Home > Addressing a Noxious issue: Making blasting safer

Addressing a Noxious issue: Making blasting safer

Editorial
article image NOx is often formed during wet blasts, creating a deadly gas.

In March 2011, a number of Queensland coal miners were hospitalised following exposure to nitrogen dioxide after blasting went wrong on site.

Soon after this, more open cut miners were exposed to the deadly fumes after blasting.

These two similar incidents back to back caused a shake up of the Queensland mining industry and brought about the introduction of new blasting guidelines to minimise the dangers of nitrogen dioxide, known as NO2 or NOx, forming after blasting.

This gas, often created during shot firing, can turn into nitric acid in a person's lungs once inhaled.

While steps are taken to avoid post blast fume events, the formation of this potentially deadly gas is always a possibility.

So what exactly causes this, and what is being done to prevent it?

Almost without exception, blasting in Australia uses a mixture of ammonium nitrate and fuel oil or ANFO.

However the blasting of ANFO explosives can cause those familiar orange post-blast clouds of nitrogen dioxide that rise into the air.

These clouds of NOx can creep across the mine's boundaries into the surrounding area, causing serious problems for local residents near the mines, particularly in regions such as the Bowen Basin or Hunter Valley where mines are located close to communities.

Realising this ongoing problem is a serious burden on a mining industry which has failed to address the root problem of post blast fumes, explosives manufacturer Dyno Nobel approached investigators and the University of Newcastle to examine how blasting can be better.

They focused on the effect of chemical factors and the mechanisms of how different additives control nitrogen dioxide creation during blasting. 

The group's aim is to develop a new generation of low fume products for the industry.

Speaking to Newcastle University professor Bogdan Dlugogorski, he told Ferret they are investigating the "fundamentals of the NOx problem in blasting.

"We are asking why nitrogen dioxide is produced in open cut blasting," he said. 

Dlugogriski explained that while a number of solutions have been implemented for open cut blasting, they do not really address the issue of why NOx forms in the first place. 

Most solutions relate to safe blasting radii, measuring the range of exposure, and a number of retroactive measures such as monitoring levels of the gas following blasting.

Current World Health Organisation guides lines for NOx are a one hour level of 200µg m3 (approximately 200 parts per billion), and an annual average of 40µg m3.

However, typical concentrations of NOx in post blast clouds can measure anywhere between 5.6 to 580 parts per million, exceeding the safe limits by around 30 to 3000 times. 

This is clearly far too high.

Dlugogorski said their research over the next three years is trying to understand what works, why, and what is the range of these potential solutions in the long term.

"Our objective is to find practical solutions to decrease the frequency and magnitude of the formation of blast NOx during firing, leading to the development of new products and new blasting guidelines."

He said the group at Newcastle University has previously carried out research on the same NOx problem in underground blasting, and is planning to approach fume events in open cut mines in the same way.


 
"We started by understanding how it formed and the mechanisms that caused it, developed different gassing chemistry so that the explosives operated at lower temperatures and created chemical traps to remove the nitrogen dioxide," Dlugoroski told Ferret

The group has a number of main aims; firstly to gain an insight into the formation of nitrogen oxide in-situ blasting (i.e. in a borehole) as a consequence of low blasting temperatures, or fuel lean or oxidiser rich conditions, where the objective is test the theory that it forms either under low temperature or fuel deficient conditions. 

After this it will investigate the reduction of nitrogen oxide in-situ due to extra fuel in the explosives or higher temperatures.

From this, the research group will then use modelling to determine exactly how NOx forms under different field conditions, after which it will look at ways to mitigate the emissions by either changing the product or completely changing the way blasting it carried out.

This modelling is a major part of development, as although the factors which affect post blast nitrogen oxide formation are known, the effects have never really been quantified before.

It is this gap in knowledge that has stymied the ability to predict nitrogen oxide, and subsequent NOx formation, from the surrounding rocks and explosives mixture. According to Dlugogorski, the theoretical, practical and quantative knowledge created by the project's findings will be published openly, for overall progress in the field.

While this project is still in its infancy, it has received a major boost.

The University of Newcastle has been granted funding to develop this new mining technology.

The Linkage Program grant from the Australian Research Council will provide half a million dollars for research and development.

Acting deputy vice-chancellor of the University, professor Scott Homes, said these projects will build on the University's track record of research.

"These latest projects will ensure that we remain at the forefront of research and development of technology that addresses the needs of industry and boosts sustainability and efficiency," Holmes said.

This funding follows the creation of the Newcastle Institute for Energy and Resources (NIER), which brings together the University's energy and resources researchers.

Dlugogorski hopes the research uncovers a number of practical solutions for NOx and moves the blasting industry forwards.

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