The balloons were filled with burning gas - Yerevan 's State University's Professor.

If there was an explosion, it means there was burning gas in the balloons, Yerevan 's State University's Professor of Chemistry Department Shiraz Margaryan said during the talk with LURER.com, commenting on yesterday's incident in Republican Square of Yerevan.
"Either it was hydrogen or methane, or gas mixture. It also could be local accumulation of gas. Both hydrogen and methane are dangerous and non-permitted - both of them would have the same effect. Hydrogen and helium mixture is not dangerous but it is used in air balloons for weight increase. In this case it would be right to fill these balloons with helium, which is an inert gas," mentioned Sargsyan.
According to the professor, the cause of explosion also became the location of the balloons - there were very close to each other, "This is the same as to fill a big ball with gas, this is explosive," stated Sargsyan.
To note, yesterday during the Republican party's final rally in Yerevan's Republic Square as a result of balloon blast about 150 people got burns of different degrees and were hospitalized.