At what concentration of oxygen is combustion likely to occur?

Combustion is a chemical process that typically requires a minimum concentration of oxygen to sustain the flame. The correct answer, which indicates a range of 15 to 16 percent oxygen concentration, aligns with established scientific principles regarding fire behavior.

In air, which consists of approximately 21 percent oxygen, combustion is most effectively supported. Oxygen concentrations lower than 15 percent can significantly hinder the combustion process; as the oxygen level drops, the likelihood of ignition and sustaining a fire decreases. Conversely, concentrations higher than 21 percent, while still suitable for combustion, are usually not a concern in normal atmospheric conditions.

The range of 10 to 12 percent presented in the alternative choices is too low for effective combustion in most typical scenarios, as combustion generally becomes more difficult at oxygen concentrations below 15 percent. Meanwhile, 20 to 22 percent also indicates ample oxygen availability for ignition and sustenance of fires, but it doesn't present the minimum threshold where combustion is likely to occur. Lastly, the concentration of 5 to 7 percent is far too low, as it is significantly below the required threshold for any practical combustion processes.

Understanding these thresholds is essential for fire investigators in assessing fire scenes and analyzing whether combustion occurred and under what conditions.