. It has the chemical formula COCl2  and is colorless and denser than chlorine, reducing its ability to spread easily. Phosgene can also form unintentionally when chloroform or other chlorinated solvent is degraded by ultraviolet light in the presence of oxygen. Trichloroethylene (trilene) can also breakdown to hydrogen chloride, dichloroacetyline, and phosgene at high temperatures as can occur in sodalime. This reaction was described by Australian pediatric anesthetist Margaret McClelland, OBE, in 1944 and is believed to have caused trigeminal nerve toxicity in some patients.

Effects of phosgene

Although high concentrations of phosgene can be rapidly fatal, lower concentrations are much less irritating to breathe than chlorine, with a not unpleasant odor like freshly mown hay. As a consequence, soldiers tended to inhale more phosgene than a similar concentration of chlorine. Soldiers exposed to low concentrations of phosgene could remain battle-effective initially.

However, over hours, phosgene reacts with lung fluids, resulting in the formation of hydrogen chloride and carbon dioxide. Hydrogen chloride then forms  hydrochloric acid, which damages the alveoli leading to severe pulmonary edema and heart failure.

A graphic description of the effects of phosgene poisoning is provided in the book Death’s Men—Soldiers of the Great War:

shallow breathing and retching, pulse up to 120, an ashen face and the discharge of 4 pints of yellow liquid from the lungs each hour for the 48 of the drowning spasms”.  Of the estimated 91,000 deaths due to gassing in the Great War perhaps 80-85% were due to phosgene, mostly Russians on the Eastern front. The Russian soldiers had little protection against any type of gas.      


116 Russian soldiers were victims of a gas attack on
9 August 1916 at Krevo, Belarus

Treatment of phosgene poisoning

Patients exposed to phosgene gas were treated in a similar way to chlorine poisoning including bed rest and oxygen therapy. Venesection was sometimes used, an amount of 15 ounces was described in one case (about 450 ml).

Delivery of phosgene on the battlefield

Phosgene was often mixed with chlorine gas to help spread the denser phosgene. The Allies referred to this mixture as "white star" after the markings on their gas shells. The Germans painted their chlorine/phosgene shells with a green cross. The first German mixed chlorine/phosgene attack occurred at Wieltje, near Ypres in December 1915, using cylinders.

Chlorine/phosgene mixture gas attacks were used extensively during the battle of the Somme (July–November 1916).

Australian Engineers Releasing Phosgene
(Possible Drill?)

Increased troop protection

By the time phosgene was being used in late 1915, the British were using the "P" or Phenate or Tube helmet. Unlike the Hypo Helmet, the P helmet had two mica eye pieces and a mouth piece with an exhaust valve for exhalation. It was made up of two layers of flannel and was soaked in sodium phenylate and glycerine, which provided increased protection against phosgene and chlorine.

The PH helmet was then issued in January 1916. PH stood for phenate/hexamine and hexamethylene tetramine and this combination offered even more protection against phosgene. To counteract the efficiency of these gas helmets, chlorine and phosgene were often delivered with tear gas. This would cause lacrimation, coughing and choking and tempt the soldier to pull off his gas helmet and subsequently be gassed.

In January 1916 the familiar canister gas-mask was introduced with a face mask, hose, and a canister containing absorbent materials to filter out or destroy toxic  gases. This British version was known as the "Small Box Respirator," and it was carried in a bag on the chest at all times. Materials in the canister included pumice mixed with hexamine to neutralize phosgene and powdered charcoal mixed with potassium carbonate to neutralize chlorine. Activated charcoal was used extensively. It is a highly porous form with greatly increased surface area and increased absorbency.  Wood charcoal was used initially as the absorbent, but charcoal made from seeds, nuts, fruit stones and shells was found to be more effective. The Germans favored a version of the gas mask that dispensed with the hose between the mask and the canister, called snout canisters.

But then a new horror appeared—mustard gas—"the king of battle gases."

A final thought on today's threats

In the era of terrorism that we all live in, poisonous gas is being used to forward the twisted ideology of various groups. For example on 14 March 2016 the Daily Telegraph in Sydney reported that Islamic State militants used chlorine gas and sulfur mustard when attacking the northern Iraq city of Kirkuk.

We must not think of poisonous gas as merely a very dark chapter of a very terrible war but rather an ongoing menace to combatants and civilians alike in a world stricken by conflicts past, present, and future.

From: "Gas: The Greatest Terror of the Great War," A.P. Padley, Westmead Hospital, Westmead, NSW


  1. I have often wondered why those in the chemical industry who developed and produced these gases were not prosecuted as war criminals. Though the Germans started the whole thing and were much more effective at producing these gases, the whole situation was complicated by the fact that the allies followed the Germans in the use of gases, just not as effectively and as extensively. The Germans were also Masters of the delivery of gas via artillery shells. As we see in other areas, the Germans were quite willing to break any rule if they thought they could gain some advantage from it. Submarine sinking of passenger ships, use of slave labor, killing of civilians and use of gas are just a few of the examples.

  2. The story of Fritz Haber is really informative in this context. See the book Master Mind: The Rise and Fall of Fritz Haber, by Daniel Charles.

  3. How did i end up from studying organic chemistry of alkyl halides to seeing how warcrimes are commited