800 - fire and safety design

800 Fire and Safety Design

AbstractThis section contains guidance and requirements for tank and tank field design which reduce the risk of fire and improve the ability to fight a fire. It presents infor-mation on tank spacing, drainage, and impoundage and helps you determine the need for, and design of, fixed extinguishing systems. It also lists design consider-ations and methods that reduce the risk of fire. Both designer and management can use the section to determine design criteria beyond national, state and local codes and regulations.

Contents Page

810 General Considerations 800-2

811 Typical Causes of Fire

812 Design Considerations for Firefighting

813 Fire Protection

820 Location and Spacing 800-10

821 Location

822 Tank Spacing

830 Fire Suppression Systems 800-16

831 Risk Factors

832 Fire Water Systems

833 Foam Systems

840 Electrical Area Classification 800-27

850 Drainage and Impounding 800-27

851 Drainage

852 Remote Impounding

853 Diked Enclosures

July 2000 © 2000 Chevron USA Inc. All rights reserved. 800-1

800 Fire and Safety Design Tank Manual

810 General ConsiderationsTank fires occur at a rate of around 3 x 10-3 fires per tank year (or three fires per year for every thousand tanks). Compared to other types of equipment in the oil and chemical industries, this is a relatively low frequency. On the other hand, tank fires, when they occur, can be very spectacular, attract plenty of unwanted attention, and can be very costly. Therefore, a well-thought out balance of prevention, suppression and acceptable level of risk is the recommended approach to fire protection on tanks.

Overall, the design concepts for protecting tankage from fires are based on the following objectives:

1. Minimize the occurrence of tank fires.

2. Avoid conditions that can result in major spills, major vapor releases, froth-overs, or boilovers.

3. Contain spills, leaks, or overfills to minimize their effect on other tanks and associated equipment.

4. Control fires at the tank and limit their spread to other tanks or facilities.

811 Typical Causes of FireKnowing the cause of past tank fires helps us prevent future fires. Some common causes of tank fires and methods to prevent them are given below:

Lightning IgnitionSee Section 430 for a discussion of tank grounding.

Seals on Open-top Floating Roof Tanks. Prevent these fires by properly designing and maintaining shunts for primary and secondary seals, and insulated pantograph hanger sections where applicable. (See Section 420.)

Internal Floating Roof Tanks. Ignition has occurred at vent openings due to flam-mable vapors in the vapor space. The flammable vapor space can be caused by:

• A sunken roof• Filling the tank after the roof has been set on its legs• Volatile liquids entering the tank due to process upset• A separated roof seal

Use of a buoyant roof, routine monitoring of the vapor space, and procedural control during lightning storms will prevent such fires (see Section 420). Internal floating roofs are not vulnerable to lightning ignitions at the seals, and shunts are not required.

Cone Roof Tanks. On tanks with flammable vapor space, ignition has occurred when there have been openings through the roof. To prevent these incidents, use pressure/vacuum valves on the tank vents (see Section 743), assure the gaging and sampling hatches have been closed, and use proper maintenance to ensure that no

800-2 © 2000 Chevron USA Inc. All rights reserved. July 2000

Tank Manual 800 Fire and Safety Design

corrosion openings exist in the tank’s vapor space. It is recommended to use floating roof or internal floating roof tanks for flammable liquids and for liquids stored at or above their flash point (with the exception of hot asphalt tanks).

Overfill of Tanks Storing Flammable LiquidOverfilling can cause vapors to reach ignition sources outside the diked area (see Exterior Ignition Sources below). Overfills are prevented by sound operating proce-dures and controls. Engineering can assist by providing necessary gaging equip-ment, level alarms and shutdown equipment to carry out these procedures. This equipment should be designed and installed so that it is easy for the operator to test and maintain it. (See Section 900.)

Ignition While Performing Hot WorkPrevent these fires by detailed preplanning to identify and avoid potential risks when removing tanks from service and during maintenance work. Engineering can reduce risks during these operations by: (1) providing liquid-tight pontoon compart-ments (See Section 420) and (2) designing internal piping and structural members with positive drainage to minimize risk of flammable liquids being trapped (See Section 700.)

