OSHA Flammable Liquid Storage Requirements

OSHA mandates safe storage of flammable liquids, which are liquids with flashpoints below 100 degrees F. (Flashpoint is the lowest temperature at which the liquid gives off enough vapor to ignite.) OSHA Subpart H, Hazardous Materials, sets standards for construction of storage tanks, pipes, fittings and valves and the tanks' location. The standard also outlines safe small scale and short term storage of flammables.

Tank Construction

• Tanks that contain flammable liquids must be made of steel. The two exceptions are for tanks that will be stored underground and tanks that will hold liquids that are incompatible with steel. A tank made of any material other than steel must comply with engineering principles approved by American Petroleum Institute and the American Society of Mechanical Engineers. Manufacturers or repair persons who weld or bolt tanks must use a nonferrous filler metal or alloy with a melting point higher than 1000 degrees F. Tank designers who expect a flammable material to corrode the inside of a tank must reinforce the inside of the tank to compensate for this corrosion. The designer must determine the adequate level of internal reinforcement based on expected life of the tank.

System Design

• Process operators must mark tank connections, the points at which tanks are filled or emptied, so they are easy to find. OSHA requires these connections to be kept closed and liquid tight when no one is filling or emptying the tank. Connections must be outdoors and at least 5 feet from any opening in any building. OSHA mandates all above ground tanks have a pressure relief device. Exposure to flame could cause pressure inside the tank to build up, and this device must allow internal pressure to escape. Based on tank location and orientation, OSHA allows construction features such as a floating roof or a weak roof-to-shell seam, which would fail before any other seam in the tank.

Above Ground Tank Spacing

• OSHA restricts the spacing between flammable liquid storage tanks. Industrial producers must space above ground tanks at least one sixth the sum of the tanks' diameters, and not closer than 3 feet. Producers and refiners who set adjacent tanks of unstable flammable liquids must leave a distance between the tanks equal to at least half the sum of the tanks' diameters. Operations that use three or more rows of tanks must allow enough space between tanks for firefighters to get through. Emergency responders must also be left enough room to work around tanks that are set into an irregular pattern.

Underground Tank Location

• OSHA instructs industrial producers to place underground tanks carefully so buildings' foundations cannot transfer weight load to tanks. Site designers must place flammable storage tanks at least one foot from a basement wall, and at least 3 feet from a property line. Workers must place the tank on a firm 6-inch (minimum) foundation of earth, gravel or sand. Workers then cover the tank with 2 feet of dirt or one foot of dirt plus a 4-inch reinforced concrete slab. If the tank is buried under a road, driveway or area that is likely to be driven over, the operators must bury the tank 3 feet deep or 1.5 feet deep covered by a 6-inch reinforced concrete slab. If the slab is asphalt rather than concrete, operators must make sure it is 8 inches thick and extends one foot past the tank in every direction.

Short Term Storage

• OSHA addresses small scale and short term storage of flammable liquids in tables H-12 and H-13 of Standard 1910.106. Table H-12 lists maximum permitted container sizes for liquid storage containers and portable tanks. Flammable liquids are classed according to various properties, and table H-12 provides maximum volumes workers may keep in containers of different materials. Table H-13 lists how many gallons of a flammable liquid may be stored in a room based on the room's size, hours of fire resistance (a construction standard based on thickness and types of building materials) and whether firefighting systems (such as sprinklers) are present.