Pedestrians walking by a military pier near the Central waterfront could be at the mercy of toxic fumes from People's Liberation Army warships moored there, health experts and environmentalists warn.
Warships are likely to be exempted from a law that would require ocean-going vessels to use cleaner fuels while at berth in the city's waters.
A 150-metre site near the PLA barracks in Admiralty will officially be rezoned from public open space to military use when it secures approval from the Executive Council later this year, despite a public outcry.
Professor Anthony Hedley, the public health specialist behind the Hedley Environmental Index, said heavy concentrations of high-sulphur fuels - or bunker fuels - close to a densely populated area like Central would be especially harmful due to prolonged exposure levels.
"If [Hong Kong] is really serious about cutting emissions then this will certainly be an impediment," Hedley said. "It doesn't make sense to add more to pollution when every cubic metre more of polluted air will only add to more serious disease, deaths and higher health costs."
Hedley warned of the toxicity of heavy bunker fuel emissions, which besides particulate matter and sulphur dioxide, also contain heavy metals such as nickel. The sulphur content of low-grade bunker fuel burned by cargo ships is up to 2,000 times higher than that used in motor vehicles.
A spokeswoman for the Environmental Protection Department confirmed that military vessels are exempted in the draft legislation, in accordance with "international practice and the actual situation in Hong Kong".
But she said: "We will consider the relevant exemptions, including warships and other vessels for military service."
The draft legislation, which will be tabled at the Legislative Council within the year, will require operators of all ocean-going vessels to switch to a diesel fuel with not more than 0.1 per cent sulphur content, from sulphur levels of 2.8 to 3.5 per cent.
Roughly 20 to 30 warships sail into Hong Kong waters each year, the Marine Department says.
Simon Ng Ka-wing, head of transport and sustainability research at think tank Civic Exchange, said an exemption for warships was to be expected.
But he questioned why no alternatives for controlling emissions of warships berthed at Central had been discussed.
"It's too late to argue whether the dock should be used for military use. The important thing is to look at how to mitigate the negative impacts," Ng said, adding that offering on-shore power was the best alternative.
He said shore power systems had actually been invented for military use as navy ships would spend longer at berth than civilian or merchant vessels.
Shore power shifts power generation from a ship's engine to an alternative shore-based electricity supply. Ng said the government needed to get in line with international practice and provide more shore power supply at docks for all ships.
The Development Bureau, which is in charge of works and rezoning, declined to say whether shore power would be provided at the berth.
Despite thousands of letters of objection, the government secured approval from the Town Planning Board in February to rezone the dock area of 0.3 hectares from open space to military use, ending a year-long debate. The government said the land had to go to the military under a pre-handover Sino-British deal, but opponents fear a promise to open the area to the public when not in use will not be met.
Society for Protection of the Harbour adviser Paul Zimmerman said it was unlikely shore power would be provided as the facility only contained four simple structures. He said it was "embarrassing" that the government did not consider the potential impact on public health.
The People's Liberation Army Hong Kong garrison did not respond to a request for comment.