The use of tear gas by police against Occupy protesters has been a constant subject of debate since October’s night of violence at Occupy Oakland. Many have begun to ask the question:. Just how dangerous are these “non-lethal” weapons being used?

Egyptian protesters wear masks for protection against tear gas during clashes Wednesday with riot police near Tahrir Square. (MAHMUD HAMS/AFP/GETTY IMAGES)

Tear gas made an appearance in South Korea yesterday, when lawmaker Kim Sun-dong released tear gas in what may be a first for a legislative session, in an attempt to prevent a vote on a trade pact with the United States. The trade pact was ratified anyway.

Tear gas has also become a focus in Egypt, on the country’s fifth day of clashes in Cairo’s Tahrir Square. Al-Jazeera quotes a rights group as saying some have died of suffocation after inhaling the gas. Time magazine’s Cairo correspondent reports that hospitals are getting a “flood” of tear gas injuries.

And Mohamed ElBaradei, former head of the International Atomic Energy Agency and an important figure in the Egyptian revolution, tweeted Wednesday: “Tear gas with nerve agent and live ammunition being used against civilians in Tahrir. A massacre is taking place.”

The Guardian points out that a U.S. company is responsible for supplying the tear gas used in Tahrir Square.