ALEPPO, Syria - Mohammad Zayed, a former student at Homs University, dedicates his days to teaching volunteers how to help fellow Syrians cope with a chemical weapons attack - just in case.
"The regime has sarin, the VX (nerve) agent and mustard gas," chemistry student Zayed, 21, tells his team of volunteers in the northern city of Aleppo.
"If it's a sarin attack, you need to open the windows to ventilate the houses. It's a very lethal gas but it disperses quickly.
"VX is more dangerous. We cannot take off the protective clothing at any time because it penetrates the body not only through our respiratory system but also through the skin and eyes," says Zayed.
Sarin is a paralysing, odourless agent that can kill in minutes and was developed by Nazi scientists in 1938.
Several Western countries and Syrian opposition groups say the regime used it in the rebel-held areas of Eastern Ghouta and Moadamiyet al-Sham in the outskirts of Damascus on August 21.
VX is an even more deadly derivative of sarin, while mustard gas causes suffocation and severe burning of the eyes and respiratory system.
The United States says there are some 45 sites in Syria linked to the regime's chemical arms programme.