Are flammability limits always defined with respect to fuel mixtures with air?

Flammability limits refer to the range of concentrations of a fuel in an oxidizer that are capable of sustaining combustion. While these limits are commonly defined using air as the oxidizer, they are not exclusively determined that way. Different oxidizers, such as pure oxygen or other gaseous mixtures, can also define flammability limits for specific fuels. Therefore, stating that flammability limits are always defined with respect to fuel mixtures with air is inaccurate, aligning with the choice of false.

Understanding flammability limits requires recognizing that the context can vary based on the environmental conditions, such as pressure and temperature, as well as the type of oxidizer involved. This is why the answer is correctly identified as false. It underscores that the behavior of fuels in different atmospheres—or in varying concentrations—can lead to different flammability characteristics and limits.