Health officials must come clean about harmful effects of tear gas so Hong Kong can breathe easy again

The official downplaying of tear gas effects – comparing it to barbecue fumes, for example – is worrying, given the body of science warning of serious, even fatal, health risks
The recent switch from using US tear gas to Chinese-made canisters also makes it more urgent to answer the question of what exactly the city is being exposed to

Martin Williams

Published: 9:30am, 21 Dec 2019

Why you can trust SCMP

Though it is just weeks since I experienced tear gas, the memory of it is a bit of a blur. One minute, I was among a group watching riot police approach Central, the next, someone appeared beside me and threw a petrol bomb, prompting instant bangs as tear gas canisters were fired towards us. Along with the others, I headed for a side street.

I was just in time to escape the worst of the tear gas. Still, my eyes stung, there was a lingering acrid taste in my mouth and my throat felt unpleasantly dry.

Days before writing this article, I had a very different experience at a Sai Kung barbecue site, where around 100 schoolchildren lit charcoal and barbecued meat, overseen by teachers. None seemed flustered by the smoke.

This seems normal: tear gas is a chemical weapon; countless people enjoy barbecues. But, remember that earlier this month, Welfare Secretary Law Chi-kwong replied to a question about tear gas safety by saying it only causes mild respiratory and skin irritations. “In fact, when compared with dioxins resulting from our barbecue activities, I think the level is indeed very minimal,” he added.

This followed Secretary for Food and Health Sophia Chan Siu-chee saying the government had found no evidence that tear gas can cause dioxin poisoning, and the police have been sourcing safe ammunition. She also noted that people exposed to tear gas generally experience mild respiratory and skin irritations.

Was Professor Chan, formerly director of research at Hong Kong University's School of Nursing, being economical with the truth? Even a simple review of scientific research on tear gas effects reveals they can be far more serious, even fatal, on top of the dangers of being struck by the canister.

According to a 1989 paper in the Journal of the American Medical Association: “Tear gas is actually the common term for a family of chemical compounds that have been otherwise referred to as ‘harassing agents’ because of their ability to cause temporary disablement.”

The main chemical used in most tear gas is o-chlorobenzylidene malononitrile – commonly known as CS gas. The paper noted it can cause lung inflammation and fatal pulmonary oedema – lung tissue swelling so severely it can cause death. High exposure levels have reportedly also led to heart failure and liver damage.

Two years ago, an extensive review of the health effects of tear gas and pepper spray concluded that they “cause severe injury, permanent disabilities, and in rare cases, death”. The authors considered that children, elderly people and people who frequently attend protests were especially at risk.

A Turkish study on long-term effects found that, even in the year after exposure, there were high rates of respiratory complaints, along with the risk of chronic bronchitis.

As yet, there are no such studies for Hong Kong. But in a local online survey of tear gas effects on children, more than 1,000 mothers reported coughing (65.1 per cent), a dry throat (55.5 per cent), nausea (11.5 per cent) and vomiting (9.4 per cent). The children were, on average, just six years old.

In October, four public health academics at the Chinese University of Hong Kong wrote in The Lancet about their concerns regarding tear gas use in Hong Kong. They said the situation “calls for a reflection of the appropriateness of tear gas utilisation for crowd and riot control in densely populated urban areas”.

They also recommended that the government invest in tear-gas-related health surveillance and long-term environmental monitoring. Their criticism was rejected by Chan.

The truth about tear gas: how Hong Kong police violated guidelines

The government also says the chemical composition of the tear gas is secret. The supposed justification is “police operational reasons”, which seems a flimsy excuse and in disregard of public health.

It is more likely that the secrecy is on behalf of manufacturers keen to protect their tear gas recipes. This includes the concentration of ingredients such as magnesium oxide and aluminium involved in rapid reactions that generate the heat needed to vaporise and spread the tear gas, which is really a solid at ordinary temperatures.

There may be special cause for concern about the recipes used in Chinese-manufactured tear gas canisters, which were introduced here in October. Their reactions are even hotter and faster than the US-made canisters previously common – intrepid researchers with local TV channel HKGETV recorded temperatures of up to 552 degrees Celsius with Chinese-made canisters, around 150 degrees hotter than for American versions.

These high temperatures spurred concerns that they could produce dangerous levels of dioxins, which can accumulate in the body and cause problems, including cancer.

This seems unlikely, maybe even a red herring. Professor Chan King-ming, of the Chinese University of Hong Kong's School of Life Sciences, collected samples from the zone where police battled protesters at the university, and detected only tiny amounts of dioxins, well below safe levels. This accords with the Leisure and Welfare Bureau's reply to an inquiry I emailed, listing six reports on decomposition of CS gas, none of which detected dioxins.

However, the decomposition studies did find that chemicals, including hydrogen cyanide, were produced, with the variety increasing as temperatures rose, leading the authors of one paper to recommend, “a delivery system designed to contain the molten CS and maintain a consistent temperature near 150 degrees C” – much cooler than the HKGETV team observed.

Health fears over use of tear gas by police must be confronted

The HKGETV team also checked spent canisters for CS gas, and while they found a fair concentration in an American canister, there was little in one from China, and none at all in another Chinese canister. Perhaps the Chinese canisters get so hot, all the CS gas disintegrates. Or, just possibly, other tear gas chemicals are used – such as CR gas, so potent it is nicknamed “firegas” and which is not employed in the US as it is carcinogenic.

This may be a ludicrous notion; but who knows, given the secrecy? If Chan knows, she is keeping quiet about it. With some 16,000 tear gas canisters fired during six months of protests – including indoors, and often in confined streets, perhaps it is time for our health officials to be more candid.

Martin Williams is a Hong Kong-based writer specialising in conservation and the environment, with a PhD in physical chemistry from Cambridge University

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