CES Assessment & Evaluation Techniques 3 — Questions and Answers
Question 1: The scaled distance formula used in blast vibration assessment relates which variables?
- Maximum charge weight per delay and distance from the blast (Correct answer)
- Total explosive weight and detonation velocity
- Hole diameter and stemming length
- Stand-off distance and airblast overpressure
Correct answer: Maximum charge weight per delay and distance from the blast
Scaled distance (SD) = Distance / √(Maximum Charge Weight Per Delay), and is the key formula used to predict and evaluate ground vibration compliance.
Question 2: Which document serves as the primary reference for evaluating structural damage risk from blasting vibrations in the United States?
- OSMRE guidelines and USBM RI 8507 (Correct answer)
- NFPA 495
- ATF Federal Explosives Law and Regulations
- OSHA 1910.109
Correct answer: OSMRE guidelines and USBM RI 8507
USBM (U.S. Bureau of Mines) Research Investigation 8507 established the scaled distance and PPV limits widely adopted by OSMRE for structural damage risk evaluation.
Question 3: In evaluating detonator performance, electric resistance testing serves what primary purpose?
- Confirming circuit continuity and identifying faulty detonators before firing (Correct answer)
- Measuring the detonator output pressure
- Verifying the no-fire current threshold
- Assessing the detonator's water resistance rating
Correct answer: Confirming circuit continuity and identifying faulty detonators before firing
Resistance testing of electric detonator circuits confirms continuity and identifies open circuits, shorts, or out-of-tolerance units before firing, preventing misfires.
Question 4: A blasting crew reports excessive flyrock during a quarry shot. Which evaluation factor should be examined FIRST?
- Stemming length and material adequacy (Correct answer)
- Powder factor relative to target rock
- Hole spacing and burden measurements
- Delay timing sequence
Correct answer: Stemming length and material adequacy
Inadequate stemming is the most common cause of flyrock, as insufficient confinement allows explosive gases to vent prematurely and propel rock fragments.
Question 5: When assessing airblast overpressure from a surface blast, the maximum acceptable level for residential structures is typically:
- 0.1 psi (pounds per square inch)
- 133 dBL (linear) (Correct answer)
- 1.0 psi
- 160 dBL
Correct answer: 133 dBL (linear)
USBM research established 133 dBL as the airblast overpressure level below which residential structural damage is unlikely, and this is the standard regulatory threshold.
Question 6: Which method is used to evaluate the critical diameter of a bulk explosive formulation?
- Conducting a series of detonations in pipes of decreasing diameter until failure (Correct answer)
- Running the card gap sensitivity test at ambient temperature
- Comparing the heat of detonation against a TNT equivalent
- Measuring the VOD at full column height
Correct answer: Conducting a series of detonations in pipes of decreasing diameter until failure
Critical diameter is determined empirically by detonating the explosive in containers of progressively smaller diameter until the detonation fails to propagate, identifying the minimum viable diameter.
Question 7: For evaluating the sympathetic detonation hazard between two explosive charges, the key parameter assessed is:
- Critical separation distance based on charge weight and explosive type (Correct answer)
- The combined net explosive weight of both charges
- The detonation velocity of the donor charge only
- The ambient temperature at the storage site
Correct answer: Critical separation distance based on charge weight and explosive type
Sympathetic detonation risk is evaluated by determining the critical separation distance—the minimum safe distance at which a donor explosion cannot initiate the acceptor.
CES Assessment & Evaluation Techniques 3
The scaled distance formula used in blast vibration assessment relates which variables?