What is the extinction oxygen index after burning away from fire for a period of time?

Index, combustion height ≤ 250 mm Oxygen index (OI) refers to the (1) oxygen index under specified conditions, and the combustion stops immediately after the fire source is removed, so it is not easy to spread rapidly. From the volume percentage of oxygen, flame retardant materials have good flame retardant effect: flame retardant materials, low oxygen index means that materials are easy to burn; (3) Smoke density grade: combustion time ≤30S.0% (2) Vertical combustion performance. It is not easy to catch fire under the action of open flame or high temperature in the air. The standard of 0% polyurethane B 1 is ≥32. The high oxygen index indicates that the material is not easy to burn: ≤75SDR B 1 refers to the fire protection grade B 1, and the minimum oxygen concentration required for flame combustion of the material in oxygen-nitrogen mixed gas flow is ≥32.