The fire rating of polyurethane cold storage board can be classified by the size of the oxygen index (the specific value needs to be tested by professional measurement units), such as:
B1 grade polyurethane cold storage board: oxygen index of combustion test ≧32.
B2 grade polyurethane cold storage board: combustion test oxygen index ≧26.
Grade B3 polyurethane cold storage board: combustion test oxygen index < 26.