Hot Asphalt Tank FiresThese fires are caused mostly by cracking and rapid oxidation at excessively high temperatures. They primarily are prevented by operational control keeping storage temperatures below 400°F. Suitable temperature indicators and alarms must be provided. An alternate approach is to use inert blanketing for hot tanks.

Large Vapor ReleasesThese releases result from stocks with excessively high vapor pressure (over 14.7 psia true vapor pressure) entering atmospheric tankage. External sources have provided the source of ignition (see External Ignition Sources below). Suitable instrumentation on process equipment and in gasoline blending systems will mini-mize the release potential. Large vapor releases also have occurred from slop tanks where naphtha-type slops have been introduced into heated slop tanks. Segregated piping and tankage should be provided to avoid mixing light and heated heavy slops.

Tank Froth-oversFroth-overs occur when water enters hot tanks (over 212°F) or when hot streams enter tanks with water bottoms. The resulting massive froth releases have travelled significant distances to reach exterior ignition sources (see below).

Tank froth-overs can be minimized by (1) designing process limit cooling water systems to operate at a lower pressure than the hot process streams. This method prevents water from leaking through the cooler bundles into hot rundown streams; (2) providing proper instrumentation on rundown lines to tankage operating below 212°F, preventing these rundown streams from exceeding that temperature (usually 200°F is the tank temperature limit, see Section 1230); and (3) by designing facili-



ties to make it easy to regularly remove any water which accumulates in the bottom of the tank.

Pyrophoric IgnitionsThese spontaneous ignitions occur when iron sulfide deposits oxidize in the pres-ence of a flammable mixture in the vapor space of tanks. Such iron sulfide deposits can form on metal in the vapor space where the hydrogen sulfide content is high and there is no oxygen. Upon introduction of air, such deposits oxidize and create an ignition source.

During normal operation of sour stock tanks, the risk can be minimized by using floating roof tanks or by inert blanketing of fixed roof tanks. When removing sour tanks from service, use careful procedural control until the tanks are gas free and all built up deposits removed. Tank design should provide a means to evacuate gas and sweeten the tank.

Static Electricity IgnitionsSuch ignitions usually occur during initial filling, mixing, sampling, and gaging in fixed roof tanks. Refined stocks with conductivities lower than 50 picoSie-mens/meter (pS/M), and which can have flammable mixtures near the liquid surface are particularly vulnerable. The use of floating roof tanks in these services, with roofs properly bonded to the shell (see Standard Drawing GB-D1082 for bonding details) basically eliminates these potentials except during the initial fill period until the roof is floating.

Higher flash stock tanks, where hydrogen or light hydrocarbon vapors can enter with rundown streams due to process upsets, are also vulnerable. Some preventive steps which can be taken are:

Floating Roof Tanks:

• Fill the tanks with water until the roof is floating before you introduce the product, or

• Until roof is floating during initial fill, reduce fill rate to less than 3 ft/sec through inlet diffuser.

• Make the vapor space beneath the roof inert before filling.

Fixed Roof Tanks (handling refined stocks which can have flammable mixtures near the liquid surface):

• During initial fill, reduce the fill rate to less than 3 ft/sec through inlet diffuser until diffuser is covered by 6" of product.

• Provide gaging and sampling wells or

• Provide blanketing in the vapor space (could be inert, N2 flue gas, or natural or refinery gas).



Contaminated High Flash Stock Tanks:

• Closely control process operations, particularly stripping, to minimize carry-over of hydrogen or light hydrocarbon into tanks.

• Regularly sample rundown streams and test for product contamination.

• Periodically test vapor space of these rundown tanks to determine if flamma-bility exists.

• Provide gaging and sampling wells in these fixed roof tanks.

Exterior Ignition SourcesSources such as motor vehicles, energized electrical equipment, hot surfaces from pump bearing failure, and open flames can start fires. These ignitions usually occur with high vapor releases caused by overfilling or high-vapor-pressure stocks entering tanks. A similar problem exists when froth-overs occur.

Within the immediate vicinity of the tanks and their associated impounding and drainage areas, control is accomplished through proper electrical area classification and work permit procedures. It is impractical to protect against ignition for the major release situations. They are avoided through process controls, safe operating procedures, and training.

Equipment with a higher fire risk, especially pumps, should be located outside of tank impounds.

