Electric blasting initiation rules

Under 1926.906(a) electric blasting caps must not be used where external sources of electricity make their use dangerous; blasting cap leg wires must be kept short-circuited (shunted) until they are put into the firing circuit. See 1926.906(a).

• If you can detect or reasonably suspect stray or extraneous currents (for example, nearby powerlines, induced currents from heavy equipment, or stray grounding paths), do not use electric caps until the hazard is removed or controlled.
• Keep cap leg wires shunted/shorted until the moment they are connected for firing to prevent accidental initiation.

Under 1926.906(b) the blaster must conduct a thorough survey for extraneous currents and eliminate all dangerous currents before any holes are loaded. See 1926.906(b).

• The survey should include checking for nearby powerlines, electrical equipment, stray grounding paths, and induced voltages.
• If any dangerous current is found, stop and correct it (de-energize, isolate, or use a nonelectric firing system) before loading holes.

Under 1926.906(c) no; all caps used in any single blast must be the same style or function and from the same manufacturer. See 1926.906(c).

• Mixing styles or manufacturers can change firing characteristics and create unreliable initiation or unsafe delays; always match caps exactly for a single blast.

Under 1926.906(d) electric blasting must use blasting circuits or power circuits according to the electric blasting cap manufacturer's recommendations or the directions of an approved contractor or their designated representative. See 1926.906(d).

• Always review and follow the manufacturer's firing diagrams and minimum current/voltage specifications.
• If using a contractor's system, get written or clearly documented procedures from their authorized representative.

Under 1926.906(e) you must ensure that the firing system can deliver the quantity of current called for by the manufacturer's recommendations before firing. See 1926.906(e).

• Verify blasting machine capacity and condition (see 1926.906(m)) and that the number of caps does not exceed rated limits (1926.906(o)).
• Test the system (with proper shorted leads and safe procedures) to confirm it will deliver the required current to all caps.

Under 1926.906(f) and 1926.906(g) connecting wires, lead wires, and bus wires must be insulated, single solid wires with sufficient current-carrying capacity. See 1926.906(f) and 1926.906(g).

• Avoid stranded or lightly insulated conductors that could break, expose conductors, or reduce current capacity.
• Select wire gauge based on the blasting machine and total circuit load to meet manufacturer requirements.

Under 1926.906(h) the insulation on all firing lines must be adequate and in good condition. See 1926.906(h).

• Inspect firing lines for nicks, cuts, exposed conductors, or rodent damage before use.
• Replace or repair any damaged insulation; do not tape over serious damage—use proper replacement wire.

Under 1926.906(i) no; a power circuit used for firing electric blasting caps must not be grounded. See 1926.906(i).

• Grounding could create a path for stray currents or accidental initiation; keep the firing circuit isolated and ungrounded unless the manufacturer's instructions specifically require an alternative.

Under 1926.906(j) and 1926.906(l) in underground operations a safety switch must be placed in the permanent firing line at intervals, be lockable only in the "Off" position, have a short-circuiting arrangement to the cap circuit, and be kept locked in the "Off" position except when firing. See 1926.906(j) and 1926.906(l).

• Keys to these safety switches must be controlled by the blaster (see 1926.906(m) and following text about keys).
• The short-circuiting arrangement protects against accidental energization while personnel are working on lines.

Under 1926.906(k) a "lightning" gap of at least 5 feet is required in the firing system ahead of the main firing switch in underground operations, between that switch and the power source; it must be bridged with a flexible jumper cord just before firing. See 1926.906(k).

• The gap reduces the chance that lightning or a power surge from the source will reach the firing circuit.
• Only place the jumper across the gap moments before firing and remove it immediately after firing as part of safe procedures.

Under 1926.906(m) blasting machines must be kept in good condition and tested periodically to ensure they can deliver power at their rated capacity. See 1926.906(m).

• Establish a routine inspection and maintenance schedule and document tests of output capacity.
• Remove defective machines from service until repaired and retested.

Under 1926.906(n) connections to blasting machines must be made as recommended by the electric blasting cap manufacturer, and under 1926.906(o) the number of caps connected to a blasting machine must not exceed its rated capacity; series circuits in primary blasting must not contain more caps than the cap manufacturer's limits. See 1926.906(n) and 1926.906(o).

• Verify both the blasting machine rating and the cap manufacturer's series limits before connecting.
• Never exceed machine or cap manufacturer specifications to avoid misfires or insufficient current.

Under 1926.906(p) the blaster must be in charge of the blasting machines, and no other person is permitted to connect the leading wires to the machine. See 1926.906(p).

