How the Experts Identify Chemical Weapons and Prove an Attack

After the Syrian government was accused of ­gassing its own people—which it denied doing—­experts went in to find the truth.

Getty ImagesGeorge Frey

This April, after a suspected chemical weapons attack in Douma, Syria, killed dozens of people and sickened hundreds more, an international monitoring group called the Organisation for the Prohibition of Chemical Weapons sent a team to investigate. In May the OPCW released its results: suspected chlorine gas. Jerry Smith, who served as senior inspection team leader at OPCW from 2011 to 2012 and the head of contingency operations from 2013 to 2014, explains the process.

Where They Collect Samples

In the first visit to Douma—two weeks after the attack—inspectors gathered more than 100 samples. Witness or victim interviews are best. They help you narrow down the search area. You can also take blood or urine samples from the victims. (If there are fatalities, you take slices of liver from the bodies.) Depending on the chemical agent used, there will be markers left in the body for around two weeks. Outside the body, chemical agents such as VX can hang around for up to three weeks.

The bottom of the crater left by the suspected device is always a good place to start looking. The action of the agent being distributed forces some of the payload into the ground. If you don’t know where the crater is, you can look at absorbent materials—a mattress, clothing, blankets, piles of dirt or dust, or even paper. Sometimes investigators do a quick field test to determine if samples are worth testing in a lab. They’ll put found clothing or paper in a bag and leave it in the sun, which causes some of the liquid to evaporate. You can then stick something called a Draeger tube into the bag. It’s a small glass vial about the size of a pencil. You snap off each end and attach it to a hand pump. Use the hand pump to suck in a sample, and then feed the sample through a sensor. If you get a hit, you can be confident you have material to take to a lab.

You can also check channels where liquid might pool. The threadings in ammunition casings, for example. With chlorine, most of the gas will dissipate in the wind, but it reacts with certain metals to form salts, and those salts might be present in the soil.

What Happens to the Samples

Assad Regime's alleged chemical gas attack in Eastern Ghouta
Getty ImagesAnadolu Agency

One sample takes three people and ten to 15 minutes to collect. One person takes the sample, one receives it, and one records it. Each sample is taken using a forensically secure sample kit. It’s completely sterile and contains a cylindrical scoop and two to three sizes of sealed containers and a secondary and sometimes even tertiary plastic pack to protect it. If you happen to find actual “neat” (unadulterated) agent, it goes into toxic-transport containers, which are made of material a bit like an airplane’s black box. These are put in wooden boxes with cork lining, and those are put in stainless steel with a bolt-down lid. Inside is powdered activated charcoal to absorb any potential leakage. They’re wrapped two to three times in a protective coating. Biomedical samples such as blood or urine are typically stored in glass with nonreactive caps and seals and then packed in two to three layers for protection.

Once a sample is taken, it’s given a unique number. Investigators document when it was taken, who took it and where, and the weather conditions. Planes fly the samples to OPCW’s main lab in Rijswijk, Netherlands. OPCW keeps part of the sample for its records, and it might keep part for the country the samples were taken from. Other samples are sent off to a network of labs, labeled only by a number. Sometimes the labs receive actual samples and sometimes they get blanks, or spoofs with some other chemical. Everything has to be controlled. Liquid samples can be tested with detector paper, which is similar to a large piece of litmus paper. It changes colors if an agent is present. The other major liquid-sample technology is Fourier-transform infrared spectroscopy. When a sample is placed in the machine, infrared light shines through it. The molecules inside the liquid will bend or reflect the light in certain ways, which the machine compares to its library of standard compounds.

Gas samples are placed in a detector called an AP4C, which uses flame spectrophotometry (see below). Another detector, called the Cam, uses ion-mobility spectrometry. The ions from different agents move across a screen, and their travel time is an indicator of what elements are present.

How It Works: The AP4C Detector


Proengin’s AP4C detector analyzes gas and vapor samples using flame spectrophotometry. After a sample is sucked in through the intake port, it passes over a small hydrogen flame. The sample burns in the flame, producing a light wave, the color of which is determined by the elements present, such as phosphorus. That spectrum passes through a focus lens and onto a sensor. The results are run through a processor (6), which analyzes the sample for the presence of four basic elements that are common in chemical weapons: phosphorus, hydrogen-nitrogen-oxygen bonds, arsenic, and sulfur. The AP4C has no onboard library. It does not identify the possible agent. It simply detects the presence of one. The waste is expelled through the exhaust (7). The entire process requires very little sampled product and takes under two seconds to complete.

What the Inspectors Wear

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Impermeable rubber suits are more protective than the thin, charcoal-lined permeable suits, but the heat burden is enormous. The higher the threat—if it’s unknown or there’s massive liquid and vapor contamination—you go with fully encapsulated suits and breathing apparatuses. Otherwise you can use filtering systems, such as gas masks. One tool that everyone carries is a personal atropine or oxime pen—a nerve agent treatment. It’s carried in the same location on the body. That way, when you need to treat someone who might be incapacitated by a chemical agent, you immediately know where to find his pen.

This appears in the September 2018 issue.

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