Study says Portland tear gas concentrations far exceeded safe levels in 2020

By Jonathan Levinson (OPB)
April 17, 2023 2 p.m.
Police use tear gas and impact munitions to disperse protesters in downtown Portland during 4th of July demonstrations against systemic racism and police violence.

FILE: Police use tear gas and impact munitions to disperse protesters in downtown Portland during demonstrations against systemic racism and police violence on July 4, 2020.

Jonathan Levinson / OPB

For 13 minutes during a June 2, 2020, racial justice protest, the concentration of tear gas particles at one downtown Portland corner was high enough to cause severe, irreversible health effects, according to a study released today by the human rights research group Forensic Architecture.


The Occupational Safety and Health Administration says anything over 2mg per meter cubed of what’s usually known as CS gas, the most common of the three varieties of tear gas the Portland Police Bureau uses for crowd control, is immediately dangerous to life and health. At the corner of Southwest 5th Avenue and Yamhill Street that night, Forensic Architecture estimates the tear gas concentration reached 443.9mg per meter cubed, more than 220 times the safe limit.

An hour later, one block away, estimated levels briefly hit more than 2,200 times the safe limit.

The findings are the result of a yearslong study by Forensic Architecture, an organization based at Goldsmiths University of London. The group collected hundreds of videos from the June 2 protests, which became known among activists as “Tear Gas Tuesday,” and reconstructed three hours of the night as protests moved throughout downtown and police declared an unlawful assembly. As police tried to disperse the estimated 1,000 demonstrators on the streets that night, Forensic Architecture determined, Portland police fired at least 138 chemical munitions throughout an 18-block area.

“The Portland Police Bureau used tear gas against civilian protesters in quantities which very likely significantly exceeded federally-recognised safe levels of airborne CS concentration for human exposure,” Forensic Architecture’s methodology report says. “At every location sampled by our methodology, those safe levels were exceeded.”

Portland Police use three different types of “riot control agents,” colloquially known as tear gas, that can be fired into crowds via eight different weapons systems. Those include a rifle that shoots small plastic projectiles designed to release a tear gas agent when they shatter and grenades that disperse three tear gas canisters 20 feet in different directions when they detonate.

Weapons experts used public records cataloging which munitions the bureau keeps on hand and hours of video to estimate which types of chemical munitions were likely used in each instance.

Bob Trafford, an assistant director at Forensic Architecture, explained that because even the best modeling will deviate from reality, researchers intentionally low-ball their estimates.

“There are a lot of points where we can say, ‘OK, we have diverged from the real conditions in some respect,’” Trafford said. “You have to diverge an enormous amount, far, far more than we believe that we have, to have made a mistake in which this was not … routinely 50 times the immediate danger to life and health level.”

Even if you halve all of the findings, he said, the results still far exceed safe thresholds.

A computer model of Downtown Portland shows estimated CS gas concentration levels during a racial justice protest on June 2, 2020.

A computer model of Downtown Portland shows estimated CS gas concentration levels during a racial justice protest on June 2, 2020.

Forensic Architecture / OPB

The Portland Police Bureau did not respond to questions about whether officers are trained on safe CS concentration levels and how or if they monitor those levels when using tear gas. A spokesperson said they could not comment because there is still litigation pending from 2020 protests.

According to Defense Technology, the company that makes most of the munitions Portland uses, CS gas can cause blisters, asthma attacks, shortness of breath, chest tightness and feelings of panic.

Safe levels of tear gas toxicity have historically been tricky to measure. Dr. Rohini Haar, an emergency room physician and researcher at the University of California, Berkeley School of Public Health who has reviewed the new study, said standards for safe levels come from laboratory research with rats or other animals.

“To translate that into how much a person is inhaling, is challenging,” she said. “That’s why you’re going to see lots of different kinds of reactions and injuries. Even if everyone has the same exact exposure in a room, every single person is going to have a different reaction.”


She said that doesn’t mean people will necessarily need to go to an emergency room or require medical treatment. Throughout the 2020 protests, people reported various health impacts they believed were connected to tear gas exposure.

A 2021 study by Portland’s Kaiser Permanente Center for Health Research found that over half of the 1,650 respondents who potentially menstruate had their cycle impacted in some way. People described having itchy eyes and a scratchy throat when walking in areas where tear gas had been used the night before. Other research into tear gas’ side effects have found it can cause inflammation and organ injury, and it has been linked to pregnancy loss in Bahrain and Chile.

“Tear Gas Tuesday” came just a few days into what went on to be nearly 200 days of sustained protest against police violence in the city. The protests were sparked by George Floyd’s murder at the hands of then-Minneapolis police officer Derek Chauvin.

Media reports from that night described the Portland Police as being in a “tear gassing fury,” and an “indiscriminate barrage of grenades, kettling the crowd on all sides with walls of tear gas.”

“Gas and bangs everywhere,” an OPB reporter tweeted, referring to flash bangs, the loud concussion devices police use to disperse crowds.

The widespread use of tear gas that night horrified some city officials. Then-city Commissioner Chloe Eudaly said it was sadistic.

“I went to bed in tears, watching police fire gas canisters as they were rolling down streets into random crowds of protesters,” she said. “I woke up horrified by images that were shared with me this morning.”

Then-Commissioner Jo Ann Hardesty called the images heartbreaking.

Then-Police Chief Jami Resch, who would step down five days later, defended the response, explaining that some people in the crowd gathered at a fence surrounding the Multnomah County Justice Center had thrown projectiles at officers.

Portland Mayor Ted Wheeler said police “are doing everything they can within their power to respect and protect peaceful demonstrators.”

Police bureau policies require officers to consider their proximity to homes, hospitals and schools before using tear gas and to minimize impacts on people who are not being targeted.

“Our simulation, however, reveals how tear gas use is indiscriminate,” a Forensic Architecture video released with the study explains. “Chemicals deployed by the PPB spread widely across downtown Portland.”

Days after the night Forensic Architecture studied, U.S. District Court Chief Judge Marco Hernandez issued an injunction restricting the police bureau’s use of the chemical agents, finding that officers had likely used them to disperse peaceful demonstrators. In December 2020, Hernandez found the city in contempt for violating the injunction. The lawsuit, brought by five protesters and the group Don’t Shoot PDX, which led to his order was settled in November for $250,000.

Later in the summer of 2020, Portland became a national flash point when federal law enforcement officers, deployed to the city at the behest of then-President Donald Trump, unleashed extraordinary levels of violence against the thousands of people gathered downtown in front of the Multnomah County Justice Center and federal courthouse. Unrestrained by the federal court order, those officers deployed tear gas frequently and once again filled downtown Portland streets with chemical gas.

The Portland Bureau of Environmental Services took samples from storm drains near the epicenter of the protests in 2020. The agency found elevated levels of barium, copper, lead and zinc in storm drains near the downtown federal courthouse but said those levels subsided by the time they reached the river.

Forensic Architecture’s modeling, however, estimates approximately 2 kilograms of the toxic chemicals were likely deposited in the Willamette River on June 2 after drifting through the air from where they were initially used.

Forensic Architecture conducted a similar analysis of tear gas use against protesters during a December 2019 demonstration at Plaza de la Dignidad in Santiago, Chile. They found levels there were more than 40 times what the Chilean police said constituted a serious danger to physical health. And in 2021, the group worked with lawyers and activists to construct an interactive presentation showing how the Palestinian residents of Sheikh Jarrah are being displaced from their land.