Bellow what oxygen concentration can combustion not be supported?

Combustion requires a certain concentration of oxygen in the atmosphere to sustain a fire. The generally accepted minimum concentration of oxygen necessary to support combustion is around 16%. However, when oxygen levels drop below about 5%, combustion cannot be supported at all. Thus, combustion will not occur under conditions where the oxygen concentration is 3% or lower.

In this context, the choice indicating that combustion cannot be supported at an oxygen concentration of 3% is accurate. At this level, there is insufficient oxygen available to maintain the chemical reactions necessary for fire. The understanding of these oxygen concentration thresholds is critical for fire safety and prevention measures, as it directly influences firefighting strategies and determines safe environments for personnel.

Options falling above this threshold, such as 5% and 10%, while low, still provide enough oxygen for potential combustion under certain conditions. Consequently, these options would not be valid answers to the question about where combustion cannot be supported.