Fixed or Semi-Fixed Fire Protection Systems for Storage Tanks In the early years of the oil industry, fire in a storage Listed below are types of tanks commonly used for tank was a common occurrence. Virtually all the storage of combustible or flammable liquids. products were stored in cone roof tanks built of riveted steel plates and the roof was often • Cone roof tank constructed with wood and tar coated paper. Tank • Open top floating roof tank fires were common especially after a lightning • Internal floating roof tank/covered floating roof storm. This costly experience gradually led to improvements in better codes and guidelines for Cone Roof Storage Tank has vertical sides and is handling storage tank fires. Floating roof tanks equipped with a fixed cone-shaped roof that is were adopted for low flash point petroleum products welded to the sides of the tank. Tanks that have and proved to be a most reliable method of been designed in accordance with API standards protection against losses due to fires. The less have a weak seam at the joint where the roof and volatile products with higher flash points continue to sides meet. In the event of an internal explosion, be stored in welded steel cone roof tanks. the roof separates and blows off leaving the tank shell intact. This system allows the tank to retain its As the frequency of fully involved storage tank fires contents and any resulting fire will involve the full decreases to a more acceptable level, the size of surface of the exposed flammable liquid. fire, when it happens, becomes larger due to the increase in tank size and capacity. It is quite Open Top Floating Roof Storage Tank is similar common to see tanks with diameters in excess of to the cone roof tank in construction but with the 328 ft. (100 meters) capable of storing a million exception that it has no fixed roof. A pontoon type barrels of product. roof floats directly on the flammable liquid surface. This floating roof has a mechanical shoe or tube One practical method to protect flammable liquid seal attached to its full perimeter. The rim seal storage tanks from fire is with a fixed or a semi- covers the space between the floating roof and the fixed foam fire protection system. When tank shell (side wall). engineered, installed and maintained correctly, these systems will give many years of reliable Internal Floating Roof/Covered Floating Roof service. The foam system can be used for fire Storage Tank is a combination of both the cone prevention, control or direct extinguishment of any roof and the open top-floating roof tank? The tank flammable or combustible liquid fire within the tank. has a cone roof but with the addition of an internal floating roof or pan that floats directly on the fuel To select the correct foam system, it is necessary surface. The open vents in the tank sidewalls just to understand the following systems: beneath the roof joint can identify this type of tank. Fixed System is a complete installation piped from If the internal floating roof is other than a steel a central foam station, discharging through fixed double deck or pontoon type, the fire protection discharge devices on the hazard being protected? system should be designed for full surface fires Foam proportioning components are permanently (similar to cone roof tanks). For the double deck or installed. pontoon internal roofs of steel construction, a design for sealed area protection may be permitted Semi Fixed System is an installation where the (same as open floating roof tanks). hazard is equipped with fixed discharge device(s), which connect to piping that terminates a safe Small quantities of flammable liquids are sometimes distance from the hazard, normally outside the dike stored in horizontal style tanks, which normally sit wall. Foam producing materials are transported to on saddles or in underground storage facilities. This the scene after the fire starts and are connected to section applies only to the three major types of the piping. tanks as listed above. CHEMGUARD 204 S. 6th Ave • Mansfield, Tx 76063 • (817) 473-9964 • FAX (817) 473-0606 www.chemguard.com DATA SHEET #D10D03190 REVISON: 09/2005 IDENTIFY THE FLAMMABLE LIQUID FIRE PROTECTION OF STORAGE TANKS There are two basic classifications of flammable U.L. has established two different types of foam and combustible liquids: discharge outlets: • Hydrocarbon (non water miscible) • Polar Solvent (water miscible) Type II Discharge Outlet - A fixed device that delivers foam onto the burning liquid and partially Hydrocarbons include non water-soluble petroleum submerges the foam and produces restricted liquids such as crude oil, gasoline, jet fuels, fuel agitation of the surface. Examples