812 Design Considerations for FirefightingThe design must provide for containment of the tank contents and for the safety and effectiveness of firefighters during a tank fire. The basic fire protection design concepts for tankage areas require the movement of personnel, foam generating equipment, and portable hoses and equipment to the fire area. It is important to consult with the local fire fighting agency on available equipment and fire fighting techniques during the design phase. See Section 830 for a discussion of tank fire fighting.

AccessibilityAccessibility is the key factor, both in the movement of the mobile equipment to the fire site and the effective, safe use there. Some of the primary overall consider-ations in this regard are:

Roads. Two or more road accesses from different directions should be available to each tank field area. A road should be provided on at least one side of all low flash stock tanks. The roads must be wide enough or have sufficient turnouts to allow efficient maneuvering of firefighting vehicles.

Mains, hydrants. Fire water mains and hydrants should be located along these roadways, with hydrants positioned on the roadside of any dikes, pipeways, drainage ditches, or other obstructions. As appropriate, walkways or accessways



should be provided over wide pipeways or other obstructions to allow for running hose lines into the tankage areas.

Dikes. Dike heights normally should be limited to six feet above the surrounding land to allow ease of access over the dikes by firefighters. Stairways or other oper-ator accessways normally would be provided over both sides of the dike near the roadside for operations control.

Stairways. The bottom of the tank stairway should be located on the tank near the operator access point. For operation as well as firefighting considerations, locate the top of the stairway on the prevailing upwind side of the tanks where practical. Where dikes must be higher than six feet for earthen construction or four feet for concrete, an additional stairway on the opposite side of the dike enclosure is desir-able for easy egress.

Some specific design considerations for different types of anticipated fires are:

Seal Fires in Open-top Floating Roof Tanks• For larger tanks (greater than 120-foot diameter), handrails on wind girders for

emergency access around the tank, and foam dams on the roof, are required. The wind girder walkway can also be used for seal inspections.

• Foam dams as shown in Figures 800-6 and 800-7 are also required, although it is recognized they may present a hindrance to maintenance work.

• Firefighters need good access to the tank stairway for ascent to the roof platform.

Cone Roof Tank Vent Fires• Firefighters must carry portable equipment to the roof and need a minimum

stairway width of 30 inches.

• Locate the vents near the roof apex, or provide handrails in areas where vents are located near the roof edge.

Water Drawoff Fires• Sumps, under drawoff connections, should be connected to a closed drain

system to limit the area of any spill fires associated with these connections. The drain line should contain a liquid seal to prevent vapor and fire transmission into and/or from the sewer system.

• The drawoff connection should be located at least 15 feet from the main tank valve manifold to avoid manifold involvement in case of a drawoff fire. Where water drawoff lines are connected to the suction or fill lines, an additional valve should be provided at the suction or fill line connection to allow isolation in the event of a fire.

• In case of leakage and fire around the manifold area, the drawoff connection can be used for injecting water into the bottom of the tank.



Spill Fire/Impounding Basin Fire/Tank OverfillFirefighters need access to inside of diked areas to:

• Deliver foam by portable hose streams to cover small spill fires.

• Deliver water to cool exposed downwind tanks.

Drainage design is important to minimize exposure from spills to other tanks, piping, or other facilities. Remote impounding to contain the fuel carried away from tanks and piping is good fire protection design practice.

Fully Involved Tank Fire• Firefighters need access to diked areas to cool shells of downwind-exposed

equipment.

Crude Tank Fires with Boilover Potential• Store crude in floating roof tanks to avoid boilover potential. Experience also

indicates that boilover during fires in small crude tanks is not likely.

• If a cone roof crude tank fire should occur and boilover results, firefighters must evacuate the immediate area during that occurrence and then return to handle wide area spill fires. Overall layout should provide for such evacuation and subsequent access needs.

Many of the designs in the sections on drainage, layout, spacing and fire suppres-sion systems improve the effectiveness of firefighting efforts and minimize the spread of fire.

