DOMAIN 1: UNIT 3: Excavation Hazards Flashcards
What is the primary purpose of air monitoring in underground excavations?
A) To maintain proper lighting levels
B) To detect hazardous contaminants
C) To reduce worker fatigue
D) To communicate between underground and above-ground personnel
Answer: B) To detect hazardous contaminants
Explanation: Air monitoring is crucial for identifying hazardous contaminants that may not be detectable without instruments, ensuring worker safety.
At what gas concentration level should ventilation be increased to reduce hazardous gases below the threshold?
A) 2% of the Lower Explosive Limit (LEL)
B) 5% of the Lower Explosive Limit (LEL)
C) 8% of the Lower Explosive Limit (LEL)
D) 10% of the Lower Explosive Limit (LEL)
Answer: B) 5% of the Lower Explosive Limit (LEL)
Explanation: Ventilation must be increased when gas levels reach 5% of the LEL to prevent hazardous conditions.
When is it mandatory to suspend work involving hot work like welding in underground environments?
A) When gas concentration reaches 5% of the LEL
B) When gas concentration reaches 8% of the LEL
C) When gas concentration reaches 10% of the LEL
D) When any gas concentration is detected
Answer: C) When gas concentration reaches 10% of the LEL
Explanation: Work must be stopped if gas levels reach 10% of the LEL to prevent ignition and explosion risks.
According to OSHA Standard 1926.800, what is the minimum ventilation rate required in underground worksites?
A) 50 cubic feet of fresh air per minute per worker
B) 100 cubic feet of fresh air per minute per worker
C) 150 cubic feet of fresh air per minute per worker
D) 200 cubic feet of fresh air per minute per worker
Answer: D) 200 cubic feet of fresh air per minute per worker
Explanation: OSHA mandates this ventilation rate to maintain safe air quality underground.
Which of the following signs indicates distressed soil at an excavation site?
A) Increased air pressure
B) Clear, stable trench walls
C) Spalling or small chips breaking off
D) Decreased water levels
Answer: C) Spalling or small chips breaking off
Explanation: Spalling indicates soil instability and increased risk of collapse.
In trench excavations, what is the maximum allowable slope for a trench dug in ‘Type C’ soil (sand)?
A) 34 degrees
B) 45 degrees
C) 53 degrees
D) 90 degrees
Answer: A) 34 degrees
Explanation: Type C soil requires a maximum slope of 34 degrees to prevent collapse.
How often should excavation sites be inspected for safety and hazard assessment?
A) Weekly
B) Daily and whenever conditions change
C) Monthly
D) Only after severe weather
Answer: B) Daily and whenever conditions change
Explanation: Frequent inspections ensure safety especially when conditions shift.
What is the required response time for rescue teams when there are 25 or more workers underground?
A) 10 minutes
B) 20 minutes
C) 30 minutes
D) 60 minutes
Answer: C) 30 minutes
Explanation: OSHA requires a response time of 30 minutes for underground rescue when 25 or more workers are present.
What should be done if a utility company does not respond within 24 hours of notification before excavation?
A) Abandon the excavation project
B) Proceed cautiously using detection equipment
C) Ignore the utility lines and start excavation
D) File a complaint with OSHA
Answer: B) Proceed cautiously using detection equipment
Explanation: If no response is received proceed cautiously while detecting underground utilities to prevent accidents.
What is the main function of trench shields (‘trench boxes’)?
A) To provide ventilation in deep trenches
B) To stabilize soil and prevent collapse
C) To maintain lighting in underground work
D) To monitor air quality
Answer: B) To stabilize soil and prevent collapse
Explanation: Trench boxes protect workers by holding back soil and preventing cave-ins.
