Safe use of flammable liquids outside of storage
NFPA Journal®, May/June 2011
In my last column, I discussed the use of flammable liquid storage cabinets, which are an important part of promoting housekeeping and protecting flammable and combustible liquids for a small fire exposure. It’s also important to address the use of flammable liquids outside of storage: How much flammable and combustible liquid may be located outside of storage at any one time?
NFPA 30, Flammable and Combustible Liquids Code, addresses the use and storage of flammable and combustible liquids. In this case, we are only discussing the incidental use of flammable and combustible liquids; other standards apply if the primary purpose of the operation is the manufacture or processing of flammable or combustible liquids. NFPA 318, Protection of Semiconductor Fabrication Facilities; NFPA 407, Aircraft Fuel Servicing; and NFPA 33, Spray Application Using Flammable or Combustible Materials, are some of the standards that may apply in manufacturing or processing operations.
Chapter 18 of NFPA 30, “Dispensing, Handling, Transfer, and Use of Liquids,” provides the detailed requirements for the incidental use of flammable and combustible liquids. Paragraph 18.104.22.168 states that the quantity of liquids outside storage areas, such as flammable liquid storage cabinets or storage rooms, shall be limited. Two quantities listed are not to be exceeded. One is the quantity of liquid needed for incidental operations for a 24-hour period. This quantity is not limited to a specified number of gallons, but depends solely on the operations conducted and the quantity of liquids necessary to support those operations for a 24-hour period.
The second quantity is a sum of liquids based on the class of liquid and the type of container or tank used. The total quantity that cannot be exceeded is the sum of the following: 25 gallons (95 liters) of class IA liquids in containers, where a container is a vessel not exceeding 119 gallons (450 liters) capacity; 120 gallons (454 liters) of Class IB, IC, II, or III liquids in containers; 20 portable tanks or intermediate bulk containers, each not exceeding 793 gallons (3,000 liters) of Class IIIB liquids; and 1,585 gallons (6,000 liters) of any combination of Class IB, IC, II, or IIIA liquids in metal portable or intermediate bulk containers, each not exceeding 793 gallons (3,000 liters), or Class II or Class IIIA liquids in nonmetallic intermediate bulk containers, each not exceeding 793 gallons (3,000 liters).
According to the standard, quantities in excess of these amounts will be stored in tanks. The quantity of liquids outside of safety cabinets or storage rooms should be limited to reduce the potential severity of a fire.
Another issue that must be considered when these liquids are outside of storage is the dispensing process. Dispensing liquids is also restricted by Section 18.4. Class I liquids shall only be transferred from original shipping containers, safety cans, portable tanks, or containers through the top with an anti-siphoning device or by gravity through a self-closing valve or self-closing faucet. Any Class II or III liquids heated above their flash point must be transferred as if they were a Class I liquid. The concern is that transferring Class I liquids produces flammable vapors that may be ignited by a local ignition source or even static electricity. By controlling how flammable liquids are dispensed, the standard reduces the spill potential and the production of potentially flammable vapors.
The basic handling requirements for flammable and combustible liquids have not changed significantly in the 2008 edition of NFPA 30. However, this 2008 edition is a complete editorial revision and includes many new items, including maximum allowable quantities, control areas, and specific requirements for occupancies.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is a former member of NFPA's Board of Directors.