With a massive network of railway tunnels passing beneath Hong Kong, the MTR requires a plethora of ventilation shafts to supply fresh air to passengers underground, and remove smoke in an emergency situation.
Early years of brutalism
Ventilation shafts built as part of the first stage of the MTR were often brutalist structures co-located with station entrances, like this shaft at Shek Kip Mei.
Shau Kei Wan.
Pitt Street in Yau Ma Tei.
Man Ming Lane in Yau Ma Tei.
Wong Tai Sin.
And North Point.
But ventilation structures were also placed away from stations if required, such as this example near Choi Hung.
One on the Tsim Sha Tsui waterfront, serving the cross harbour tunnel.
Which is paired with a second structure on the Hong Kong Island side at Wan Chai.
A more sculptural design was also used at highly visible locations along the Island Line, such as Harcourt Garden for Admiralty Station.
And outside the Western Market for Sheung Wan Station.
The construction of the Lantau Airport Railway in the 1990s saw a stylish structure erected at West Kowloon to serve the harbour tunnel.
East Tsim Sha Tsui station has a shaft on Kowloon Park Drive.
West Rail through Kowloon has a ventilation tower at Hung Hom.
Along with a larger structure on Canton Road.
An even bigger one in Yau Ma Tei.
And this massive structure at Kwai Fong – a combined traction power substation and ventilation building.
The Lok Ma Chau Spur Line has another massive structure atop the ghost station of Kwu Tung.
As does the South Island Line at the southern portal of the Nam Fung Tunnel.
But much less noticeable is the ventilation shaft at the Admiralty end, beside Hong Kong Park.
This theme of hidden ventilation structures continues at Tung Chung station.
Sai Ying Pun.
And Whampoa Station.
A space for art
Sometimes ventilation structures are turned into a feature – like the artwork ‘Sense of Green’ by Tony Ip at Admiralty Station.
Which moves in the wind.
Situated on the southern bank of Victoria Harbour in the heart of Harcourt Garden, Sense of Green is a multi-purpose sculpture that is inspired by and dedicated to the movement of air.
Externally, it comprises of several hundred bamboo-like poles that stand in the prevailing wind. As the wind increases in speed, the poles flex and bend to become stronger. The contrasting colours of the poles reflect their exposure to the wind, the paler the colour, the more frequent it has been touched by the wind.
Internally, the sculpture conceals a ventilation shaft for MTR Admiralty Station below. When viewed from the surrounding high-rise buildings above, the sculpture takes on yet another dimension – that of a super-sized potted plant that sits within the garden.
With many wanting a similar treatment applied to a ventilation structure in Tsim Sha Tsui.
You have to question why the government or the MTR have not seen fit to repaint the monstrous ventilation shaft along the newly reopened Avenue of Stars, which completely ruins everything.
I can’t believe they had close to four years to repaint it (with an epic Bruce Lee image, perhaps) during the revamp of the promenade. They should have let a street artist loose on it. It makes you wonder whether any senior government official has actually set foot on the Avenue of Stars. It is kind of hard not to notice the ventilation shaft.
Given the amount of money spent on revitalising the Avenue of Stars and given that millions of people will visit it over the coming months, I am surprised no one has raised this issue with the concerned authorities.
Readers of the SCMP offering a number of suggestions.
The need for it to be fixed up has been identified for quite some time. The MTR has yet to be forthcoming with a plan and budget for upgrading the exterior of the shaft. The simplest solution would be a lick of paint.
In the past, banners used to be displayed on the shaft, announcing arts and cultural events in the adjacent venues. So maybe the MTR is waiting for a proposal from the Leisure and Cultural Services Department. Instead of disposable banners, the vent shaft could be wrapped with an electronic billboard for such announcements. Or maybe the MTR is waiting for other people’s money and hopes New World Development will offer to hire an artist to turn the vent shaft into a large sculpture.
Or maybe it is the recent preoccupation with finding construction records that has delayed some other cool ideas the MTR has for expressing its corporate social responsibility and turning the vent shaft into a memorable moment for visitors to the Tsim Sha Tsui waterfront. Whatever happens, rest assured we will all surely see it.
Moving air through the tunnels
Massive fans are the most important part of a ventilation structure.
Along with the control system that drives them.
The Operation Control Centre confirmed with Kennedy Town's Group Station Control Room that smoke extraction mode has been engaged for the ventilation system to avoid ingesting harmful gas from street level to concourses, platforms and even into train compartments pic.twitter.com/JRab0cM9BV
— MTR Service Update (@mtrupdate) July 28, 2019
Monitored from the station control room.
As well as the MTR Operations Control Centre at Tsing Yi.
The tunnel ventilation system can adjust the flow of air outside the train when the train catches fire. According to the location of the fire alarm, the control centre will decide to change the two sets of ventilating fans on the latest train to smoke exhaust (Pull) and exhaust (Push) modes.
The convective effect produced by it will create a flow of air that once moved at a rate of about 8 kilometres per hour, blowing thick smoke in the opposite direction from the passenger evacuation route, allowing passengers to reach the nearest emergency exit as soon as possible.
The Yau Tong Ventilation Building serves the Tseung Kwan O Line, and in 2018 the MTR Corporation sold the land atop it to a developer for HK$1.515 billion (US$193 million), who will build a 500 apartment tower on the site.
And an interesting impact on train operations
Running a frequent train service depends on many things, but one I didn’t consider is the tunnel ventilation system – the ‘MTR Service Update’ blog has the full story.
Under normal circumstances, the piston effect of the train will drive the air in the tunnel. However when the train is stopped between two stations for more than about two minutes, a large fan in the ventilation building will be activated.
Through the ventilation openings near the top of the tunnel or at the bottom of the platform, heat from the air conditioners and various equipment on the train roof will be taken away. The system will maintain the temperature in the tunnel not higher than 35 degrees, to prevent the air conditioner from being able to dissipate heat in the car.
However, tunnels passing under Victoria Harbour were constructed in caissons, with limited space inside the tunnel, making it difficult to build additional air ducts for ventilation fans. Therefore, one direction of the tunnel can only accommodate one or two trains at the same time. Longer distance tunnels, such as the Chau Tau Tunnel between Sheung Shui and Lok Ma Chau Station, have the same restrictions.
The signal system will also prevent the third train from entering the tunnel, and the train captain will broadcast a “train service blocked” message to inform passengers that there is still time to enter and exit the carriages. The Beacon Hill Tunnel between Kowloon Tong and Tai Wai Station has increased in frequency from 15 trains per hour in the single direction (at the beginning of the electrification of trains) to the current 24 trains, after additional ventilation facilities were added.