So you are purchasing an FR garment for your employees and there is a data sheet with a laundry-list of numbers that don't make any sense to you…let's decode that.
The first number we will cover is the Limiting Oxygen Index or LOI. This is defined as the minimum oxygen percentage needed to sustain a flame. Oxygen being part of the combustion triangle, this number is used as a proxy of the flammability of a fabric and comparing it to others. Its real world usage is not very pragmatic as encountering a hyperoxic environment outside of a decompression chamber is likely rare.
So how should you interpret the numbers you see? In normal room air, there is about 21% oxygen and 79% nitrogen with some other trace gasses sprinkled in. The testing is done by placing the fabric in a chamber that is progressively mixed with more oxygen and less nitrogen until combustion is achieved. Essentially, the higher the LOI, the more oxygen is needed to support combustion of the material and therefore the more flame resistant the material is. The scales vary slightly but in general if something has a LOI of 28 or greater, it is considered self extinguishing in normal atmospheric conditions and non-combustible. The meta-aramid in the AzoShield 211 FR glove has a LOI of about 28 and the para-aramid has a LOI of about 30. This is in comparison to something like cotton, which generally has a LOI around 18.
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