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| Electric Blasting—Surface and Underground | 57.6400 – 57.6407 | |||||||||||||||||||||||||
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50 FR 4082, Jan. 29, 1985, unless otherwise noted.
61 FR 36801, July 12, 1996, unless otherwise noted.
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Subscribe to: 30 CFR Part 57 Subpart E - Electric Blasting—Surface and Underground
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All electric detonators to be fired in a round shall be from the same manufacturer and shall have similar electrical firing characteristics.
Except during testing—
(a) Electric detonators shall be kept shunted until connected to the blasting line or wired into a blasting round;
(b) Wired rounds shall be kept shunted until connected to the blasting line; and
(c) Blasting lines shall be kept shunted until immediately before blasting.
Electrical distribution circuits within 50 feet of electric detonators at the blast site shall be deenergized. Such circuits need not be deenergized between 25 to 50 feet of the electric detonators if stray current tests, conducted as frequently as necessary, indicate a maximum stray current of less than 0.05 ampere through a 1-ohm resistor as measured at the blast site.
(a) If electric blasting includes the use of branch circuits, each branch shall be equipped with a safety switch or equivalent method to isolate the circuits to be used.
(b) At least one safety switch or equivalent method of protection shall be located outside the blast area and shall be in the open position until persons are withdrawn.
(a) Switches used to connect the power source to a blasting circuit shall be locked in the open position except when closed to fire the blast.
(b) Lead wires shall not be connected to the blasting switch until the shot is ready to be fired.
(a) Power sources shall be capable of delivering sufficient current to energize all electric detonators to be fired with the type of circuits used. Storage or dry cell batteries are not permitted as power sources.
(b) Blasting machines shall be tested, repaired, and maintained in accordance with manufacturer's instructions.
(c) Only the blaster shall have the key or other control to an electrical firing device.
If any part of a blast is connected in parallel and is to be initiated from powerlines or lighting circuits, the time of current flow shall be limited to a maximum of 25 milliseconds. This can be accomplished by incorporating an arcing control device in the blasting circuit or by interrupting the circuit with an explosive device attached to one or both lead lines and initiated by a 25-millisecond delay electric detonator.
A blasting galvanometer or other instrument designed for testing blasting circuits shall be used to test the following:
(a) In surface operations—
(1) Continuity of each electric detonator in the blasthole prior to stemming and connection to the blasting line;
(2) Resistance of individual series or the resistance of multiple balanced series to be connected in parallel prior to their connection to the blasting line;
(3) Continuity of blasting lines prior to the connection of electric or electronic detonator series; and
(4) Total blasting circuit resistance prior to connection to the power source.
(b) In underground operations—
(1) Continuity of each electric detonator series; and
(2) Continuity of blasting lines prior to the connection of electric or electronic detonators.
[61 FR 36801, July 12, 1996, as amended at 85 FR 2027, Jan. 14, 2020]