Which of the following values is acceptable for O2 levels after combustion in safe operation?

An acceptable value for O2 levels after combustion in safe operation typically falls within the range of 6-9%. This range indicates that there is a sufficient amount of oxygen present after combustion, which suggests effective burning of the fuel.

When O2 levels are too low, it may indicate incomplete combustion, leading to the production of harmful byproducts such as carbon monoxide (CO) and unburned hydrocarbons. Conversely, if the O2 levels are too high, as might be seen in higher ranges, it could indicate excess air is being supplied, which may be wasteful and could lower the overall thermal efficiency of the combustion process.

The 6-9% range signifies a balanced approach to combustion, where fuel is used efficiently while maintaining safety standards.