Using computer fluid dynamics, Forensic Architectur and Imperial College London simulated the movement of CS particles across downtown Portland as a result of the actions of Portland’s police. Credit: Forensic Architecture
In summer 2020, many cities protested in response to the police murder of George Floyd. In most places, police and protestors clashed further during these days and nights.
In Portland, protests went on for months. During this time, the Portland Police Bureau (PPB) repeatedly used tear gas to move protestors from sections of the city, including from in front of their headquarters. One specific summer night—June 2, 2020—the PPB released large amounts of tear gas on a day that would become known locally as “Tear Gas Tuesday.”
Now, researchers at Forensic Architecture and Imperial College London have used computer fluid dynamics to reconstruct and simulate the spread of the toxic chemicals in tear gas as they moved across downtown Portland that night.
The team found that the toxic tear gas cloud caused airborne chemical concentration levels 2,000 times higher than the acceptable level, set by OSHA.
Levels considered ‘immediately dangerous to life and health’
Drawing on publicly available information, like social media videos and news reports, the researchers counted, located and identified the different munitions used by the PPB on June 2. Chemically, they focused on the identification of CS, or o-chlorobenzylidene malononitrile, one of the most commonly used chemicals in tear gas.
According to the research, between 9:00 p.m. and 12:00 a.m., the PPB used at least 148 munitions, of which 138 were likely chemical munitions.
The researchers studied 15 different locations across downtown Portland, some in immediate proximity to protest sites and others further away. In 19 separate instances across the locations, OSHA’s 2 mg/m³ threshold was exceeded continuously for more than 1 minute. Throughout the night, across all locations, concentrations of 2 mg/m³ were exceeded for a total of over 73 minutes.
The simulation recorded the highest airborne concentration level at 4,568 mg/m³—more than 2,000 times the limit set by OSHA. That sampled location was just one block north of an intersection considered to be a key location in the protests—one that saw its own maximum airborne concentration reach 443.9 mg/m³ for 6 minutes and 20 seconds.
The simulation results showed the use of tear gas was concentrated within three peaks during the 3-hour time period. The first peak lasted 18 minutes, the second peak lasted 24 minutes and the third peak lasted 28 minutes.
“Within each of these peak periods, an array of different emission type was used, which in turn produced significant clouds of airborne toxic chemicals and depositions in varying concentrations on the ground,” said Forensic Architecture researchers.
Not just the air
Indeed, the simulation suggests that CS particles would have carried more than 809 meters across Portland on that day, following the prevailing winds, as well as hanging suspended between buildings in downtown Portland for hours afterward.
Just about a year later, in May 2021, Kaiser Permanente Center for Health Research published the results of a study showing the health impacts on the general population from the use of tear gas during the previous summer’s protests.
Kaiser, which is based in Portland, surveyed more than 2,000 people of various ages and health conditions. Ninety-four percent of the 2,200 who responded to the survey reported a health impact from tear gas, and over 1,200 people sought out some type of care after being exposed. More than half of the applicable respondents reported changes to their menstrual cycles. Breathing issues was also a highly cited symptom. Asthma, lung injury and neurodegeneration have all been linked to the toxic chemicals in tear gas in previous studies.
Lastly, according to the simulation, more than 2 kg of CS would have been deposited in the Willamette River on June 2 alone. The river is home to a variety of aquatic species for whom CS is highly toxic.
The full visual investigation is available on the Forensic Architecture website.
In November 2022, the city of Portland reached a $250,000 settlement to a federal lawsuit over PPB’s use of tear gas and other crowd control devices during the Summer 2020 protests.