There is a second such shaft at 783 Nathan Road in Prince Edward with a convenience store on the ground floor. They are the only two of their kind, built between 1975 and 1980 as part of Hong Kong’s first MTR line. But before we dive into the factors that led to their creation, let us first deal with the basics. How do ventilation shafts work?

Air in, air out: the basics of underground ventilation

Ventilation shafts bring fresh air down into the MTR, and draw foul air out. This “foul” air is not heavily polluted as the trains run on electricity, not combustion engines. However, it contains the accumulated carbon dioxide, water vapour, body odours, and toilet smells generated by millions of commuters. It also carries heat emitted by the trains’ cooling systems. Ventilation shafts are essential to keeping people cool and comfortable underground. When the system was first designed in the 1970s, engineers worried that in Hong Kong’s hot climate, temperatures would become unbearable within six minutes if a train were delayed in a tunnel. To avoid this scenario, they negotiated an agreement between China Light and Power and Hong Kong Electric to supply back-up power on opposite sides of the harbour in case of a power cut. 

Ventilation shafts are also part of the fire safety system. If a train catches fire, powerful fans extract the smoke and pump in fresh air. The MTR’s control rooms are programmed with a number of protocols for turning fans on and off in different situations.  

However, the fans are not used during normal operations. The system uses the movement of the trains to push air around. As a train speeds through a tunnel, it pushes the air in front like the plunger of a syringe, forcing it out of the ventilation shaft up ahead. Meanwhile, air rushes in from the ventilation shaft behind to fill the gap left by the train.

This means that ventilation shafts cannot be placed anywhere, but must be located close enough to the tunnels for the air pressure differential to have effect. Tunnel ventilation shafts are set up in pairs at either end of each MTR station, i.e. at the beginning and end of each tunnel segment. If a tunnel is very long, an extra shaft is added in the middle. Since each line has two tunnels carrying trains in opposite directions, each station has four shafts. There is also a third pair to serve the station’s air-conditioning system, bringing the total to six.

Current regulations state that MTR ventilation shafts should be at least 3m above the pedestrian level, and at least 5m away from nearby buildings. Air intakes should also be at least 5m away from air outlets, to avoid drawing the foul air back underground. 

How to hide a ventilation shaft in public

Andrew Mead, Head of Architecture at the MTR Corporation, says that the challenge faced by the MTR’s architects is figuring out how to integrate these large, ugly structures into the urban environment. These days, the MTR often merges them into station entrances so that they look like part of the building.  

Senior Project Architectural Manager Cheng Kwok-wai points out ones that have been given artistic flourishes. At Harcourt Garden in Admiralty, there is one outfitted with a forest of green metal tubes, giving it the look of a giant potted plant. On the Tsim Sha Tsui waterfront, the massive shaft serving the cross-harbour line has been painted to echo the textured facade of the Museum of Art.  

However, back in the 1970s, there was no budget for aesthetics. While the MTR famously pioneered a “rail-plus-property” financing model, the first line from Kwun Tong to Central was built on a tight budget of HK$5.8 billion provided by the Hong Kong Government. After being postponed for several years, the line was built in just five years, slicing through the heart of Kowloon with ruthless pragmatism. Engineers contended with a multitude of problems. Below ground, they encountered flooding, crumbly unstable soil, old reclamation seawalls, boulders, and a tangle of poorly mapped power cables, gas lines, and water mains. (Many maps of utility lines had been destroyed during the Japanese occupation.) Above ground, verandahs were removed from buildings so that heavy equipment could be placed on Nathan Road. Steel frames were suspended over excavation pits so that traffic could keep flowing. Rows of buildings were demolished to provide MTR work sites.

According to Mead, the MTR’s chief architect at the time, an Anglo-Italian named Roland Paoletti, found little scope for creativity in designing the stations, aside from choosing a different colour for each one. Where he did have some fun was in designing the ventilation shafts, using simple geometric shapes arranged with a whimsical sense of proportion. Still, his earliest ones were basic rectangular boxes. His more playful designs only started appearing on the Island Line in the early-to-mid 1980s. 

How to hide a ventilation shaft on private property

When suitable spots could not be found on government land, the MTR placed ventilation shafts on private property. The ventilation shaft at 783 Nathan Road appears to have been built on a former MTR work site, and at 308 Nathan Road,  a six-storey building was demolished just for this purpose. 

HKGP Surveyor (我係 “橙葉測量師”), who runs a popular Facebook account about building issues, found that 308 Nathan Road was given to the MTR under a private treaty grant in 1980, and that its land lease actually required the MTR to construct a non-industrial building costing at least HK$100,000. The shop was built to fulfill the requirement. In other words, having acquired the site for the MTR, the government required them to make some economic use of it. However, standalone shafts on private land must not have been very cost-effective, as they do not appear on later lines. 

A more common early strategy was to find a site that was being redeveloped and compensate the owner for the inclusion of a ventilation shaft. For example, in 1979, the MTR paid the owner of 221B & C Nathan Road $100,000 for a 6 month delay plus additional construction costs incurred to their project. The shaft is now hidden in a back alley behind an office building, and several others exist in Jordan, Prince Edward, Sham Shui Po, and Wanchai. A similar strategy was to take a corner out of a private lot, forcing the developer to build around it. Examples can be found in Jordan, Lai Chi Kok and North Point.

These shafts were given even less aesthetic consideration than those on public land, but this paradoxically seems to have made them more invisible. They are so nondescript that the mind skips over them.

Over time, these less elegant solutions were abandoned in favour of fully integrating ventilation shafts into building podiums, either in properties developed by the MTR, or by requiring other developers to accommodate them through planning conditions.

This was done in a couple of places on the first MTR line, i.e. at Argyle Centre Phase II in Mong Kok, which was jointly developed by Hang Lung, Cheung Kong and the MTR; and the Landmark in Central, which was developed by Hong Kong Land. It became more common on the Island Line; ventilation shafts are hidden in Southorn Centre, Sogo, and the Sai Wan Ho Market and Cooked Food Centre, to name a few. All that is visible is a grille on the side of the building, and unless you go looking for unexplained voids in the floor plans, you would never know they are there. 

Sources

Special thanks to Andrew Mead, Head of Architecture; and Cheng Kwok-wai, Senior Project Architectural Manager of the Mass Transit Railway Corporation. 

Colin Coulson, “The birth of the MTR: a personal recollection,” Journal of the Royal Asiatic Society Hong Kong Branch, vol. 59 (2019), pp. 200-208.

Christopher DeWolf, “The MTR turns 45: How it all began,” Zolima Citymag, 10 October 2024.

Mass Transit Railway Corporation, “Iron Underground: The Building of a Railway,” video documentary, MTRC, 1986.

Andrew Saint, “Roland Paoletti Obituary,”, The Guardian, 15 December 2015.

我係 “橙葉測量師”,〈彌敦道嘅單層地舖〉, Facebook post, 22 May 2021.