(Bloomberg Businessweek) -- King Ng, once a healthy, 72-year-old retired mechanical engineer, now suffers from headaches so severe he often can’t sleep. He’s taken two weeks’ worth of antibiotics for an upper respiratory infection, yet his throat is still itchy and dry and he has a lingering cough.

Three months ago, Ng inhaled tear gas through the closed—but not airtight—windows of his second-floor apartment. Hong Kong police have used tear gas to quell pro-democracy protests almost every weekend and occasionally on weeknights since June 12. They’ve fired nearly 6,000 rounds in total, according to a tally of figures released in police briefings, in areas home to as much as 88% of Hong Kong’s 7.4 million residents.

On that particular day, Aug. 5, police fired 800 rounds of tear gas as the demonstrations spread through 14 of Hong Kong’s 18 districts, including Ng’s neighborhood, Wong Tai Sin, which has the territory’s highest concentration of elderly. Most of the district’s residents live in crowded public housing towers, where the median per capita income is just $21,500 a year. “We’re the lowest on the food chain here,” Ng says, shrugging. “I feel a bit angry because it’s not only the elderly people and children here, but everybody in Hong Kong is suffering from the tear gas.”

While other politically troubled areas— Cairo, Caracas, the West Bank—have been more heavily tear-gassed, according to human-rights groups, the amount used in Hong Kong is unprecedented for a tightly populated urban capital. Depending on wind conditions, building density, and where it’s released, the gas often can’t escape or has nowhere to go but up into the windows of residential tower blocks. While protesters have occasionally employed stationary tactics, including staging sit-ins at the airport, Hong Kong’s demonstrations have on the whole been unusually mobile, shifting as they move through the city—a strategy the participants call “Be Water.” Officers have chased them through parks, shopping malls, train stations, and residential areas, firing tear gas as they go. Nursing homes have been exposed, as have playgrounds.

The use of tear gas is banned in warfare under the Geneva Protocol, but allowed for riot control. Police in Hong Kong have described it as the “minimum force necessary to disperse rioters” in official statements and defended its widespread use. “In simple words, protesters chose the location, the police had to deal with them where they gathered and where they may cause violence or damage to public safety and public peace,” said Secretary for Security John Lee during a press conference the day after the Aug. 5 citywide demonstrations.

“We know that tear gas can be dangerous,” says Rohini Haar, an adviser with Physicians for Human Rights and a researcher at the University of California at Berkeley. But certain situations make it more so: releasing it into an enclosed space or where there isn’t a clear way for it to escape; firing it from above or directly into crowds, which can lead to injuries when people are struck by canisters; and using expired gas, which can be chemically unstable. “This is what happens when indiscriminate weapons are used indiscriminately,” Haar says of the tactics in Hong Kong, referring not just to tear gas but also to rubber bullets and water cannons. “They can’t stop the protests, so police think the solution is just to use more and more of them.”

Front-line demonstrators adapted by wearing gas masks, allowing them to get close enough to active tear gas canisters to extinguish them or throw them back at police. In early October, Chief Executive Carrie Lam attempted to curtail the demonstrations by invoking an emergency ordinance to ban masks during public gatherings. The plan failed: Protesters openly defied the ban, and police continued to fire tear gas.

Later that month, the U.S. House of Representatives passed a bill to ban the export of crowd control gear to Hong Kong, which include sales of tear gas. (A similar measure is under consideration in the Senate.) That followed an announcement in June by then-U.K. Foreign Secretary Jeremy Hunt that the country would suspend export licenses for crowd control gear pending an investigation, after U.K.-supplied tear gas canisters were photographed on Hong Kong’s streets. As the U.S. bill was being debated, Hong Kong police announced they had begun purchasing tear gas canisters with faster dispersal times from China, as well as longer-range launchers.

Numerous improper and potentially hazardous uses of tear gas have been captured on television or documented on social media. Riot police fired tear gas directly at protesters in the enclosed ticketing platform of a subway station in August, in violation of their own safety guidelines, prompting criticism from the United Nations Commission on Human Rights and Amnesty International. After photos of spent canisters that were past their use-by dates appeared on social media, raising more alarm, Assistant Police Commissioner Mak Chin-ho said at a news conference that expired gas posed no additional health risks and only affected the ability of the canisters to disperse gas effectively. Nevertheless, the police pledged to stop using them.