Fire Protection RequirementsInherently, many of the features of tank design and construction are related to mini-mizing fire losses. The welding and tank foundation requirements are designed to provide basic integrity to the tank. The steel materials of tank construction as well as the valve connections provide for high resistance under fire exposure. The spacing and layout requirements as well as drainage and impounding provisions are tied directly to fire containment and control. All such items cannot be included, but several key considerations are listed for emphasis. Reference should be made to the appropriate sections elsewhere in the Tank Manual for details relative to their design and installation.

General Design Requirements.

• High-level alarm(s) for protection against tank overfilling (see Section 900). These can be an important backup for operator control during tank filling.

• Acceptable types of fire resistant valves for connections below the liquid surface and in drainage and impounding areas (see Section 850). Suitable valve materials (normally steel) are necessary to avoid failure under fire exposure and additional liquid release to the fire. Also, valve closure might be required after fire exposure to stop fuel release. Specifically, no brass or bronze valves and no



wafer butterfly valves with exposed bolts should be used on the tank and in the drainage and impounding areas.

• Acceptable design arrangements for piping flexibility near tanks including fire resistance and mechanical flexibility (see Section 700). To avoid failures or leakage, piping must be flexible enough to accommodate settling of tanks, shifting of foundation, expansion and contraction from temperature changes and soil movement. If mechanical joints are used, they should not fail during fire exposure.

• Tank sampling connections, where installed below the liquid level, should have a root valve against the tank (normally closed except when sampling), readily accessible by the operators. For tanks with circular stairways, these valves should be accessible from the stairway or at a centrally located manifold (see Section 700).

• Drains for spill pads under sample connections or mixers should be tied to the area drain system through a sealed connection. This reduces the build-up of spilled oil which creates housekeeping and fire risk problems.

• Tank nozzles for filling/withdrawal, water drawoff, and sampling should not be installed beneath the stairway. This protects stairway access if a spill from one of these nozzles should catch fire. Also, these nozzles should be separated from each other (see Section 600).

Safe PracticesIn addition, there are a number of safety/fire prevention practices associated with tank maintenance and operations. Items falling into this category are:

• Safe operating practices to prevent overfilling tanks. Clearly developed and enforced procedures are essential in establishing firm operator control to avoid overfilling.

• Procedures and controls for filling, sampling and gauging. Static can accumu-late during filling, and restraints must be imposed during initial filling and during sampling and gauging of certain types of tanks to avoid introduction of an ignition source. Refer to API Recommended Practice 2003, “Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents.”

• Procedures for drawing water and minimizing oil losses which include oper-ator coverage at all times. Properly controlled water drawoff reduces the chance of significant oil spills and resultant potential for fire.

• Hot work on tanks in or out of service. Special precautions and procedures need to be established to properly eliminate or control ignitable materials at tanks where mechanical hot work is to be performed. Refer to Section 1100.

• Procedures for in-service testing and maintenance of level and alarm systems. Such instrumentation must be regularly tested to assure continued reliability. Testing must include the entire system — from primary level sensing element to the alarm in the control room. Where tanks must be removed from service



for necessary testing or maintenance, there is risk of continuing operation of tanks without workable level control instrumentation. Refer to Section 900.

• Maintenance procedures for gas testing and entering tanks. Carefully devel-oped cleaning, gas freeing, and gas testing procedures are essential to assure safety of personnel entering or working on tanks, both from a fire risk and toxic exposure standpoint. These procedures will vary based on tank type and mate-rial previously stored. Refer to Section 1100.

• Provisions for gas testing of floating roof pontoon compartments. Liquid or vapor leakage into pontoons can occur from inadequate top seam welding, improperly sealed manway covers, or corrosion. Before hot work can be started in these areas, there must be assurance that flammable or combustible mate-rials are not present. Refer to Section 1100.

• Provision for draining internal piping and structural supports when gas freeing before mechanical work. An overlooked accumulation of hydrocarbons in internal piping or supports can create a potential fire hazard.

• Provision for draining or pumping into or out of a tank during a fire. In certain tank fire situations, this may be the best approach to minimize losses. It should be considered in the emergency planning.

• Labeling is required on tanks in certain locations, based on legal or local requirements, to identify contents which may be flammable, combustible, or toxic. Refer to NFPA 704.

Requirements for Nonmetallic and Special Service TanksNonmetallic tanks or tanks in special services require procedures or design consid-erations:

• Use of nonmetallic tanks is limited generally to services where flammable materials are not being handled or to remote producing areas where failure or loss would be an acceptable risk.

