After Hong Kong police fired 800 tear gas canisters at umbrella-wielding demonstrators on a single day… hundreds of empty aluminum shells littered the streets in the wake of the protests. Many of those shells were made in the Keystone State.

Pennsylvania is a leading manufacturer of tear gas, exported all over the globe. Combined Systems Inc. of Jamestown, south of Erie, and Nonlethal Technologies of Homer City, east of Pittsburgh, are among the top five companies in the world producing “riot control systems,” according to Visiongain, a market research firm based in London…

A spokesperson for Combined Systems, which also makes high-capacity Venom brand grenade launchers, did not return calls for comment. Combined Systems is owned by the Carlyle Group, which manages $13 billion in global assets. Michael Scott Oberdick and James A. Oberdick, the owners of Nonlethal Technologies, also declined to comment…

What police and protesters call tear gas is not a gas at all, said Anna Feigenbaum, a professor at Bournemouth University in England who wrote Tear Gas: From the Battlefields of World War I to the Streets of Today. Rather, the chemical compounds are toxic powders that are aerosolized as a fog or spray.

“They are designed to attack the senses simultaneously, intentionally producing both physical and psychological trauma,” said Feigenbaum. “It acts as an irritant on multiple sites of the body at once, primarily affecting mucous membranes and respiratory system.”…