When you look up the design and performance specifications of Flammable Liquid Safety Cabinets, whether you fefer to OSHA 1910.106 or NFPA 30 or FM Approvals, you will find the same standard:
Design, construction, and the capacity of storage cabinets.
Less than 60 gallons of Class I or Class II liquids, there is no more than 120 gallons of Class III liquids may be stored in a storage cabinet ( per OSHA ,NFPA slightly different).
Storage cabinets shall be designed and constructed to limit the internal temperature to not exceed 325 °F (163°C). when hit by a 10-minute fire test using the standard time-temperature curve as set forth in Standard Methods of Fire Tests of Building Construction and Materials, NFPA 251-1969, which is incorporated by reference as specified in §1910.6.
Design & Construction
Metal cabinets construction shall be deemed to be in compliance in the following ways. The bottom, top, the door, and both sides of cabinet shall be at least 18 gage sheet iron and double walled with 1 1/2-inch air space.Joints shall be riveted, welded, or made tight by some equally effective means. The door shall be provided with a three-point lock, and the door sill shall be raised at least 2 inches above the bottom of the cabinet.
Note: The time temperature curve as defined by ASTM E119, UL 263 and NFPA 251 is almost the same: Curve began in 68°F (20°C) at 0 minutes, continues to 1000°F (537°C) in 5 minutes, and for safety cabinets finishes at 1300°F(704°C) at 10 minutes as measured on the outside above the flame. The actual flame touching the cabinet can measure ≈1600°F (871°C).
Q:Where does the maximum 325ºF (163°C) internal temperature gain come from?
A: In surveying some of the typical flammable and combustible liquids; their auto ignition temperatures ranged from: 347°F (175°C) for Acetaldehyde, to 1139° F (615°C) for Aniline, with an outlier* of Carbon Disulfide at 194°F (90°C). （(According to the survey, most of ignition of flammable liquid between 175 ℃ to 615 ℃）
In conclusion, the safety cabinet burn test is conservative, representing a worst case scenario:
1. The test is conducted with pressurized fuel to reach the test’s specified heat within 10 minutes and the heat is applied on all four sides of the cabinet.
2. With the exception of the auto ignition outlier* of Carbon Disulfide at 194°F (90°C), the maximum allowable internal temperature gain of 325°F (162°C) is conservative as compared to the auto ignition temperature of most flammable and combustible liquids.