“Site-specific safe work procedures need to be developed in consultation with all relevant persons,” Regan said.

“Work needs to be planned to identify and control risks. It is possible to hose down pipes, ventilation ducting or belt structure prior to removal and transport.

“If eliminating the risk is not possible then the remaining hierarchy of controls needs to be applied. This can include improved ventilation, dust suppression, maintaining equipment and closer supervision.

“Deputies are not immune from a failed result and are expected to lead by example and implement the control strategies for each activity. Finally, and not as a substitute for the other controls, personal protective equipment can be worn.”

The problem is also being taken seriously in Queensland by its Mines Inspectorate in the Department of Employment, Economic Development and Innovation.

Queensland’s coal industry has adopted exposure limits of 10mg per cubic metre of inhalable dust, the same as used in NSW coal mines. This limit is considered best practice and is in line with the national exposure standard for inhalable dust.

Some underground coal mines in Queensland monitor exposure to inhalable coal dust. In general the results measured in Queensland’s underground coal mines are less than 50% of the NSW limit and even lower in the open cut coal mines.

The Mines Inspectorate’s Health Surveillance Unit is conducting a report into inhalable coal dust in the state’s coal mines. The report is not yet finalised but is eagerly anticipated by the industry.

The NSW Coal Services’ Standing Committee on Dust Research and Control has produced a booklet to promote a better understanding of the health effects and control of both inhalable and respirable airborne dust.

Specifically, Coal Services recommends the isolation or capture of dust sources via sealing of transfer points and crushers.

As well as ventilation of the correct quantities and at the right location, it recommends advance ventilation ducting and brattice to be standard.

Regular maintenance of dust suppression equipment is essential as is operator positioning, job rotation and automation, it says.

Control of dust levels along travelling roads needs to be vigilantly enforced and personnel should have respiratory protection by personal protective equipment.

Operating water sprays should be placed at appropriate locations and as near as possible to the point of breakage with sufficient water volumes, pressure and correct sizing of water jets and droplets, Coal Services says.

There are several products on the market that are used to suppress dust in longwall and other settings.

One is the 3M SDS2 dust suppressant, which allows water to “go further” when used according to instructions. It is ideal for construction sites, ungrassed areas, roadway dust suppression and continual longwall coal mining dust control, 3M said.

The SDS2 dust suppressant should be applied at an identical volume per square metre as water, which is recommended to not exceed 0.5 litres/sq.m per application pass.

Application frequency is then reduced as appropriate to control dust levels to site requirements.

The frequency of application will vary by site and depend on such factors as wind and humidity. A typical dilution rate of 0.2% means two 20-litre pails of SDS2 are added to 20,000 litres of water.

Lower or higher dilution rates can be applied, depending on individual circumstances, 3M says.

But some analysts say the use of fine atomising air or water sprays may not be effective when tested in longwall mining conditions.

In a paper given to the 2009 Coal Operators’ Conference at Wollongong University, Ian McDonell said there might be many other scientific reasons for lack of effectiveness of longwall dust suppression that could be based on fluid mechanics and aerodynamic principles.

“Suppression of dust by water droplets in a moving airstream requires impacts between the dust and droplets,” he said. “By impacting, the dust adheres to the droplet, falling under gravity to floor level.

“Conventional logic suggests that a higher quantity of finer water droplets will suppress the dust better. This is not often backed up by actual data, but inconsistencies in data collection may hinder the true analysis.

“Around the shearer drums, and in the outbye shearer clearer zone, turbulence is created in such magnitude so as to be a credible factor in creating these impacts. The maingate to face corner should also have a certain amount of turbulence that can be used with sprays to remove both incoming dust and dust created by the longwall from such sources as the shearer at the maingate, coal breakage on the chain, and from the movement of the shields.

“The face to tailgate corner is similar to the maingate end in this respect.”

McDonell outlined various means of enhancing inhalable dust suppression as well as their potential weaknesses.

Firstly, he recommends using a smaller size of water droplets through air and water-atomising sprays. The downside of this solution is that it leads to vastly decreased water flow rates.

Secondly, he recommends increasing the size of dust particles but ensuring there is less fracture of the coal and rock by using modified cutting picks, modified drums, lacing, flights, slower drum speeds, slower chain speeds and modified lump breaker.

This may lead to reduced shearer output and potential blockages from larger lump sizes.

He also believes that increased turbulent zones through airflow deflectors and air blowers may be effective but care needs to be taken that no damage to equipment from face spalling and impacting with the shearer and shields takes place.

Zones of turbulence are known to occur when airflow passes over an airfoil. The rear turbulence zone is much stronger than the frontal one, but due to the airstream velocity effect, more impacts are likely at the front. In a longwall environment, the majority of impacts only happen in the extremely turbulent zones around the drums and clearers.

“The balance of the face, that is from maingate to shearer, and from shearer to tailgate, and tailgate corner outbye are all zones of laminar airflow, and as such may rely more on luck for impacts rather than turbulence,” McDonell said.

“In all probability, dust suppression in these areas could only occur if additional turbulence is introduced, for example by way of deflection curtains and spray systems.”

Modified turbulent zones can also be effective if cowls are used to contain zone shrouding around the shearer and clearers.

Dust scrubbers mounted on the shearer and the use of rotary air curtain drums can also be effective but need to be weighed against the cost, McDonell said.