• Plastic tanks should be protected from lightning and static ignition, if flam-mable vapors can occur. Lightning protection can be provided by lightning rods, conducting masts, or overhead ground wires. For details, see NFPA 78. Static electricity may be a problem for plastic tanks holding conducting as well as non-conducting fluids. All metallic objects such as manway openings, fluid connections, or gauging instruments, even if not in contact with the liquid, must be bonded together and grounded. Avoid having any metal projections inside the tank that create a spark gap with a rising liquid level. These projections provide a focal point for sparking from the liquid surface.

• Internal coatings, such as plastic or paint, <80 mil (2mm) thick in metal tanks do not create any added static hazard. Their resistivities are of the same order of magnitude as the oil, and they create no barrier to the flow of static charge.

• Special requirements for hot tanks. Controls must be established to prevent water entering or developing in such tanks to avoid steam formation and



resulting froth-over. Tank temperatures should be maintained above 250°F for this purpose. To avoid potential for self-igniting oxidation, maximum tempera-tures should be 400°F unless the tank is blanketed.

• Special requirements for slop tanks. In general, light and heated heavy slops should be segregated in separate systems to avoid significant vapor generation when light hydrocarbon enters a heated tank.

• Vapor recovery systems require special design based on many factors including layout, type and size of tankage, and hydrocarbons involved. The overall arrangement should not permit flammable mixtures to be drawn through compressors or long runs of piping.

813 Fire ProtectionWhile requirements may vary from state to state, all states incorporate, either wholly or in part, the fire codes developed by the National Fire Protection Associa-tion (NFPA) or the International Conference of Building Officials. NFPA’s Code 30 is the most widely used fire code in the U.S. Provisions of the code apply to many aspects of aboveground storage including design and construction of tanks, loca-tion, spacing, venting and spillage control, and protection of adjoining property or waterways by means of draining or diking.

The Uniform Fire Code, published by the International Conference of Building Officials, is adopted by seven western states. The requirements of the Uniform Fire Code are similar to those of NFPA.

820 Location and Spacing

821 LocationTank location is influenced by a number of factors including:

• Operating requirements,• Topographical features,• Fire protection considerations, and• Optimum use of property.

Operating RequirementsOperating requirements may dictate whether tankage is located close to or remote from units which they serve. Generally tanks are uphill from their transfer pumps and close to each other for ready access, short suction lines and minimum piping. Sometimes stock characteristics, quality control, or other factors may require loca-tion of tanks close to processing units. Generally these tanks should be limited in size to meet processing needs rather than storage requirements.



Topographical Features and Fire ProtectionThe surrounding topography should be used to the best advantage to suit immediate operating needs and to allow for expansion. Elevation, drainage, grading and exca-vation costs, and soil characteristics need to be considered.

Drainage is of prime importance in tank field layouts, and should be considered during initial designs rather than as a design detail after the layout is established. Making plot plans showing existing, new and future tankage is always helpful. Spills must be drained away from tanks and contained in remote impounds on Company property. Also spills should not endanger other Company facilities, including pumps, filters, major valve manifolds, major electrical equipment, or other equipment which may be located in the tank field.

Differences in elevation should be used in meeting drainage requirements. From a fire prevention standpoint, these considerations become even more important when handling flammable liquids with flash points below 100°F. For such low flash stock, including crude oil, avoid locating impounding and drainage areas at higher eleva-tions than other facilities. This is especially true for public roads and other offsite facilities, and in-plant facilities where personnel or equipment exposures might be involved.

Adequate roads are needed to provide ready access to all tanks and should be considered in the layout. These roads may be narrow, but they should be all-weather roads and provided with turnouts at convenient intervals to accommodate multiple vehicles involved in handing any emergency. There must be access so that tank field operators can conveniently reach each tank without taking a motor vehicle into an impounding basin area or across an open drainage channel that could contain flam-mable liquid.

Optimum Use of PropertyLocate tanks so that Company property is used to its maximum potential value as plant and building sites. Tanks should be located so they are in harmony with the planned development, or primary function, of the overall area. Consider aesthetics when locating a tank; especially if the tank can be seen from public accessways or if it changes the skyline. Also consider locating tanks away from easy public access and away from sources of fire outside the fenceline.

