An interior tank allows the storage of larger quantities of flammable and combustible liquids. However, there are specific requirements for their design and construction that must be followed to protect not only workers but the general public and the environment.
A storage room for flammable chemicals must be built that meets the fire resistance classification required for their use. Must meet the following test specifications outlined in the National Fire Prevention Association, Standard Methods of Fire Tests of Building Materials and Construction, NFPA 251-1969:
- It is recommended that a storage room for flammable liquids be located along an exterior wall due to the danger of explosion.
- A fire protection system for an indoor storage room is a sprinkler, water mist, carbon dioxide, or other system that has been approved by local fire authorities.
- If there is an automatic sprinkler system, it must be designed and installed in accordance with code.
- The maximum size allowed for a storage room within a building is 500 square feet.
- Openings to other rooms or buildings must be provided with watertight, noncombustible raised sills or ramps at least 4 inches below the surrounding floor.
- Approved self-closing fire doors must be used.
- The room must be liquid-tight where the walls meet the floor.
- An open grated trench within the room that drains to a safe location may be an acceptable alternative to a sill or ramp. If many flammable liquids are being transferred in and out of the room using hand trucks, this might be preferable.
- Windows on other exposed properties or exposed parts of the building must be protected as described in the NFPA Standard for Fire Doors and Windows.
- Electrical wiring and equipment located in an indoor storage room used for Class I liquids must be approved under Subpart S, Electrical, for Class I, Division 2 hazardous locations. If storing only Class II and Class III, wiring electrical must be approved for general use.
- An approved ventilation system must be installed.
Since flammable vapors are heavier than air, they hang close to the floor and can collect and move toward sources of ignition or other incompatible chemicals. The ventilation system is vital to prevent flammable vapors from building up enough to cause an explosion or liquid fire. Each indoor storage room must have a mechanical or gravity exhaust system that provides a complete change of air within the room at least 6 times per hour. The switch for a mechanical ventilation system also controls all lighting in the room and should be located outside of the storage room. If gravity ventilation is provided, the fresh air inlet and exhaust outlet for the room should be on the outside of the building in which the storage room is located.
Additional requirements:
- Within each storage room, an aisle at least 3 feet wide must be maintained to allow for easy movement around the room. This is necessary to reduce the possibility of containers being spilled or damaged and to provide firefighting access and a ready escape route from the room if a fire occurs.
- If wood is used for shelving, it must be at least 1 inch thick and can also be used for slats, dunnage, trim, floor covering, etc.
- Chemicals should not be stored on unfinished wooden shelves. Finished metal or high density plastic (polypropylene) shelving is recommended for most chemicals. If wood is used it should be sealed with a good quality oil based paint, natural or synthetic varnish.
- Proper separation of chemicals must be maintained within the storage room. Incompatible chemicals should be stored away from each other or possibly in divided areas.
- Chemicals should be stored at eye level to reduce the chance of spillage or breakage and to facilitate identification.
- Labels must be complete, legible and up-to-date.
- MSDS information must be available for all stored chemicals.
- At least 1 portable fire extinguisher with a rating of not less than 12 B units must be located outside the storage room, not more than 10 feet from the door leading to the room.
- Materials that react with water should not be stored in the same room with flammable or combustible liquids.
- Containers larger than 30 gallons in capacity should not be stacked on top of others.
Chemical supply is by an approved pump, self-closing tap or closed piping system. If flammable liquids are dispensed within the storage room, a pilot light must be installed next to the switch.
Storage capacity
- This depends on the availability of a sprinkler system and the fire rating of the storage room. One with a 2-hour fire resistance and equipped with sprinklers can store a larger amount of chemicals.
- If there is fire protection in a room that has a 2-hour fire resistance rating, the allowable storage is 10 gallons per square foot.
- If there is no fire protection in this room, 4 gallons of chemicals per square foot are allowed.
- In a room that has a 1-hour fire rating, with fire protection, storage space is reduced to 150 square feet.
- The amount of flammable chemicals that can be stored in this room is 5 gallons per square foot.
- A room that has no fire protection and a 1-hour fire rating can store 2 gallons of flammable chemicals per square foot.