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June 2012: Storage Tanks for Flammable Liquids

You may be considering adding one or more tanks that contain ignitable (flammable and combustible) liquids at your facility. FM Global Data Sheet 7-88, Storage Tanks for Flammable Liquids, gives guidance on how these tanks should be installed and protected.

Whenever possible, these tanks should be of noncombustible construction and protected from corrosion. There are instances where liquids are not compatible with noncombustible materials and combustible materials must be used. If this is the case, then additional provisions would be needed. These include, but are not limited to containment arrangements, tank orientation, tank support, and bonding and grounding.

Supports for tanks should be arranged so they do not fail due to the heat released from a fire involving these liquids. A tank failure is very likely if supports fail. The preferred method of accomplishing this is to provide supports that can withstand a flammable liquids fire in this area for at least 2 hrs. If steel supports are used, then they should be coated with a material with a minimum 2 hr. fire rating. If this cannot be provided, then automatic sprinkler protection should be provided to cool these supports.

Tanks should also be located safe distances from buildings and each other. These separation distances vary based on the liquid being stored and the size of the tanks. Fill lines should terminate near the bottom of tanks and dispensing pipes should exit the top of the tank. Additionally, hydrant protection should be provided such that two different hydrants can be used for each tank present.

Natural hazards should also be considered. Earthquake bracing, seismic shut-off valves, and appropriate flexible piping connections should be provided in areas prone to earthquakes. In flood prone areas, tanks should be located so at least 30% of their allowable storage capacity is above the 100 yr. flood level. If this cannot be accomplished, then tanks should be anchored to resist floating or filled so vacated space of the tank is not below the 100 yr. flood area. Additionally, tanks openings that are not water tight should be extended above the 100 yr. flood level.

Containment should also be provided for tanks with ignitable liquids. Containment provisions will vary based on how much liquid and how many tanks are present. This will determine the capacity of the containment as well as if any subdivisions will be needed. Outdoor containment areas should be provided with an impounding basin at a safe location to remove rain water and such from the containment area.

Indoor tanks have size provisions based on the flashpoint of the liquid and the floor that these tanks are located on. The harder fire department access will be, then smaller the tanks should be. Additionally, indoor tanks should have additional safeties such as: leak detection, should be hard piped to an exterior fill location with interlocks, and should be vented to the outside. Automatic sprinkler protection should also be provided for indoor tanks.

When liquids with low flashpoints or that are heated to within 25° F of their flashpoint are present, rated electrical equipment should be used within the cut-off room or within 10 ft. of tank openings when not located in a cut-off room. Conductive piping should also be used with bonding and grounding. Hot work and smoking should also not be allowed in or near these tanks.

Risk Logic can help you determine what should be provided for your facility if you are considering any tanks for ignitable liquids at your facility. Please contact us for additional information.