What does point "C" on the flammable range diagram indicate?

Point "C" on the flammable range diagram indicates the lower explosive limit (LEL). The LEL is the lowest concentration of a vapor in the air that can ignite and cause a fire or explosion when an ignition source is present. Understanding the LEL is critical for safety in environments where flammable materials are handled, as it helps determine the minimum level of vapor required for combustion to occur.

In a flammable range diagram, the area between the LEL and the upper explosive limit (UEL) defines the concentration range where a substance can ignite. Below the LEL, the fuel-air mixture is too lean to support combustion, while at concentrations above the UEL, it is too rich for ignition. This is fundamental knowledge for ensuring safe operations with flammable substances, particularly in industries like shipping, oil and gas, and manufacturing.

The other points of interest, such as flash point and fire point, pertain to different characteristics of flammable materials. The flash point is defined as the lowest temperature at which a liquid can form an ignitable mixture with air, while the fire point is the temperature at which the liquid will continue to burn after being ignited. These concepts are important but do not define the conditions represented by point "C"