Stemming boreholes.

§ 75.1322 Stemming boreholes. (a) Only noncombustible material shall be used for stemming boreholes. (b) Stemming materials other than water stemming bags shall be tamped to fill the entire cross sectional area of the borehole. (c) Stemming material shall contact the explosive cartridge nearest the collar of the borehole. (d) Each borehole 4 or more feet deep shall be stemmed for at least 24 inches. (e) Each borehole less than 4 feet deep shall be stemmed for at least half the depth of the borehole. (f) When blasting off the solid in bituminous and lignite mines, only pliable clay dummies shall be used for stemming. (g) The diameter of a water stemming bag shall be within 1/4 of an inch of the diameter of the drill bit used to drill the borehole. (h) Water stemming bags shall be constructed of tear-resistant and flame-resistant material and be capable of withstanding a 3-foot drop when filled without rupturing or developing leaks.