• This ensures a single qualified person controls machine connections and firing authority.
• Keep clear written or procedural authority designating the blaster and prohibit unauthorized connections.

Under 1926.906(q) blasters testing circuits to charged holes must use only blasting galvanometers or other instruments specifically designed for that purpose. See 1926.906(q).

• Do not use improvised or general-purpose meters that are not designed for blasting circuit testing, as they may not be safe or provide correct readings.
• Use properly calibrated and maintained galvanometers and follow manufacturer instructions.

Under 1926.906(r) you must keep total wire lengths short enough so they cannot reach live powerlines, or securely anchor the wires to the ground to prevent them from being thrown over live powerlines. See 1926.906(r).

• Plan wire routing and anchoring before loading holes; factor in blast force and direction.
• If you cannot prevent the risk, use a nonelectric firing system as required by 1926.906(s)-following text.

Under 1926.906(s) only the person who makes the leading wire connections may fire the shot, and all connections must be made from the bore hole back to the source of firing current with leading wires remaining shorted until they are connected to the blasting machine or source just before firing. See 1926.906(s).

• This rule prevents confusion and accidental firing by limiting firing authority to the blaster who prepared the circuit.
• Keep leading wires shunted until the blaster is at the firing point and ready to fire.

Under 1926.906(t) after firing an electric blast from a blasting machine the leading wires must be immediately disconnected from the machine and short-circuited. See 1926.906(t).

• This prevents stray voltages or accidental energizing of lines after the shot.
• Ensure all personnel know the post-firing procedures and verify disconnection and shorting before returning to the blast area.

Under the design requirement in 1926.906 the keys to firing switches shall be entrusted only to the blaster so that the blaster controls access to the firing switch and ensures the firing lines are short-circuited when the switch is in "Off." See 1926.906(l).

• Restricting keys prevents unauthorized persons from enabling the firing circuit and protects workers during line connection or maintenance.
• Combine key control with locking switches in the "Off" position and short-circuiting arrangements for safe operations.

Under 1926.906(o) yes; in primary blasting a series circuit shall contain no more caps than the limits recommended by the electric blasting cap manufacturer, and the total number of caps on a blasting machine must not exceed its rated capacity. See 1926.906(o).

• Check the cap manufacturer's series-cap limits and the blasting machine rating before assembling series circuits.
• Exceeding these limits can result in insufficient current, misfires, or unsafe detonations.

Under the text following 1926.906(r) and as reinforced by 1926.906(s), if you cannot keep wires short enough or secure them to prevent contact with powerlines, you must use a nonelectric firing system. See 1926.906(r) and the text following it.

• Nonelectric systems (e.g., shock tube or detonation cord-based systems) eliminate the hazard of stray electrical currents triggering caps.
• Evaluate site conditions during planning and choose firing methods that eliminate electrical hazards.

Under 1926.906(p) no—only the blaster shall be in charge of the blasting machines and no other person may connect the leading wires to the machine; 1926.906(m) requires machines to be tested and in good condition under the blaster's oversight. See 1926.906(p) and 1926.906(m).

• This centralizes responsibility and reduces the risk of improper connections or unauthorized firing.
• Establish procedures that identify the blaster and prohibit others from making connections.

Under 1926.906(q) testing circuits to charged holes must be done with blasting galvanometers or instruments specifically designed for that purpose because they are calibrated and constructed to safely measure low currents and continuity in blasting circuits. See 1926.906(q).

• General-purpose voltmeters or ammeters may not provide correct readings, can introduce unsafe currents, or be unsafe to use in blasting circuits.
• Always use instruments intended for blasting and follow manufacturer and training instructions.

Under 1926.906(k) and 1926.906(l) you must maintain a lightning gap of at least 5 feet ahead of the main firing switch and lock the firing switch in the "Off" position until firing; the gap is bridged with a flexible jumper cord only just before firing. See 1926.906(k) and 1926.906(l).

• Keep the gap open while personnel are working on or near the lines; place the jumper across the gap only when everyone is clear and the blaster is ready to fire.
• Remove the jumper and reestablish the gap immediately after firing.

Under 1926.906(s) in electrical firing only the man who makes the leading wire connections shall fire the shot, and all connections must be made from the bore hole back to the source while the leading wires remain shorted until the moment of connection; this reduces the risk of confusion and accidental firing. See 1926.906(s).

• Limiting firing authority to the person who wired the circuit ensures they know the circuit status and reduces communication errors.
• Combine this rule with key control over switches and short-circuiting safety practices for safe operations.