CES CES Blasting Operations & Techniques 1 — Questions and Answers
Question 1: What is the primary purpose of a pre-blast inspection in surface blasting operations?
- To identify nearby structures, utilities, and conditions that could be affected by the blast (Correct answer)
- To calculate the cost of the blasting operation
- To determine the color-coding of detonators
- To verify the blasting crew's lunch schedule
Correct answer: To identify nearby structures, utilities, and conditions that could be affected by the blast
A pre-blast inspection identifies structures, utilities, and environmental conditions that may be affected by ground vibration, airblast, or flyrock.
Question 2: In bench blasting, what does the term 'burden' refer to?
- The weight of explosives loaded per hole
- The perpendicular distance from the free face to the front row of blast holes (Correct answer)
- The total cost of explosives used
- The delay interval between rows
Correct answer: The perpendicular distance from the free face to the front row of blast holes
Burden is the perpendicular distance from the front row of blast holes to the nearest free face, and it directly influences fragmentation and ground movement.
Question 3: Which delay timing system minimizes flyrock and overbreak by allowing sequential detonation of blast holes?
- Instantaneous initiation of all holes simultaneously
- Electric millisecond delay detonators or electronic detonators with programmed delays (Correct answer)
- Detonating cord trunk lines with no delays
- Manual fuse ignition in no particular order
Correct answer: Electric millisecond delay detonators or electronic detonators with programmed delays
Millisecond delay or electronic detonators allow sequential detonation that controls rock movement, reduces overbreak, and minimizes flyrock.
Question 4: What is the recommended minimum stemming length above explosive column in a blast hole?
- Equal to or greater than the burden distance (Correct answer)
- At least 10 feet regardless of hole diameter
- One-half the drill depth
- Stemming length is optional and varies by preference
Correct answer: Equal to or greater than the burden distance
Industry practice and many regulations require stemming length to be at least equal to the burden to contain gases, reduce airblast, and improve fragmentation.
Question 5: What does the term 'specific charge' (or powder factor) mean in blasting operations?
- The sensitivity rating of the explosive
- The weight of explosive used per unit volume or ton of rock broken (Correct answer)
- The charge per detonator used
- The cost per pound of explosive
Correct answer: The weight of explosive used per unit volume or ton of rock broken
Powder factor (specific charge) is expressed as pounds of explosive per ton or cubic yard of rock and is used to design and evaluate blast efficiency.
Question 6: In underground blasting, what is the function of a 'cut' in a round?
- To provide a free face and void space so subsequent holes can break rock effectively (Correct answer)
- To mark the boundary of the tunnel perimeter
- To designate holes loaded with detonating cord only
- To indicate the location of the blasting machine
Correct answer: To provide a free face and void space so subsequent holes can break rock effectively
The cut (burn cut, wedge cut, etc.) creates the initial void and free face in solid rock so that subsequent blast holes have room to break and displace material.
CES CES Blasting Operations & Techniques 1
What is the primary purpose of a pre-blast inspection in surface blasting operations?