CDS Materials & Equipment Knowledge 3 — Questions and Answers
Question 1: What equipment is used to conduct a 'structure-borne vibration' assessment during near-structure demolition blasting?
- Dosimeter
- Seismograph (Correct answer)
- Anemometer
- Photometric analyzer
Correct answer: Seismograph
A seismograph measures ground vibration velocity (in/s) to ensure blasting does not exceed damage thresholds for adjacent structures.
Question 2: Which crane attachment configuration provides the highest level of reach and precision for high-rise demolition work?
- Dragline with clamshell bucket
- Long-reach excavator with shear attachment (Correct answer)
- Crane with demolition grapple on fixed boom
- Telescoping boom crane with concrete pulverizer
Correct answer: Long-reach excavator with shear attachment
Long-reach excavators with hydraulic shear attachments can precisely cut structural steel and concrete at elevated heights while maintaining stability.
Question 3: What is the OSHA-required minimum safe standoff distance factor when using explosive demolition near occupied buildings?
- It is determined solely by the building owner
- It is calculated based on charge weight and must conform to OSHA 1926.909 and ATF requirements (Correct answer)
- A flat 500-foot exclusion zone is always required
- Only local fire marshal approval is needed
Correct answer: It is calculated based on charge weight and must conform to OSHA 1926.909 and ATF requirements
Safe standoff distances for explosive demolition are calculated using the charge weight-to-distance formula per OSHA 1926.909 and applicable ATF regulations.
Question 4: Which property makes post-tensioned concrete slabs uniquely hazardous during demolition compared to conventionally reinforced concrete?
- Post-tensioned slabs contain higher levels of lead-based paint
- Cutting tendons releases stored tensile energy that can propel debris violently (Correct answer)
- Post-tensioned concrete is more likely to contain asbestos
- The concrete mix is more alkaline and causes chemical burns
Correct answer: Cutting tendons releases stored tensile energy that can propel debris violently
Post-tensioned tendons are under high stress; cutting them releases sudden energy that can cause concrete to fracture explosively and fling debris.
Question 5: What is the primary advantage of using a wire saw for cutting thick concrete walls compared to other methods?
- It requires no water for cooling or dust suppression
- It can cut virtually unlimited thicknesses without repositioning (Correct answer)
- It is the fastest cutting method available for demolition
- It eliminates all vibration during the cutting process
Correct answer: It can cut virtually unlimited thicknesses without repositioning
Diamond wire saws can cut through sections of any thickness and are ideal for large or irregular concrete elements that exceed other saw capacities.
Question 6: In demolition, 'overburden' most accurately refers to:
- Excess concrete poured above the specified slab thickness
- Soil, debris, or non-structural material overlying a structure or foundation to be demolished (Correct answer)
- Structural loads that exceed design capacity during demolition sequencing
- Additional explosive charge used to ensure complete fragmentation
Correct answer: Soil, debris, or non-structural material overlying a structure or foundation to be demolished
Overburden refers to the earth or debris layer above the target structure, which must often be removed before demolition equipment can access the foundation.
Question 7: Which type of crane rigging hardware is specifically designed to prevent accidental unlatching when loads are lifted during demolition debris removal?
- Standard J-hook
- Shackle with a safety pin (Correct answer)
- Latch-hook
- Swivel eye bolt
Correct answer: Shackle with a safety pin
Shackles with safety pins (or screw-pin shackles with the pin moused/wired) prevent accidental opening under dynamic load conditions common in demolition lifting.
CDS Materials & Equipment Knowledge 3
What equipment is used to conduct a 'structure-borne vibration' assessment during near-structure demolition blasting?