The Solvent Cabinet - A Laboratory Super Hero
The purpose of a solvent or flammable cabinet is to protect the flammables inside in the event that the laboratory is on fire. The accepted standard on cabinet construction is National Fire Protection Association (NFPA) 30, Flammable and Combustible Liquids Code Handbook, with Underwriter’s Laboratory (UL) and Factory Mutual (FM) offering third party evaluation of cabinet construction and performance.
Solvent cabinets typically have a double wall; this acts as in insulator from potential exterior heat. They also have a solid steel top, even if a work surface is to be placed over the cabinet. Cabinet doors are also double walled, and should have three point latching systems.
A common feature is self-closing doors with a fusible link. If the self closing doors are latched open, and the laboratory is on fire, the fusible link will allow the doors to close if the temperature reaches 165 degrees F.
Additionally, these cabinets usually have a grounding feature to prevent the discharge of static electricity. All cabinets designed to store solvents are easily identified with a bold note in red lettering: FLAMMABLE, KEEP FIRE AWAY.
A Factory Mutual Listing on a solvent cabinet means that it was tested and approved by Factory Mutual to meet Factory Mutual Approval Standard 6050. The introduction of the Standard states that “The requirements of this standard are based on experience, research and testing, and in large part on NFPA 30.”
Carrying the FM listing also means the manufacturer has agreed to facility audits. Ongoing product audits are part of the Approved Product Follow-Up Program, and are required to maintain the FM Listing.
The Underwriters Laboratory 1275 label for cabinets and FM listings are largely the same, and both are based on NFPA 30. NFPA 30 Chapter 4.3.3 (a) states, “Storage Cabinets shall be designed and constructed to limit the internal temperature at the center, 1 inch (2.5 cm) from the top, to not more than 325 degrees F (162.8 degrees C) when subjected to a 10-minute fire test with burners simulating a room fire exposure using the standard time temperature curve as given in NFPA 251, Standard Methods of Fire Tests of Building Construction and Materials. All joints and seams shall remain tight and the door shall remain securely closed during the fire test.” This is the core of both UL and FM solvent cabinet evaluations, and the reason for the robust construction of solvent cabinets.
According to NFPA Code 30, 9.5.4*, "The cabinet is not required to be vented for fire protection purposes." Because flammable and combustible liquid storage cabinets are designed to protect the internal contents from a fire outside the cabinet, a vented cabinet could compromise the ability of the cabinet to protect its contents from a fire.
NFPA Code 30 clearly dismisses the need to vent storage cabinets in its appendix. Under A.9.5.4 it states: “Venting storage cabinets has not been demonstrated to be necessary for fire protection purposes. Additionally, venting a cabinet could compromise the ability of the cabinet to adequately protect its contents from involvement in a fire since cabinets are not generally tested with venting. Therefore, venting of a storage cabinet is not recommended." However, because of differing priorities, Health and Safety people typically recommend that solvent storage cabinets be kept under negative pressure. The goal being to prevent unneeded exposure to solvent vapor each time the cabinet is opened.
Additionally, solvent vent kits are still required by code in certain places. NFPA 30 Section 188.8.131.52 states, "If vented for whatever reason, the storage cabinet vent openings shall be ducted directly to outdoors in such a manner that will not compromise the specific performance of the cabinet and in a manner that is acceptable to the authority having jurisdiction." If local code, building safety officer, architect, or lab planner requires the use of a solvent vent kit, solvent cabinet manufacturers typically have kits available. These kits should be made of fire proof materials. They attach to the back of the solvent cabinet, and should be routed to an appropriate dedicated ventilation source.
At the point of connection to the cabinet, the manufacturer should provide a flame (or spark) arrestor. The flame arrestor, which occupies the vent hole, will prevent any potential fire from reaching the interior of the cabinet through the vent pipe. By forcing a flame front through channels too narrow to permit the continuance of flame (typically a fine mesh screen) a flame arrestor is designed to extinguish a flame and stop fuel combustion. NFPA 30 Section 184.108.40.206 notes that “If the cabinet is not ventilated, storage cabinet vent openings shall be sealed with the bungs supplied with the cabinet or with bungs specified by the manufacturer."