Gas Safe ACS - Accredited Certification Scheme Combustion Principles Questions and Answers

Question 1

Which of the following are the three essential components required for combustion, often referred to as the 'combustion triangle'?

Accepted Answer

Fuel, Heat, and Oxygen

Answer

The combustion triangle illustrates the three elements needed for fire to occur: a fuel source to burn, sufficient heat to raise the fuel to its ignition temperature, and an oxidising agent, which is usually oxygen from the air. Removing any one of these components will prevent or extinguish a fire.

Question 2

An engineer is commissioning a new gas boiler. They observe a lazy, yellow-tipped flame on the main burner. What is the most likely cause of this?

Accepted Answer

Incomplete combustion due to insufficient primary air

Answer

A yellow or orange, lazy flame is a classic visual sign of incomplete combustion. This occurs when there is not enough oxygen mixing with the gas, leading to the production of soot (which glows yellow) and dangerous carbon monoxide. Insufficient primary air entrainment at the burner is a primary cause of this condition.

Question 3

According to BS 7967, when using a portable flue gas analyser, what is the primary ratio used to assess the combustion safety of a gas appliance?

Accepted Answer

CO / CO2 ratio

Answer

British Standard BS 7967 provides guidance on the use of electronic portable combustion gas analysers. It specifies action levels based on the ratio of Carbon Monoxide (CO) to Carbon Dioxide (CO2) in the flue gases. This ratio is a key indicator of how completely the fuel is being burned and is used to determine if an appliance is safe or requires remedial action.

Question 4

What are the main products of the complete combustion of natural gas (methane)?

Accepted Answer

Carbon Dioxide (CO2) and Water Vapour (H2O)

Answer

When natural gas (which is primarily methane, CH4) burns completely with a sufficient supply of oxygen, the hydrocarbon fuel is fully oxidized. This chemical reaction produces harmless Carbon Dioxide (CO2) and Water Vapour (H2O), releasing heat energy in the process.

Question 5

A gas engineer is investigating a report of an intermittent smell of fumes from an open-flued gas fire. A spillage test is conducted. According to standard procedures, when should this test be performed?

Accepted Answer

After the appliance has been running at maximum rate for 5 minutes

Answer

Standard UK gas safety procedures require a spillage test (or flue draw test) to be performed on open-flued appliances to ensure products of combustion are being safely removed. The test should be carried out within five minutes of the appliance being lit, and if spillage is detected, the appliance should be left to run for a further 10 minutes before re-testing to allow the flue to warm up and establish a proper draw.

Gas Safe ACS Practice Test

Gas Safe ACS Practice Test

Gas Safe ACS - Accredited Certification Scheme Combustion Principles Questions and Answers