G3 Gas Properties and Combustion: What's Tested and How to Study It
Fuel properties, combustion air, flame characteristics and the numbers examiners keep coming back to.
This is the largest single area of the G3 syllabus and the one most likely to decide whether you pass. It is also the most memorisable: much of it comes down to a set of figures about natural gas and propane that either you know or you do not.
What does the G3 exam test on Gas Properties and Combustion?
Fuel properties, combustion air, flame characteristics and the numbers examiners keep coming back to. The question bank holds 318 questions in this area,
out of 1,184 across the whole syllabus.
Heat content, specific gravity and flammability limits for natural gas and propane
Air required for complete combustion, and what happens when there is not enough
Products of combustion, and the CO₂ levels above which carbon monoxide forms
Flame appearance — what a yellow flame is telling you
Boiling points, vapour behaviour, and why propane is treated differently
How should you study Gas Properties and Combustion for the G3 exam?
Learn the property table cold before anything else. A question asking which gas is heavier than air is free marks, and it appears in some form on nearly every attempt. Once the numbers are automatic, the reasoning questions get much easier — most of them are the same facts wearing a scenario.
Sample G3 exam questions on Gas Properties and Combustion
Five real questions from this topic, with the answers shown. The app holds
318 in this area alone, out of 1,184 across the whole syllabus.
What is the fire triangle?
Fuel, air, heat
✓ Fuel, oxygen, heat
Fuel, CO, CO₂
Fuel, nitrogen, heat
What is the chemical formula for methane, the primary component of natural gas?
C4H10
C2H6
C3H8
✓ CH4
What is the minimum dirt pocket size?
✓ 3 inches or the same as piping diameter, whichever is greater.
3 inches
4 inches
2 inches
What is the boiling point of propane at atmospheric pressure?
-260°F (-162°C)
32°F (0°C)
✓ -44°F (-42°C)
212°F (100°C)
When rescuing a victim of electrical shock, which action should you NOT take?
Call for emergency help
Disconnect the power source if possible
✓ Directly touch the victim while still in contact with the electrical source