Section 690-239 - Control of coal dust and rock dusting(a) Method of removal.--(1) Dangerous accumulations of fine, dry coal dust shall be removed from a mine or neutralized by the application of rock dust, and all dry and dusty operating sections and haulageways and the back entries for at least 1,000 feet outby the first active working place in each operating section shall be kept watered down, rock dusted or dust allayed by such other methods as may be approved by the department.(2) A mine or location in a mine that is too wet or too high in incombustible content to initiate or propagate a coal dust ignition need not be rock dusted during the time any of those conditions prevail.(3) Coal dust and other dust in suspension in unusual quantities shall be allayed by sprinkling or other dust allaying or collecting devices.(b) Specifications.--(1) In a dry and dusty mine or section thereof, rock dust shall be applied and maintained upon the roof, floor and sides of all operating sections, haulageways and parallel entries connected thereto by open crosscuts. Back entries shall be rock dusted for at least 1,000 feet out by the junction with the first active working place.(2) Rock dust shall be so applied to include the last open crosscut of rooms and entries and to within 40 feet of the faces. In mines where mining is done by continuous-type mining machinery, the distances from the face to which rock dust shall be applied shall be the mining distance for one shift if: (i) The active working place shall be kept from damp to wet.(ii) After coal production on any shifts has ceased, an application of rock dust shall be made in the exposed area to within 40 feet of the face before additional mining is performed in the area.(3) Rock dust shall be maintained in such quantity that the incombustible content of the mine dust shall not be less than 65%.(c) Composition of rock dust.--Rock dust shall not contain more than 5% by volume of quartz or free silica particles and shall be pulverized so that 100% will pass through a 20-mesh screen and 70% or more will pass through a 200-mesh screen.2008, July 7, P.L. 654, No. 55, §239, effective in 180 days [ 1/5/2009].