https://arstechnica.com/science/2020/06/tear-gas-is-more-dangerous-than-police-let-on-especially-during-the-pandemic/

When Amira Chowdhury joined a protest in Philadelphia against police violence on Monday, she wore a mask to protect herself and others against the coronavirus. But when officers launched tear gas into the crowd, Chowdhury pulled off her mask as she gasped for air. “I couldn’t breathe,” she said. “I felt like I was choking to death.”

Chowdhury was on a part of the Vine Street Expressway that ran underground. Everyone panicked as gas drifted into the dark, semi-enclosed space, she said. People stomped over her as they scrambled away. Bruised, she scaled a fence to escape. But the tear gas found her later that evening, inside her own house; as police unleashed it on protesters in her predominantly black neighborhood in West Philadelphia, it seeped in.