What's an exhaust stack and are they dangerous?

Smoke stacks (also called exhaust stacks, pollution stacks or ventilation stacks) have been in the news recently regarding both the WestConnex toll road and the Beaches Link. But what are they, and could they be harmful?


What's a smoke stack? What does it look like?

Here's what the NSW Chief Scientist says about smoke stacks:

Many road tunnels vent exhaust air to the atmosphere at the exit portals. However, in busier or longer tunnels (typically those longer than 2km) emissions can build up to levels where in-tunnel air quality exceeds acceptable limits. In such cases, ventilation stacks have often been used to increase the throughput of fresh air, effectively increasing the allowable vehicle capacity.

Put simply, smoke stacks are chimneys that carry polluted air from road tunnels into the outside environment. This is a photo of a smoke stack for the M5 motorway at Turrella:

Initial plans submitted for a smoke stack at Haberfield suggested it would be 26 metres high.

Will the stacks be filtered to remove toxic gases from the air?

No. As a matter of policy, no tunnel ventilation stacks are not filtered in NSW.

How have the government decided if the level of pollution from the stacks will be dangerous?

Predicted air pollution from smoke stacks and roads is measured against Australian Air Quality Standards, decided by the National Environment Protection Measure (NEPM), which was set up in the 1990s by environment ministers who formed a political agreement on air quality standards.

Australia therefore has lower air quality standards than the global standards set by the World Health Organisation. Australian standards are not always updated in line with the latest scientific research from around the world. 

How will pollution from stacks be measured? 

Air pollution is measured by Roads and Maritime Services. But monitoring the ambient air quality, as RMS has done, cannot reliably predict the size, nature and course of adverse health impacts of air from tunnels. As this report from the National Health and Medical Research Council shows, tunnel emissions are fundamentally different, both in composition and capacity to do harm, from the components of ambient air. They cannot be assessed in the same way. 

Based on their own monitoring, the government has denied there will be a ‘measurable impact’ from the stacks. But as the monitoring methods they've used to reach this conclusion aren't reliable enough, this does not demonstrate the absence of harm. 

What pollutants are they measuring?

The RMS have measured tiny air particles measuring less than 10 microns in diameter (these are called PM10 particles) and less than 2.5 microns in diameter (these are called PM 2.5).

But the air also contains another type of dangerous particle that can cause harm to health. These are extra small particles known as ultra-fine particles. Their small weight means they haven't been accurately measured, so their health impacts on the local people can't be adequately predicted.

We do know, however, that ultrafine particles can be extremely harmful, as their small size means they are easily inhaled deep into the lungs - with some even getting inside the cells of the lungs. Diesel engines used by cars today emit more ultrafine particles than ever before.

What health risks are associated with air pollution?

Polluting the air kills people much like selling them cigarettes or asbestos. The more pollutants in the air we breathe and the longer we breathe them, the greater the risks to health.

Medical research confirms that pollutants from diesel exhaust cause lung cancer, bladder cancer, heart disease, heart attacks, strokes, asthma attacks, and lung damage in children.

The experts from the International Agency for Research in Cancer of the World Health Organisation classified diesel exhaust as a Group 1A carcinogen – in the same group of cancer causing agents as arsenic and mustard gas.

What's a safe level of pollution from smoke stacks?

The latest World Health Organisation air quality guidelines state, “There is little evidence to suggest a threshold below which no adverse health effects would be anticipated",  and an international workshop of multiple pollution experts in 2009 concluded, “There are no established thresholds of exposure below which population health impacts are absent.”

In other words, there is NO level at which air pollution is completely safe, especially for more vulnerable people, children, and the elderly.

So what's the solution?

WestConnex as a project should be scrapped. It poses serious health risks, as well as inducing more cars onto the roads, increasing air pollution and contributing to global waming. It will destroy communities and wipe out much needed green spaces, without significantly decreasing travel times.

Please have your say by signing our joint submission to the government on WestConnex stage 3. 


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  • Gemma Pitcher
    published this page in News 2017-08-16 13:16:32 +1000

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