G3 - Gas Technician Level 3 Properties of Fuel Gases Questions and Answers

Question 1

A gas technician is investigating a reported gas odor in the basement of a residence. Which property of propane (LPG) is most critical to consider in this scenario?

Accepted Answer

Its specific gravity is greater than air, causing it to accumulate in low areas.

Answer

Propane has a specific gravity of approximately 1.52, making it heavier than air (specific gravity of 1.0). This means that if a leak occurs, the propane gas will sink and collect in low-lying areas like basements, creating a significant safety hazard. Natural gas, with a specific gravity of about 0.6, is lighter than air and would dissipate upwards.

Question 2

Which of the following statements accurately compares the heating value of natural gas and propane?

Accepted Answer

Propane has a significantly higher heating value per cubic foot than natural gas.

Answer

Propane has a much higher energy content by volume compared to natural gas. A cubic foot of propane yields approximately 2,500 BTUs, whereas a cubic foot of natural gas yields about 1,000-1,030 BTUs. This difference is crucial for appliance orifice sizing and system design.

Question 3

Incomplete combustion of a hydrocarbon fuel, such as natural gas or propane, occurs due to insufficient oxygen. What is the primary toxic gas produced as a result?

Accepted Answer

Carbon Monoxide (CO)

Answer

When there is not enough oxygen for complete combustion, the burning process is incomplete and produces carbon monoxide (CO), a colorless, odorless, and highly toxic gas. Complete combustion ideally produces carbon dioxide (CO2) and water vapor.

Question 4

The 'flammable range' or 'explosive limits' of a fuel gas refers to the concentration of gas in a gas-air mixture that will support combustion. What defines the Lower Explosive Limit (LEL)?

Accepted Answer

The minimum concentration of gas in air that will burn.

Answer

The Lower Explosive Limit (LEL), also known as the Lower Flammability Limit (LFL), is the lowest concentration (percentage) of a gas or vapor in the air that is capable of producing a flash of fire when an ignition source is present. A mixture below the LEL is considered 'too lean' to burn.

Question 5

A technician is converting a furnace from natural gas to propane. What fundamental property difference requires the technician to change the orifices?

Accepted Answer

Propane has a higher heating value and requires a different air-to-gas ratio.

Answer

Propane has a higher heating value (approx. 2,500 BTU/ft³) than natural gas (approx. 1,000 BTU/ft³). To deliver the correct amount of energy and ensure complete combustion, a smaller orifice is needed for propane to restrict the higher-energy fuel flow. Propane also requires a different air-to-gas ratio for combustion (approx. 24:1) compared to natural gas (approx. 10:1).

G3 - Gas Technician Level 3 Certification Practice Test

G3 - Gas Technician Level 3 Certification Practice Test

G3 - Gas Technician Level 3 Properties of Fuel Gases Questions and Answers