Republican Senate candidate Manny Sethi speaks at a campaign event held at Southern Railway Station in Knoxville, Tenn., on Friday, July 24, 2020.

Republican U.S. Senate candidate Bill Hagerty speaks to supporters on Friday, July 17, 2020, after casting an early voting ballot at the Nashv…

The use of tear gas to control crowds has soared in recent years. But researchers say most of what we know about its health effects is based o…

FILE - In this July 26, 2020, file photo, federal officers launch tear gas at demonstrators during a Black Lives Matter protest at the Mark O.…

FILE - In this July 26, 2020, file photo, a federal officer holds a tear gas rifle during a Black Lives Matter protest at the Mark O. Hatfield…

FILE - In this July 29, 2020, file photo, a demonstrator kicks a tear gas canister back at federal officers during a Black Lives Matter protes…

FILE - In this Nov. 30, 1999, file photo, Seattle police use tear gas to push back World Trade Organization protesters in downtown Seattle. Th…

FILE - In this Aug. 27, 1968, file photo, a woman wears a gas mask as she walks with a companion holding a cloth to his eyes after they were s…