Atlas Copco's new and unique dust suppression agent system is an important environmental breakthrough and a landmark in drilling techniques.

The microscopic particles of stone dust created by drilling in rock such as quartz can be so minute that they remain floating in the air at the site and carry to other areas. And it is well-known that constant exposure to fine dust over a lengthy period can lead to the onset of respiratory diseases, such as silicosis.

Efforts to solve the problem have been hampered in the past by the fact that surface tension in the drill dust repels water - making it difficult to bind the particles together so they can be controlled more easily. However, tests with an Atlas Copco ROC D7 crawler rig equipped with the new system have achieved a breakthrough.

Topping up the tank with water and foam to feed the dust suppression system.

A foaming agent is added to a mixture of water and air which is injected into the hole as the dust is being created by drilling. The mixture successfully binds together the dust particles into larger units which cannot float in the air and are rendered harmless by being effectively "grounded".

Atlas Copco's involvement in the dust suppression success story started in 1997, when the company and Skanska Norrland co-operated on a drilling contract for Banverket, the Swedish railway authority. The worksite, at Näsmoarna, Ragunda, was very close to a housing development and the local environment authority specified that the drill dust must be taken care of before blasting began.

A liquid container was mounted on an Atlas Copco ROC 642 HC-01 crawler rig, together with an air-driven drum pump. In the dust separator's outlet, water sprinklers were mounted. The water was mixed with foaming agent and, through valves and a constricted pipe, the liquid was dosed partly into the flushing air, which blows the hole clean, and partly into the dust outlet on the dust separator.

A handful of dust, ejected from the system after the particels have been bound together and rendered harmless.

Their reaction was extremely positive - but there were some reservations about whether the system would function during winter time. The rig operator, who was extremely satisfied with the way the system worked, said that refilling it with water would present the biggest drawback.

Problem solved

But this problem has now also been solved. A thermostat-regulated diesel heater with an output of 5 kW has been mounted on the rig, together with a circulation pump and a surge tank. For water refills, an electric pump was mounted and - to prevent freezing in the nozzle and hoses during long waiting periods - a mist lubricator was added to the equipment.

For manoeouvrability, magnetic valves regulated by a switch on the drill rig's control panel were mounted. During tests extremely good results were obtained and measurable values were far below the the specified danger level.

In the autumn of 1998, the testing equipment was moved over to a ROC 642 HP-01, owned by Johnny's Sprängteknik AB, to continue testing in winter.

The dust binding equipment operated well in the winter months, with water and fuel refilling being carried out simultaneously. Fuel consumption of the diesel heater is between 4 and 6 litres per day, depending on the outside temperature.


Sensitive environments

The foaming agent, an environmentally approved, totally vegetable-based product with a combination of tenside additives, can be used in very sensitive environments. To prevent freezing in winter and when drilling is not under way for long periods - the system works best in mild rather than severe winters - an environmentally approved air-tool oil is used.

When drilling 76 mm diameter holes with a normal amount of fine drill dust, around half a litre of water/foam is used per drill metre. If the fine dust increases, then the amount of water/foam must also increase. When the amount of dust depends on the sharpness of the bit, the setting for rotation, the feed force etc., adjustments should be made to achieve optimal total costs.

Consumption is also related to the hole diameter, as the amount of drill dust to be bound is a deciding factor in the amount of water/foam required.

The additional costs of drilling 76 mm-diameter holes in winter, excluding diesel for warming up, is less than SEK 0.5 per drill metre.

Project benefits

If it is permitted to leave bound drill dust on the site, a saving of nearly two tonnes is achieved in the weight that is handled or carried per shift, based on 76 mm- diameter holes, 200 drill metres and half a litre of water/foam per drillmetre.

The benefits of the project so far include: Breathable quartz particles reduced by half; total dust reduced by 90%; no fine dust is left swirling around the workplace; bound drill dust can often be left at the worksite, reducing total costs and increasing safety; less wear on drilling equipment - and a better environment for personnel and local residents.

Dust-binding equipment from Atlas Copco is currently being used on a Swedish Rail expansion project at Årsta, south of Stockholm, and Sonny's Mark & Anläggning is carrying out drill and blast operations.

Sonny Karlsson is using Atlas Copco's dust agent suppression system in his company's drill and blast operations at a rail project where cables for the trains are extremely sensitive to dust. He says: "We were very happy to accept the challenge."

Sonny Karlsson says: "Using the equipment frees us from environmental concerns - and it is very important that our drillers should have the best working environment possible."

The dust suppression system is currently available in Sweden, but is not yet being marketed internationally.