MSHA Explosives and Blasting 2 — Questions and Answers
Question 1: What is 'flyrock' in the context of surface mine blasting, and what is the primary MSHA concern?
- A type of explosive used in quarries
- Rock propelled beyond the intended blast area, posing a hazard to workers and the public (Correct answer)
- A blasting technique used to break large boulders
- The fine dust generated after a blast detonates
Correct answer: Rock propelled beyond the intended blast area, posing a hazard to workers and the public
Flyrock refers to rock fragments thrown beyond the designated blast zone, which is a significant hazard that can injure workers, bystanders, and damage property.
Question 2: According to MSHA regulations, the magazine used to store explosives at a mine must be:
- Located within 100 feet of the active mining area for quick access
- Located a safe distance from roads, occupied buildings, and other magazines per MSHA tables (Correct answer)
- Constructed of metal to prevent theft
- Above ground only, even at underground mines
Correct answer: Located a safe distance from roads, occupied buildings, and other magazines per MSHA tables
MSHA regulations specify minimum separation distances from magazines to roads, buildings, and other magazines based on the quantity of explosives stored, as detailed in published distance tables.
Question 3: What is a 'bootleg' in blasting terminology, and why is it dangerous?
- An illegally obtained explosive
- An unbroken portion of a borehole remaining after a blast that may contain undetonated explosives (Correct answer)
- A type of fuse used in underground blasting
- Explosive material left out of an approved magazine overnight
Correct answer: An unbroken portion of a borehole remaining after a blast that may contain undetonated explosives
A bootleg is the remaining portion of a drill hole after a blast, and it is dangerous because it may contain unexploded explosive material that could detonate if disturbed during subsequent drilling.
Question 4: Under MSHA standards, electric blasting circuits must be tested before firing using:
- A standard multimeter set to the highest voltage range
- A blasting galvanometer or approved circuit tester designed for explosives use (Correct answer)
- A 9-volt battery to check continuity
- Any available electrical testing device on site
Correct answer: A blasting galvanometer or approved circuit tester designed for explosives use
Only a blasting galvanometer or an approved, low-current circuit tester designed specifically for explosives use may be used, as other devices can deliver enough current to accidentally detonate electric blasting caps.
Question 5: What is 'sympathetic detonation' in the context of explosives storage?
- A blasting technique that uses multiple delay detonators
- The accidental detonation of an explosive charge caused by the shock wave of a nearby explosion (Correct answer)
- A method of disposing of old or deteriorated explosives
- When a blaster voluntarily detonates a charge to relieve pressure
Correct answer: The accidental detonation of an explosive charge caused by the shock wave of a nearby explosion
Sympathetic detonation occurs when the shock wave from one explosion is strong enough to set off nearby explosive charges, which is why MSHA requires minimum separation distances between magazines.
Question 6: According to MSHA, what action must be taken with deteriorated or damaged explosives?
- They may be used if the damage is minor
- They must be disposed of according to manufacturer instructions and applicable regulations (Correct answer)
- They should be returned to the main magazine for later inspection
- They can be combined with fresh explosives to boost effectiveness
Correct answer: They must be disposed of according to manufacturer instructions and applicable regulations
Deteriorated or damaged explosives are unpredictable and must be disposed of safely according to manufacturer instructions and MSHA regulations, never used or stored with good product.
Question 7: What is 'stemming' in a blasting operation, and what material does MSHA recommend?
- A method of connecting detonator wires
- An inert material placed on top of the explosive in a borehole to confine the blast energy (Correct answer)
- The process of drilling the borehole before loading
- A type of delay element used in millisecond detonators
Correct answer: An inert material placed on top of the explosive in a borehole to confine the blast energy
Stemming is the inert material (typically drill cuttings or crushed stone) placed above the explosive charge in a borehole to confine blast energy into the rock, improving fragmentation and reducing flyrock.
MSHA Explosives and Blasting 2
What is 'flyrock' in the context of surface mine blasting, and what is the primary MSHA concern?