There is a very good reason why chemical weapons are banned besides the fact that they kill people. In fact, they kill a lot of people. It’s the way people die from chemical weapons. In many cases, you are in extreme pain for quite a while before death comes. It’s a most horrible way to die.
There are five categories of chemical weapons, “nerve, choking, blister, blood, and riot,” Reuters notes. Assad likely used Sarin gas, which is a nerve agent that “causes seizures, loss of body control; paralyses muscles, including heart and diaphragm.” A graphic from Reuters depicts how various kinds of deadly chemical agents effect the human body:
The April 2016 use of the weapons is likely Assad’s first use of a nerve agent since 2013, when Sarin killed hundreds of civilians in Damascus suburbs. Assad however has regularly used chlorine in the Syrian civil war which is a choking agent. Chlorine causes “air sacs in the lungs, to secrete fluid, essentially drowning those affected.”
The first widespread use of chemical weapons dates to World War I when the Germans deployed chlorine gas. Both sides in the war quickly adopted the tactic, and within years tear gas, mustard gas, and chlorine gas were used with impunity. While gas casualties were only a small fraction of casualties in the war, doctors noted that troops were far more afraid of chemical weapons than conventional attacks.