- David Hui, chairman of the department of medicine and therapeutics at Chinese University, says some police forces do not follow manufacturers’ guidelines
- Improper use of the crowd-control weapon can do great damage to people’s health and sometimes even be lethal, he warns
An expert in respiratory medicine warned on Wednesday that improper use of tear gas could turn the non-lethal crowd-control agent into a deadly weapon and urged law enforcers in Hong Kong to draw up guidelines to ensure the safety of those targeted.
Professor David Hui Shu-cheong, chairman of the department of medicine and therapeutics at Chinese University, was referring to the more than 1,800 rounds of tear gas fired during protests against the now-shelved extradition bill since early June.
Some tear gas canisters were fired in residential areas, near elderly homes and transport hubs, drawing criticism that the force had endangered people's health and even lives.
Hui said that according to the manufacturers' safety guidelines, tear gas should not be fired indoors but that police in Hong Kong and in some other countries did not always follow the advice.
"Proper use of tear gas in an open area can be a very effective way of dispersing crowds," Hui said. "However, improper use can do great damage to people's health and sometimes even be lethal."
He cited police's use of tear gas inside an MTR station as an example.
"It's not proper to do so because the concentration of tear gas will be much higher inside a poorly ventilated space," Hui said.
"Also, if someone, say protesters, staff or merchants from the station, happen to stand near where the police fire the tear gas, its impact force, if it hits anyone in the neck or head, can be lethal."
Police fired tear gas in Kwai Fong MTR station on the night of August 11 when trying to clear anti-government protesters. The move angered many residents because of the chaos and potential health risks associated with the highly concentrated smoke.
The following day police said they fired only one round of tear gas and the station was semi-enclosed.
Hui said: "The spot where police fired tear gas was open area, but it was dispersed towards an enclosed space. This was wrong."
It was especially dangerous for those with respiratory problems such as asthma, which could be triggered by strong tear gas, he added.
Chaos at Yuen Long MTR station as protesters confront police after sit-in
Hui also warned of the risk of hitting people when firing the substance. "Tear gas should be dispersed at the edge of a crowd and below knee level to avoid hitting people," he said.
He said firing close to residential areas would do more damage to the health of the elderly because they often had respiratory illnesses. Children would also suffer more because tear gas, heavier than air, eventually sank to lower ground.
Police also admitted they used expired tear gas.
Hui said a study on using an expired type in Egypt showed that the launching effect was weakened while a US military report in 2010 showed that tear gas fired at the temperature of 275 degrees Celsius released toxic cyanide.
"So I think whether cyanide is released or not is more related to the temperature than expiration date," he said.
Jenny Cheung, president of the Hong Kong Pharmacists Union, shared the same concerns on the effects of tear gas on residents. "We are very worried that the dispersed poisonous chemicals from fired tear gas are affecting communities."
Angry residents gather at Hong Kong stations to demand tear gas answers
Cheung said the chemical activity of tear gas could last as long as five days and it was possible that chemical residues remained attached to objects and the ventilation system inside stations making them hard to clean.
She urged the government to close affected stations to thoroughly clean them, especially ventilation systems, because tear gas could be carcinogenic.
Hui said he believed the density of the tear gas chemicals would be low after so many days and that using soapy water to clean up the stations should suffice.
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