Chemical weaponsSyria chlorine attack claims: what this chemical is and how it became a weapon

By Simon Cotton

Published 8 September 2016

New claims that the Syrian government has dropped barrel bombs full of chlorine on a suburb of Aleppo are the latest in a series of allegations of chemical weapon use. Although the Syrian government denies using chemical weapons, a recent UN-led enquiry found it had used chlorine on at least two occasions. The first gas attack using chlorine was launched on 22 April 1915 in the trenches on the Western front, near Ypres. Gas masks were developed to protect against chlorine attacks and other chemical warfare agents were developed. But chlorine remains the simplest chemical weapon and reappeared on the battlefield during the Iraq War and allegedly now in Syria. In the Second World War, both sides of the conflict knew that the other side had weaponized chlorine and refrained from using it. Today in Syria, it sadly appears this may not have been the case.

New claims that the Syrian government has dropped barrel bombs full of chlorine on a suburb of Aleppo are the latest in a series of allegations of chemical weapon use. Although the Syrian government denies using chemical weapons, a recent UN-led enquiry found it had used chlorine on at least two occasions.

Here’s what you need to know about chlorine and its use as a chemical weapon

Greenish-yellow gas
The chemical element chlorine is too reactive to exist on its own in nature, but some of the compounds that contain it are essential to life. We use hydrochloric acid (HCl) in our stomachs to break down food and destroy bacteria, while sodium chloride (NaCl) — the common salt we add to food – is so important that it was once used as a currency.

Pure chlorine was first isolated from hydrochloric acid by Carl Wilhelm Scheele in 1774. Within a few years, its bleaching properties were discovered and in 1810 Humphry Davy announced that it was a chemical element. At room temperature, it is a greenish-yellow gas with a choking smell, which is denser than air.

Dry chlorine gas won’t bleach, but in water it forms hypochlorite, responsible for the bleaching action, and also responsible for its disinfectant action. It was first used to disinfect tap water at the time of a typhoid outbreak in Maidstone in 1897. Since then the process has been generally adopted.

Forty million tons of chlorine is manufactured a year, among other things for use in making many pharmaceuticals. Thousands of organic chlorine compounds occur naturally including vancomycin, which for many years was the antibiotic of last resort and is made in natureby a bacterium in the soil.

Health dangers
But chlorine itself is very reactive with the human body and very toxic. It irritates the eyes and skin and, even at quite low levels, can causes permanent lung damage even if it does not kill you. Breathing high levels of chlorine causes pulmonary oedema — fluid buildup in the lungs.

Accidents with chlorine do happen. In Graniteville, South Carolina, on 6 January 2005, a railroad tanker full of liquefied chlorine gas was punctured killing eight people that day, with another fatality three months later attributed to inhaling the gas. More than 5,000 people were evacuated from its immediate vicinity and some have health problems more than ten years later.