ESC ESC Arc Flash & PPE Selection 1 — Questions and Answers
Question 1: What causes an arc flash event?
- Overloaded neutral conductors
- An electrical arc traveling through ionized air between conductors or to ground (Correct answer)
- A ground fault in a 120V circuit
- Overheating of insulated conductors
Correct answer: An electrical arc traveling through ionized air between conductors or to ground
An arc flash occurs when an electrical arc travels through ionized air between conductors or from a conductor to ground, releasing tremendous thermal and blast energy.
Question 2: Which NFPA standard provides the requirements for arc flash hazard analysis and electrical safety in the workplace?
- NFPA 70
- NFPA 70E (Correct answer)
- NFPA 101
- NFPA 72
Correct answer: NFPA 70E
NFPA 70E, Standard for Electrical Safety in the Workplace, establishes the requirements for arc flash hazard analysis and safe work practices.
Question 3: In what units is incident energy from an arc flash measured?
- Joules per meter
- Watts per square meter
- Calories per square centimeter (cal/cm²) (Correct answer)
- BTUs per hour
Correct answer: Calories per square centimeter (cal/cm²)
Incident energy from arc flash is measured in calories per square centimeter (cal/cm²), representing the thermal energy density at a given distance from the arc.
Question 4: The arc flash boundary is defined as the distance at which incident energy equals:
- 0.5 cal/cm²
- 1.2 cal/cm² (Correct answer)
- 4 cal/cm²
- 8 cal/cm²
Correct answer: 1.2 cal/cm²
The arc flash boundary is the distance from the arc source at which incident energy equals 1.2 cal/cm², representing the onset of a second-degree burn on unprotected skin.
Question 5: What minimum arc rating is required for PPE Category 1 per NFPA 70E?
- 4 cal/cm² (Correct answer)
- 8 cal/cm²
- 12 cal/cm²
- 40 cal/cm²
Correct answer: 4 cal/cm²
NFPA 70E Table 130.5(G) specifies that PPE Category 1 requires a minimum arc rating of 4 cal/cm².
Question 6: What does it mean for clothing to be 'arc-rated'?
- The clothing can safely conduct electricity
- The clothing has been tested and assigned an ATPV or energy breakopen threshold (Ebt) rating (Correct answer)
- The clothing is only flame retardant
- The clothing is rated for chemical splash protection
Correct answer: The clothing has been tested and assigned an ATPV or energy breakopen threshold (Ebt) rating
Arc-rated clothing has been tested per ASTM F1506 and assigned an ATPV or Ebt rating indicating the level of arc flash protection provided.
ESC ESC Arc Flash & PPE Selection 1
What causes an arc flash event?