The images of the aftermath of the latest reported chemical attacks in Syria are disturbing.
Men and women stripped to the chest, being hosed with water to rid them of chlorine; children and babies with oxygen masks, struggling for breath.
The US State Department says it has recorded six suspected chemical attacks in Syria in the past 30 days, but there are suggestions that number is conservative.
One expert told me he was aware of 10 incidents in the last week alone.
Chlorine isn’t sophisticated – it was first used in the First World War.
It is a weapon of fear, designed to terrorise a population, even if it doesn’t kill in large numbers.
The use of any chemical weapons is a war crime, banned under the Geneva Convention.
If independent monitors were allowed on to the ground to collect evidence, they might be able to ascertain beyond doubt who is to blame and that might one day end up in an international court.
Alas, they are not. Instead the regime prevents access, helped by Russian cover.
When the UN Security Council tries to pass motions condemning the use of chemical weapons, Russia repeatedly vetoes.
After the sarin attacks in Syria in 2013, an international body – the Union of Medical Care and Relief Organisations – set up a CBRN (chemical, biological, radiological and nuclear) taskforce.
Local medics were educated on how to treat casualties and rescue workers were trained to gather evidence in absence of independent experts.
It nevertheless remains hard to get any gathered evidence safely out of Syria.
Slowly, backed by Iran and Russia, Syrian president Bashar al Assad has recaptured territory. His forces now hold major urban centres and large swathes of Syrian land.
But the provinces of Ghouta and Idlib still remain under rebel control and western governments fear a massacre as Assad tries to recapture those last bastions.
In Aleppo, chlorine has reportedly been used to flush rebel soldiers out from underground bunkers.
British chemical weapons experts believe there is now evidence that Syrian troops are putting sarin into grenades.
If this proves to be true, it will be a new development – a “game-changer,” as it was described to me.
The desperate truth about chemical weapons is that they tend to work – they have the desired effect, however horrendous.
If Assad is under pressure to recapture Idlib and Ghouta quickly, he might resort to more chemical weapons usage to finish the job.