ACS Combustion & Flues

Question 1

What is the product of complete combustion of natural gas (methane)?

Accepted Answer

Carbon dioxide and water vapour

Answer

Complete combustion of methane (CH4) produces carbon dioxide (CO2) and water vapour (H2O) — CO2 and water are the safe end products when sufficient oxygen is present.

Question 2

What is carbon monoxide (CO) and why is it particularly dangerous?

Accepted Answer

An odourless, colourless, tasteless gas that binds to haemoglobin with far greater affinity than oxygen, causing rapid incapacitation and death

Answer

CO has approximately 250 times the affinity for haemoglobin that oxygen does — it prevents oxygen being carried by the blood, causing oxygen starvation that can be rapidly fatal without any warning to the victim.

Question 3

What does a high CO/CO2 ratio (Wobbe index deviation) in flue gas analysis indicate?

Accepted Answer

Incomplete combustion is occurring, likely due to insufficient air supply, a dirty burner, or flue restriction

Answer

A high CO:CO2 ratio indicates incomplete combustion — too much carbon monoxide relative to carbon dioxide is a sign that the combustion process is not burning the fuel fully, producing dangerous CO levels.

Question 4

What is the primary air/secondary air function in a gas burner?

Accepted Answer

Primary air mixes with gas before the burner to support combustion; secondary air provides additional oxygen around the flame to complete combustion

Answer

Primary air is entrained by the gas flow upstream of the burner to create a combustible mixture; secondary air enters around the flame to provide additional oxygen for complete combustion.

Question 5

What does a 'balanced flue' on a gas appliance mean?

Accepted Answer

The appliance draws its combustion air from outside and expels flue gases to outside through a co-axial terminal, making it room-sealed and unaffected by internal air quality

Answer

A balanced (room-sealed) flue has a concentric terminal — combustion air is drawn from outside and flue gases are expelled outside, so the appliance is entirely sealed from the room and unaffected by negative pressure or lack of ventilation.

Gas Safe ACS Practice Test

Gas Safe ACS Practice Test

ACS Combustion & Flues