Design and Characterization of Canopy Air Curtain for Protecting Against Diesel Particulate Matter Exposures in Underground Mines

Blasters are one of the highest exposed work groups to diesel particulate matter (DPM) in underground metal/nonmetal mining. These workers can spend a good portion of their day under a canopy in a basket loading blastholes with explosives. Therefore, one way of potentially reducing their exposures to DPM is to place a canopy air curtain (CAC) on the basket of the ANFO loader. In the original design of the CAC on a roof bolting machine and shuttle car, a fan draws in air through a filter to capture the dust and then supplies clean air beneath the canopy where a miner is working. This paper describes the testing of a CAC that was redesigned to fit an ANFO loader and prevent exposures to DPM as well as respirable dust. Laboratory measurements demonstrated reductions of submicron particles that relate to the percent reductions of DPM. The CAC provided substantial protection of mine workers to DPM (80% reductions), from within 15.24 cm (6 inches) of the edge of the CAC using a 7.62-cm (3-inch) lip. As the mine worker approaches the edges of the CAC, the percent reduction starts to reduce to the 30–50% range. The mine worker achieves the best results when within 15.24 cm (6 inches) from the edge of the CAC. In addition, the CAC should be located such that the breathing zone of the mine worker is 25.4–50.8 cm (10–20 inches) below the CAC.

Field study results of a 3rd generation roof bolter canopy air curtain for respirable coal mine dust control

A 3rd generation roof bolter canopy air curtain (CAC) has been developed and constructed by J.H. Fletcher & Co., Inc. As with the previous generation of the CAC, this design uses the principle of providing uniform airflow across the canopy area as recommended by the National Institute for Occupational Safety and Health. The new modifications include a plenum that is constructed of a single flat aluminum plate, smaller-diameter airflow openings, and a single row of perimeter nozzles designed to prevent mine air contaminated by respirable dust from entering the CAC protection zone. Field testing was conducted on this new 3rd generation design showing reductions in coal mine respirable dust exposure for roof bolter operators. Dust control efficiencies for the CAC for the left bolter operator (intake side) ranged from approximately 26%–60%, while the efficiencies for the CAC for the right bolter operator (return side) ranged from 3% to 47%.