HOW YOUR WORLD WORKS

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

LAST 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 their 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 in it 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. The hand pump is used to suck a sample in, 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 threading 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 could be present in the soil.

WHAT HAPPENS TO THOSE SAMPLES

One sample takes three people and 10 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 or 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 aeroplane’s black box. These are put in wooden boxes with cork lining, and those are put in stainless steel with a bolt-down lid and wrapped a few more times in a protective coating. Inside is powdered activated charcoal to absorb any potential leakage. Biomedical samples such as blood or urine are typically stored in glass with non-reactive caps and seals and 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 of origin. Other samples are sent off to a network of labs, known 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 colours if an agent is present. The other major liquid-sample technology used is Fourier-transform infrared spectroscopy, where a sample is placed in a machine and infrared light is shone 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 makes use of flame spectrophotometry (see below). Another detector, called the CAM, employs ionmobility spectrometry – the ions from different agents move across a screen, and their travel time is an indicator of which elements are present.