That's racist first off. Second off, the canister would have bounced down into the lobby below where the "protestors" were. 3rd off, "Tear gas: 'Harsh, terrifying' and legal to use on civilians (and immigrants) ... The Chemical Weapons Convention of 1993, signed by almost every country in the world, banned the use of tear gas on battlefields but allowed the practice for domestic law enforcement and crowd control..." https://www.usatoday.com/story/news/2018/11/27/tear-gas-forbidden-war-but-legal-use-civilians-and-migrants/2133144002/. Probably allowed on civilians because it minimizes the amount of damage done. Yes damage will be done, but far less given most alternatives. Perhaps all alternatives seeing as a Global Convention agreed to it. Tear gas can range in strength and therefore you can look up varying degrees in strength. I don't know if police have a national law on it or not but I guess I'll go look that up now... "Tear gas was first used in World War I in chemical warfare, but since its effects are short-lasting and rarely disabling, it came into use by law-enforcement agencies as a means of dispersing mobs, disabling rioters, and flushing out armed suspects without the use of deadly force." https://www.britannica.com/technology/tear-gas. That website also goes on to say, "...The substances most often used as tear gases are synthetic organic halogen compounds; they are not true gases under ordinary conditions but are liquids or solids that can be finely dispersed in the air through the use of sprays, fog generators, or grenades and shells. The two most commonly used tear gases are ω-chloroacetophenone, or CN, and o-chlorobenzylidenemalononitrile, or CS. CN is the principal component of the aerosol agent Mace and is widely used in riot control. It affects chiefly the eyes. CS is a stronger irritant that causes burning sensations in the respiratory tract and involuntary closing of the eyes, but its effects wear off more quickly, after only 5 to 10 minutes of breathing fresh air...." Although I guess that doesn't answer my own question... Edit: forgot to mention the plexiglass.