822 Tank Spacing

RegulationsTank spacing requirements are based on standards in the National Fire Protection Association’s Flammable and Combustible Liquids Code (NFPA 30). Company standards have been developed by the ETC Fire and Process Safety Team. These standards for proximity of tanks to property lines are the same as the NFPA 30 Code (1996 Edition). Shell-to-shell spacing is also the same as NFPA 30. This section gives minimum layout requirements under normal situations. Greater spacing should be considered where possible. The greater the spacing, the less likely other equipment would be damaged as a result of a nearby fire.



Distance from Property Lines and Public WaysRequirements for the location of aboveground tankage with respect to property lines and public ways are based upon the following criteria:

• Pressure limitation under emergency venting conditions,• Type of liquid stored and its behavior under fire conditions,• Type of tank, and the type of fire protection available.

Use Figures 800-1 through 800-4 to calculate distances. These figures give minimum standards which are acceptable under normal conditions. However, consider what is adjacent to the Company’s property line. Major high volume high-ways and buildings of high occupancy, may be at risk or be a source of high risk to Company facilities. In those cases, additional spacings should be considered. Alter-natively, use of the area nearer the property line for finished product tanks containing stocks with flash points above 140°F would minimize risk.

Fig. 800-1 Aboveground Tanks for Stable Flammable and Combustible Liquids (Below 200°F Flash Point) Other Than Crude Oil Reprinted with permission from NFPA 30-1996, “Flammable and Combustible Liquids Code”, Copyright © 1996, National Fire Protection Association, Quincy MA 02269. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.

Type of Tank Level of Protection

Minimum Distance in Feet from Property Line Which Is or Can be Built Upon, Including the Opposite Side of a Public Way (Not Less Than 5 Feet)

Minimum Distance in Feet from Nearest Side of Any Public Way or from Nearest Important Building on the Same Property (Not Less Than 5 Feet)

Floating Roof(1) Protection for Exposures(2) 1/2 times diameter of tank 1/6 times diameter of tank

None(3) Diameter of tank but need not exceed 175 feet

1/6 times diameter of tank

Fixed Roof Vertical with Frangible Joint for Roof-to-Shell Seam(1)

Approved foam or inerting system on tanks not exceeding 150 feet in diameter(4)

1/2 times diameter of tank 1/6 times diameter of tank

Protection for Exposures(2) Diameter of tank 1/3 times diameter of tank

None(4) 2 times diameter of tank but need not exceed 350 feet


Fixed Roof Horizontal and Vertical with Emer-gency Relief Venting to Limit Pressures to 2.5 psig

Approved inerting system on the tank or approved foam system on vertical tanks

1/2 times Figure 800-3 1/2 times Figure 800-3

Protection for Exposures(2) Figure 800-3 Figure 800-3

None(3) 2 times Figure 800-3 Figure 800-3

(1) Approved floating roof and frangible joint designs are defined in Section 420. (2) Protection for exposures means fire protection for structures on property adjacent to liquid storage. Fire protection for such

structures shall be acceptable when located (1) within the jurisdiction of any public fire department or (2) adjacent to plants having private fire brigades capable of providing cooling water streams on structures on property adjacent to liquid storage.

(3) Use this for producing areas where no fire water is on site and there is no public or private fire brigade to respond(4) For tanks over 150 feet in diameter use “Protection for Exposures” or “None,” as applicable.



Fig. 800-2 Aboveground Tanks for Class III B Liquids with Flash Points at or above 200°F Reprinted with permission from NFPA 30-1996, “Flammable and Combustible Liquids Code”, Copyright © 1996, National Fire Protec-tion Association, Quincy MA 02269.

Tank Capacity (Gallons)

Minimum Distance in Feet from Prop-erty Line Which Is or Can be Built Upon Including the Opposite Side of a Public Way

Minimum Distance in Feet from Nearest Side of Any Public Way or from Nearest Important Building on the Same Property

12,000 or less 5 5

12,001 to 30,000 10 5

30,001 to 50,000 10 10

50,001 to 100,000 15 10

100,001 or more 15 15

Fig. 800-3 Reference Minimum Distance for Use in Figure 800-1 Reprinted with permission from NFPA 30-1996, “Flam-mable and Combustible Liquids Code”, Copyright © 1996, National Fire Protection Association, Quincy MA 02269.