of this type of oils, etc. Polar solvents include water soluble device are Foam Chambers and Foam Makers. liquids such as alcohols, ketones, esters etc. Type III Discharge Outlet - A fixed or portable All Chemguard U.L. Listed and standard grade device that delivers foam in a manner that causes foam concentrates are suitable for use on the foam to fall directly onto the surface of the hydrocarbon fuel fires or spills. Only Chemguard burning liquid in such a way that causes general U.L. Listed and standard grade alcohol resistant agitation. Examples of this type of device are Hose AR-AFFF concentrates are suitable for use on polar Stream Nozzles and Monitors. solvent fuel fires or spills. Two basic methods of fire protection systems for NOTE: Pure MTBE is only slightly water miscible storage tanks: (approx. 4% - 6%). • Sub-surface Base Injection • Over the Top - (Subdivided as follows) Foam FLAMMABLE AND COMBUSTIBLE LIQUIDS Chambers, Foam Makers, Portable Foam PER NFPA 30 Monitors and Foam Tower Flammable Liquid means liquid having a flash SUB-SURFACE BASE INJECTION point below 100ºF (37.8ºC) and having a vapor pressure not exceeding 40 psi (276 kpa)(absolute) The sub-surface method of fire protection produces at 100ºF (37.8ºC) shall be known as a Class I liquid. foam with a HBPFM located outside the storage Class I liquids shall be subdivided as follows: tank. This system delivers the expanded foam mass through piping into the base of the tank. The • Class IA includes those having flash points pipe may be an existing product line or can be a below 73ºF (22.8ºC) and having a boiling point dedicated fire protection foam line. The expanded below 100ºF (37.8ºC). foam entering the tank through a discharge outlet is injected into the flammable liquid. The discharge • Class IB includes those having flash points outlet must be a minimum of 1 ft. above any water below 73ºF (22.8ºC) and having a boiling point that may be present at the base of the tank. The above 100ºF (37.8ºC). foam will be destroyed if injected into the water layer. When injected into the fuel, the foam will rise • Class IC includes those having flash points at or through the fuel and form a vapor tight foam blanket above 73ºF (22.8ºC) and below 100ºF (37.8ºC). on the fuel surface. Combustible Liquid means liquid having a flash Advantages of Sub-Surface point at or above 100ºF (37.8ºC). Combustible liquids shall be subdivided as follows: • The rising foam can cause the fuel in the tank to circulate which can assist in cooling the fuel at • Class II includes liquids with having flash points the surface. at or above 100ºF (37.8ºC) and below 140ºF (60ºC). • If there is an explosion and fire that could damage the top of the tank, the sub-surface • Class IIIA includes liquids with a flash points at injection system is not likely to suffer damage or above 140ºF (60ºC) and below 200ºF (93.3ºC). • The discharging foam is more efficiently • Class IIIB includes liquids with having flash directed to the fuel surface without any points at or above 200ºF (93.3ºC). interruption from the thermal updraft of the fire. CHEMGUARD 204 S. 6th Ave • Mansfield, Tx 76063 • (817) 473-9964 • FAX (817) 473-0606 www.chemguard.com DATA SHEET #D10D03190 REVISON: 09/2005 Disadvantages of Sub-Surface FOAM CHAMBERS (TYPE II DISCHARGE DEVICE) • CANNOT be used in storage tanks containing The Foam Chamber is normally used on cone roof polar solvent type fuels or products that require storage tanks. The chamber is bolted or welded on the use of AR-AFFF type foam concentrates the outside of the tank shell near the roof joint. A • Not recommended for use in either Floating deflector is mounted on the inside of the tank so Roof or Internal Floating Roof type tanks. that the discharging foam from the foam chamber will be diverted back against the inside of the tank • Caution must be used so that the maximum wall. foam inlet velocity is not exceeded; otherwise, excessive fuel pickup by the foam as it enters The foam chamber is mounted on the cone roof the tank will be experienced. storage tank wall shell in a vertical position just below the roof joint, or approximately 8" to 12" • Not to be used for protection of Class 1A down from the roof joint to the center point of the hydrocarbon liquids foam chamber outlet. In sequence Chemguard Models FC 2.5, 3, 4 and 6 foam chambers are to be mounted from approx. 8" to approx. 12” down from HIGH BACK PRESSURE FOAM MAKER the roof joint. When the foam chamber is mounted correctly, the internal glass seal of the chamber will The HBPFM device is mounted in the foam line be just slightly higher in elevation than the roof joint used to aspirate the foam solution before it is on the storage tank.