At concentrations above the upper explosive limit (UEL), the fuel has displaced enough air that what occurs?

At concentrations above the upper explosive limit (UEL), the fuel has displaced enough air that what occurs?

• A. An inadequate level of oxygen is present to initiate a reaction
• B. There is excessive oxygen causing rapid combustion
• C. The mixture becomes nonflammable
• D. An ignition source is required for ignition

Answer: (A)

At the upper explosive limit, the mixture is too fuel-rich because the excess fuel has displaced much of the air, reducing the oxygen concentration below what’s needed to support a flame. Without enough oxygen, a reaction can’t be initiated even if an ignition source is present. That’s why the correct idea is that there is an inadequate level of oxygen to initiate combustion.

At the upper explosive limit, the mixture is too fuel-rich because the excess fuel has displaced much of the air, reducing the oxygen concentration below what’s needed to support a flame. Without enough oxygen, a reaction can’t be initiated even if an ignition source is present. That’s why the correct idea is that there is an inadequate level of oxygen to initiate combustion.