Which of these is NOT a factor in determining an explosion's potential?

The concentration of combustible material, the presence of an ignition source, and the temperature of the combustible material are all critical factors in determining the potential for an explosion.

The concentration of combustible material is essential because there needs to be a specific amount of fuel available to maintain a combustion reaction once it starts. Similarly, the presence of an ignition source is crucial since this source provides the necessary energy to initiate combustion. Temperature is also vital; if the combustible material is at a high enough temperature, it can more easily ignite and contribute to an explosion.

In contrast, while humidity plays a role in influencing the behavior of certain materials and can affect their flammability, it is not a direct factor in determining the potential for an explosion. Therefore, it is the factor that does not directly influence the chances of an explosion occurring compared to the others listed, which are fundamental to explosion dynamics.