UVC Sterilisation Device Fends Off Virus Transmission Through Pipes

Simulated image of installing the UVC sterilisation device on a rooftop ventilation pipe

The outbreak of COVID-19 in the community, in particular the infection cases in Heng Tai House, Fu Heng Estate in Tai Po last March has once again raised concerns about the hygiene risks from drainage pipes. Experts suspected that the spread of virus was a phenomenon of the “wake effect” which might have occurred on the rooftop where air turbulence may bring the virus from the ventilating pipe outlets of soil and waste stacks into residential units. To lower the risk of infection arising from drainage pipes, the URA has invited and supported a team of experts to develop the UVC (Ultraviolet-C) sterilisation device for connecting with ventilating pipes on the rooftops to ensure all air vented out the building is sterilised.

Prof Lam Chun-yu says the team decided to adopt UVC as the disinfection method due to its convenience and effectiveness in energy saving.

The newly developed UVC sterilisation devices are connected to the ventilating pipe outlets of soil and waste stacks, whose purpose is to equalise the air pressure inside the drainage system to avoid the “Siphon effect” or “Siphonage”. As toilets of different units in a building are connected to the same soil and waste pipe, when someone flushes the toilet, the subsequent negative suction may drag water out of the U-trap. Hence it is important for air to flow in through the roof ventilating pipes to balance the air pressure and prevent the water seal of the toilet from being broken. Open to atmosphere, the vent pipe usually allows entry of air to make up for any reduction of air pressure in the drainage system, but when wind incidentally blows through the pipe end forming a turbulence, air carrying the virus may leak out from the soil and waste pipe.

Associate Professor of Civil Engineering Department of Chu Hai College of Higher Education Ronald Lam Chun-yu, who is also responsible for the project, said test results have proven that the UVC sterilisation device effectively kills 80 to 90% of the virus in pipes, including the novel coronavirus (tested by Pseudo virus). Elvis Hui, Senior Manager (Works & Contracts) of the URA said the Authority is seeking approval from Government departments to install the devices on the roofs of Central Market and Soy Street rehousing block for on-site trials. Performance data of the sterilisation devices are to be collected for further modification on the design before a full launch of the device will take place in the future.  

Cross section view of UVC sterilisation device