Strainer Fire Proof Level
Strainer fire proof rating, American UL Underwriters Laboratories Standard, UL-900-1997
Class 1
Strainer (when clean) does not burn when meets fire, only a very small amount of smoke distribution
Class 2
Strainer (when clean) has a slight burning when meets fire, or distribute a limited smoke, or both simultaneously happens.
Strainer structure and fire protection classification, the United States Institute of Environmental Science and Technology, IES-RP-CC001.3-1993
Grade 1：
Non-combustible structure, can withstand the harsh environment, structure is firm. Mainly used in military, atomic energy, important industries.
To meet the U.S. Military Standard MIL-F-51068.
Grade 2：
Flame-retardant structure, passed the water resistant test, low temperature resistant testing, as well as the military standard MIL-F-51068 part experiment.
To meet the United States UL-586 standard test (flame test).
Grade 3：
Do not burn when meets fire, only distribute trace of smoke. Comply with one level of UL-900 standard.
Grade 4：
A slight burning when meets fire, or distribute a limited smoke. Comply with second level of UL-900 standard.
Grade 5：
Flame-retardant material structure, no combustion-supporting material, when meets fire only produces a small amount of smoke or do not produce smoke. For air filtration at the top or side clean room blowing parts.
Grade 6：
For the places with no special requirements for fire protection and non-essential.