In its stable, unexpired form, tear gas causes coughing and wheezing, skin irritation and rashes, and the tears that give it its name. The process of firing tear gas canisters produces small amounts of cyanide—“not so high as to be lethal,” says Karen Mak Ka-wai, a chemistry lecturer at the University of Hong Kong. But the risk increases once they expire. When Kwong Po-yin, a doctor and district councilor in Kowloon City, surveyed 170 journalists who’d experienced heavy tear gassing while reporting from the front lines of a protest in late July—around the time the use of expired tear gas was discovered—96.2% reported difficulty breathing, persistent coughing, or coughing up blood; 72.6% had skin rashes, redness, or itching; and 40.6% said they had gastrointestinal symptoms such as diarrhea or vomiting, well beyond what would be expected from typical exposure. There’s no way to know whether these symptoms were caused by the expired gas, the high concentrations used, or a mix of these and other factors, she says.

While Hong Kong’s Hospital Authority doesn’t have official data, Kwong has gathered anecdotal reports from doctors who say they’re seeing more incidents of respiratory infections, such as bronchitis, as well as lung inflammation (pneumonitis) and coughing up blood (hemoptysis), than usual for this time of year. She says doctors from Wong Tai Sin have phoned her to ask if there’s a citywide registry where they can report their cases. So far, there isn’t. “We would like to send a message to the police force that using tear gas in residential areas is harmful,” Kwong adds. “There are babies, elderly, and all these vulnerable people.”

Research from other countries backs up the doctors’ impressions. A study of tear gas victims in Turkey published in 2014 found that upper respiratory symptoms lasted as long as 10 months in one-third of cases when the exposure occurred in enclosed areas; it also increased the risk of chronic bronchitis. Another study released in September by a group of chemical engineers in Hong Kong found that swabs from streets, train stations, and children’s playgrounds showed tear gas residue as far as 300 meters (about 985 feet) from where it was initially launched. “Even when tear gas is gone, it can still be dispersed,” says Michael Lee, who led the study. Contact with residue can cause skin irritation, and particles may be washed into gutters and enter the water supply. A letter published in the Lancet medical journal on Oct. 14 by a group of Hong Kong medical professors, warning about the long-term health effects of all the tear gas used, prompted the territory’s health minister, Sophia Chan, to say publicly that the government hasn’t detected any related irregularities in the city’s water and air quality.

Another Wong Tai Sin resident, Jerry Ip, regularly experiences the lingering effects of tear gas. When he dresses his 2½-year-old son to go to the playground, near where Ng lives, he reaches for long-sleeve shirts and long pants to protect the boy’s skin, despite temperatures that can still reach as high as 90F. Even so, his son’s hands often get itchy, Ip says. He blames the tear gas residue: “I’m sure if you were to go to the lab and check this place, you’ll find it all over here.”

Children and the elderly are particularly vulnerable to tear gas exposure, says Sven-Eric Jordt, an associate professor of anesthesiology at Duke University. “Children’s lungs are much smaller and have a smaller surface for oxygen exchange, so the same concentration of tear gas therefore causes more lung irritation and injury than in adults,” he says, adding that kids’ eyes and skin also have thinner protective layers. In the U.S., he says, police and fire departments usually decontaminate areas where tear gas was used or provide instructions for decontamination. Says Ip: “Here, no one washes it!”

Ip’s girlfriend, Apple Lam, had to admit her 1-year-old baby to the hospital after tear gas came into their 23rd-floor apartment. The windows were closed, but the air conditioning was on, sucking in the gas from outside. “He was wheezing and coughing, and you could hear he was trying so hard to breathe,” Lam says. The baby was hospitalized for three days with bronchitis; Lam still has to wash out his nose three times a day to keep his coughing under control. It’s unclear, she says, whether the baby will have permanent health problems. “I’m sad, because children are so innocent of these events,” she says.

Ng says his life has completely changed now because of the tear gas. Apart from his headache-induced insomnia and his lung troubles, he’s developed a sense of dread that’s curtailed his daily movements. “Since that event, I don’t take my walks much anymore, because I feel afraid that tear gas will suddenly be fired in the street,” he says. “Even when I see police now, I feel a little bit panicky.” —With Natalie Lung



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