Use of tear gas for crowd control in Hong Kong

By Emily Ying Yang Chan, Kevin Kei Ching Hung, Heidi Hoi Yi Hung, Colin A Graham

Heated debates over the Fugitive Offenders and Mutual Legal Assistance in Criminal Matters Legislation (Amendment) Bill 2019 introduced by the Hong Kong Special Administrative Region Government have led to numerous public marches and demonstrations since June 9, 2019.

Subsequently, the methods used by the Hong Kong Police Force to manage the protests and outbreaks of public violence have become highly controversial. Over 3000 rounds of tear gas have been deployed as crowd control agents by police since June.

The tear gas used by the police contains o-chlorobenzylidene malononitrile, an irritant that interacts with mucocutaneous sensory nerve receptors, including TRPA1 channels, and causes rapid clinical effects with a wide margin between the incapacitating dose and the lethal dose. Although brief in duration, clinical manifestations include tearing and burning sensations in the eyes, cough, dyspnoea, skin rashes, blistering, hypertension, nausea, vomiting, and agitation.

Authors of a systematic review, including 5910 people exposed to chemical irritants, reported two deaths and permanent disabilities such as blindness, vegetative state from traumatic brain injury, amputations and loss of limb function, psychiatric sequelae including post-traumatic stress disorder, persistent respiratory complaints including asthma, and chronic dermatological conditions occurred in 58 people. However, data on long-term sequelae, carcinogenicity, and environmental consequences in the urban context are scarce.

Perhaps one of the main public health controversies is the apparent absence of government-led decontamination efforts and the absence of official guidelines and self-help advice on health protection against the side-effects of tear gas. In the hot and humid subtropical environment of Hong Kong, tear gas deployment in enclosed spaces such as busy railway stations and near commercial shopping centres can expose people to high concentrations of tear gas for a prolonged amount of time. Tear gas has also been deployed in high-density residential areas and communities with many elderly people (eg, Kwun Tong, Wong Tai Sin, and Sham Shui Po). Affected communities and premises have to find their own way of decontaminating their surroundings.

The ongoing situation in Hong Kong calls for a reflection of the appropriateness of tear gas utilisation for crowd and riot control in densely populated urban areas when minimum efforts have been made to provide decontamination guidelines and health protection to bystanders, affected communities, and stakeholders. The Hong Kong SAR Government should invest in tear gas-related health surveillance and long-term environmental monitoring.

Source: The Lancet, 26 October 2019