What is the ASTM limiting oxygen index?

 

The limiting oxygen index is the lowest percentage of oxygen concentration in a gas mixture that will support a material that burns in the vertical direction to maintain a state of spontaneous combustion. In other words, it indicates a material's ability to inhibit the self-propagation of flame.

The principle of the LOI test is to expose the material to be tested to a specific mixture of atmospheres and observe whether the material is able to maintain a state of spontaneous combustion by gradually decreasing the oxygen concentration. When the oxygen concentration reaches a certain critical value, the material will not be able to sustain combustion, and this critical value is called the Limiting Oxygen Index (LOI).

 

A higher value of LOI indicates that the material is more resistant to combustion and has a lower oxygen demand, further preventing the spread of flame. Generally speaking, materials with an LOI of 21% or higher are usually considered good flame retardant materials.

 

As for your reference to "1200", I'm not sure exactly what that refers to, since ASTM LOI test results are expressed as a percentage. Please provide more contextual information and I will try to help you.