G3 Core Concepts and Principles 2 — Questions and Answers
Question 1: What is the primary component of natural gas used in Ontario residential heating?
- Propane
- Methane (Correct answer)
- Butane
- Ethane
Correct answer: Methane
Natural gas is primarily methane (CH4), making up 85-95% of the mixture.
Methane's properties including heating value and combustion characteristics are fundamental to gas appliance operation and sizing.
Question 2: What does 'specific gravity' mean in relation to natural gas?
- The temperature at which gas ignites
- The ratio of gas density to air density (Correct answer)
- The pressure at which gas is delivered
- The volume of gas consumed per hour
Correct answer: The ratio of gas density to air density
Specific gravity compares gas density to air density, with air at 1.0.
Natural gas has a specific gravity of approximately 0.60, meaning it is lighter than air and rises, affecting ventilation requirements and gas detector placement.
Question 3: What is the approximate heating value of natural gas per cubic foot?
- 500 BTU/ft³
- 1,000 BTU/ft³ (Correct answer)
- 1,500 BTU/ft³
- 2,500 BTU/ft³
Correct answer: 1,000 BTU/ft³
Natural gas has approximately 1,000 BTU per cubic foot.
This value is used to calculate gas consumption rates, size piping, determine appliance input ratings, and verify meter readings.
Question 4: What are the three elements of the fire triangle?
- Gas, electricity, and air
- Fuel, oxygen, and heat (ignition source) (Correct answer)
- Methane, nitrogen, and a spark
- Pressure, temperature, and volume
Correct answer: Fuel, oxygen, and heat (ignition source)
The fire triangle requires fuel, oxygen, and heat. Removing any one prevents combustion.
Understanding this concept is critical for safe operation and emergency response—removing any element stops combustion.
Question 5: What is the flammable range of natural gas in air?
- 1% to 5%
- 5% to 15% (Correct answer)
- 15% to 25%
- 25% to 50%
Correct answer: 5% to 15%
Natural gas has a flammable range of approximately 5% to 15%. Outside this range it will not ignite.
Gas detection equipment is calibrated to measure concentration as a percentage of LEL, with alarms typically set at 10-25% of LEL for early warning.
Question 6: Why is mercaptan added to natural gas?
- To increase the heating value
- To give it a detectable odour for leak detection (Correct answer)
- To reduce carbon monoxide production
- To lower the ignition temperature
Correct answer: To give it a detectable odour for leak detection
Mercaptan is added because natural gas is naturally odourless, enabling leak detection by smell.
The concentration is set so gas can be detected at approximately one-fifth of its lower explosive limit, providing an important safety margin.
G3 Core Concepts and Principles 2
What is the primary component of natural gas used in Ontario residential heating?