The way OI test assesses the flammability or fire resistance of a material is quite straightforward:

The way OI test assesses the flammability or fire resistance of a material is quite straightforward:

1. If a material has a high oxygen index, that means a high concentration of oxygen is needed to sustain a flame. Therefore, it’s considered less flammable or more fire-resistant. 

2. Conversely, a lower oxygen index means the material needs less oxygen to maintain combustion, indicating that it’s more flammable or less fire-resistant.

It’s important to note that the oxygen concentration in the Earth’s atmosphere is about 21%. So, a material with an oxygen index lower than 21% is considered highly flammable since it can burn in regular atmospheric conditions. A material with an OI higher than 21% would be considered relatively fire-resistant in normal atmospheric conditions, as it wouldn’t sustain a flame without an enriched oxygen environment.