Published in Australian Longwall Magazine
The Silent Seal product produced by Fomo Products has become widely used in Australia since gaining approvals from the New South Wales Department of Mineral Resources. (In Queensland use of the product is subject to mine manager risk assessment).
Silent Seal is sold in Australia through Ground Consolidation, best known as a supplier of cements and cavity filling material and as a PUR installation contractor.
Silent Seal is used to seal areas on and around a ventilation stopping, mainly where the stopping meets the roof and floor, and connecting areas such as ribs. These foams have the ability to expand and create airtight seals on and around mine stoppings, reducing air leakage to a miniscule amount.
While ventilation sealing remains the major application for Silent Seal, according to Ground Consolidation managing director Ian Yates, the foam is also being used in Australian mines to expedite cavity-filling work on longwalls and to plug off cable bolts.
For example, where shuttering is to be built above a longwall face, traditionally gaps are plugged with cotton waste. Yates said Silent Seal was a more effective way of plugging gaps. It exhibits high tensile strength and adheres to a variety of substrates to such an extent that it will tear cohesively, within itself, as opposed to tearing adhesively (away from the substrate).
Similarly with cable-bolt plugging, rags are often used to pack the bottom of the hole in order to prevent the grout from falling out, which is not always effective. Silent Seal foam offers a fast, effective alternative. Yates said a single component application in a smaller canister was currently being approved for this type of application.
At first consideration of representing the Fomo products in Australia, Yates was initially very sceptical. “Over the years there have been many problems with products like these, particularly in the United States,” Yates said. “But I have seen the ferocious tests this product has been subjected to in South Africa and there’s nothing else like it.”
Silent Seal NA was developed to meet MSHA (Mine Safety and Health Administration) requirements in the US, which involves passing the ASTM E-162 radiant heat panel test with a flame spread of less than 25.
Silent Seal SA was designed to meet the requirements of the South African CSIR (Centre for Scientific & Industrial Research) for smouldering combustion, large-scale horizontal flame spread, large-scale vertical flame spread, and toxicity of combustion gases.
“It was an especially difficult challenge to formulate flame resistant urethane without the use of halogenated blowing agents. However, once accomplished, Silent Seal SA has become the only urethane based foam with full CSIR approval,” said Fomo technical director, Dr Tom Fishback.
“The most important property of a foam sealant, other than its ability to act as an effective air barrier, is the ability to resist fire,” said Fishback.
While there are no formal tests of the product’s efficacy in improving ventilation, Yates said there was plenty of anecdotal evidence to suggest mines which were using the foam effectively were less reliant on fans and used less power. Australia is also one of the major users of the Silent Seal products, evidence of its widespread acceptance.
Fomo offers its foam in portable kits which allow a miner to seal off the interface around a stopping in a matter of minutes and to quickly repair small breaches or cracks in stoppings.
Silent Seal-type foams can also be used for thermal insulation, as an air barrier against dust and moisture, and to reduce noise and vibration. Additional applications for Silent Seal in the mining industry include diversion and control of water run-off, sealing railroad hopper cars and spill containment.
While mine ventilation engineers have been able to improve the amount of fresh air reaching the last crosscut by over 50% in the last 50 years, there is still the potential for significant improvement, Fishback said.
