CFI CFI Electrical & Mechanical Fire Causes 2 — Questions and Answers
Question 1: In investigating a mechanical fire cause, which component failure in internal combustion engines is most commonly associated with vehicle fires?
- Alternator failure
- Fuel system leaks ignited by hot engine components or electrical sparks (Correct answer)
- Brake system overheating
- Coolant system failures
Correct answer: Fuel system leaks ignited by hot engine components or electrical sparks
Fuel system leaks that allow flammable fuel to contact hot engine surfaces or electrical ignition sources are the most common mechanical cause of vehicle fires.
Question 2: What mechanical condition can cause a dryer to start a fire even without electrical faults?
- Drum bearing failure
- Lint accumulation in the exhaust duct restricting airflow and causing overheating (Correct answer)
- Motor overload due to heavy loads
- Belt slippage reducing rotation speed
Correct answer: Lint accumulation in the exhaust duct restricting airflow and causing overheating
Lint accumulation in dryer exhaust ducts restricts airflow, causing the dryer to overheat, and the highly flammable lint itself can ignite from the heat.
Question 3: What is 'friction heating' as a fire cause in mechanical equipment?
- Heat generated when two dry surfaces rub together during normal operation, causing ignition of nearby combustibles (Correct answer)
- Electrical resistance heating in motors
- Heat from combustion in engines
- Thermal radiation from hot equipment surfaces
Correct answer: Heat generated when two dry surfaces rub together during normal operation, causing ignition of nearby combustibles
Friction heating occurs when mechanical parts rub against each other due to lubrication failure or mechanical misalignment, generating enough heat to ignite nearby combustibles or the material itself.
Question 4: When investigating a fire of suspected mechanical origin involving rotating equipment, what physical evidence should an investigator look for at the origin?
- V-patterns pointing toward the motor
- Seized bearings, worn or scored shafts, displaced belts, and evidence of lubricant failure (Correct answer)
- Arc beads on nearby wiring
- Accelerant residue near the equipment base
Correct answer: Seized bearings, worn or scored shafts, displaced belts, and evidence of lubricant failure
Physical evidence of mechanical failure including seized bearings, scoring, belt displacement, and lubricant breakdown indicates friction or overheating as the ignition source.
Question 5: Which NFPA standard provides the most comprehensive guidance on vehicle fire investigation?
- NFPA 1033
- NFPA 921 (Correct answer)
- NFPA 555
- NFPA 72
Correct answer: NFPA 921
NFPA 921, 'Guide for Fire and Explosion Investigations,' includes dedicated chapters on vehicle fire investigation methodology and physical evidence analysis.
Question 6: What is a 'spontaneous ignition' fire cause, and which material is most commonly associated with it?
- A fire caused by lightning, most common in open fields
- Self-heating of a material to its ignition temperature without an external ignition source, most common with oily rags or linseed oil-soaked materials (Correct answer)
- Combustion caused by friction, most common in industrial machinery
- A fire caused by sunlight concentration, most common with glass objects
Correct answer: Self-heating of a material to its ignition temperature without an external ignition source, most common with oily rags or linseed oil-soaked materials
Spontaneous ignition (or spontaneous combustion) occurs when a material self-heats through oxidation to its ignition temperature, and oily rags soaked in linseed oil or similar drying oils are the most common example.
CFI CFI Electrical & Mechanical Fire Causes 2
In investigating a mechanical fire cause, which component failure in internal combustion engines is most commonly associated with vehicle fires?