Tank Capacity (Gallons)

Minimum Distance in Feet from Prop-erty Line Which Is or Canbe Built Upon Including theOpposite Side of a Public Way

Minimum Distance in Feet from Nearest Side of Any Public Wayor from Nearest ImportantBuilding on the Same Property

275 or less 5 5

276 to 750 10 5

751 to 12,000 15 5

12,001 to 30,000 20 5

30,001 to 50,000 30 10

50,001 to 100,000 50 15

100,001 to 500,000 80 25

500,001 to 1,000,000 100 35

1,000,001 to 2,000,000 135 45

2,000,001 to 3,000,000 165 55

3,000,001 or more 175 60



Shell-To-Shell SpacingIt is generally Company practice to follow NFPA 30 Code requirements for minimum spacing between aboveground storage tanks. However, for large tanks having diameters over 120 feet but less than 150 feet, and for smaller fixed roof crude oil tanks in remote locations having remote impounding, Company shell-to-shell spacing requirements are more conservative than NFPA 30. Greater spacing will allow for adequate drainage of spilled oil away from tanks, limit the chance of spread of a large tank fire and provide better access for handling fires in these large tanks.

Figure 800-5 gives the Company’s spacing requirements. In the figure, D1 and D2 are the diameters of any two adjacent tanks.

Fig. 800-4 Aboveground Tanks for Crude Oil Reprinted with permission from NFPA 30-1996, “Flammable and Combustible Liquids Code”, Copyright © 1996, National Fire Protection Association, Quincy MA 02269.

Type of Tank(1) Protection

Minimum Distance in Feet from Property Line Which Is or Can be Built Upon Including the Opposite Side of a Public Way (Not Less Than 5 Feet)

Minimum Distance in Feet from Nearest Side of Any Public Way or from Nearest Important Building on the Same Property (Not Less Than 5 Feet)

Floating Roof Protection for Exposures(2)

1/2 times diameter of tank 1/6 times diameter of tank

None(3) Diameter of tank 1/6 times diameter of tank

Fixed Roof(4)

Vertical With Frangible Joint for Roof-to-Shell Seam

Approved foam or inerting system

Diameter of tank 1/3 times diameter of tank

Protection for Exposures(2) 2 times diameter of tank 2/3 times diameter of tank

None(3) 4 times diameter of tank but need to exceed 350 feet


(1) Approved floating roof tanks and frangible joints are defined in Section 100 and API 650. (2) Protection for exposures shall mean fire protection for structures on property adjacent to liquid storage. Fire protection for

such structures shall be acceptable when located (1) within the jurisdiction of any public fire department or (2) adjacent to plants having private fire brigades capable of providing cooling water streams on structures on property adjacent to liquid storage.

(3) Use this for producing areas where no fire water is on site and there is no public or private fire brigade to respond.(4) It is NOT ALLOWED to store liquid with boilover characteristics (such as crude oil) in fixed roof tanks over 120 feet in

diameter. See the Fire Protection Manual.



Spacing from and in Operating FacilitiesAn operating facility is typically an area containing operating equipment such as furnaces, boilers, pumps, compressors, pressure vessels, separators, loading rack, etc. For convenience, pipeways and access roads normally separate operating facili-ties from tankage. The minimum recommended spacing requirements between tanks and other operating equipment including operating facilities are:

• A clear space of 100 feet from product tanks to an operating facility

• A clear space of 200 feet from crude tanks to an operating facility

• At least 200 feet from tank impoundment basins to flares (confirmed by radiant heat calculations)

• At least 75 feet from tanks to operations control buildings

• At least 200 feet from tanks to cooling towers

Fig. 800-5 Minimum Spacing (Shell-to-Shell) Between Aboveground Tanks for Flammable and Combustible Liquids Reprinted with permission from NFPA 30-1996, “Flammable and Combustible Liquids Code”, Copyright © 1996, National Fire Protection Association, Quincy MA 02269.

Floating Roof Tanks(1) Fixed Roof Tanks

For All Type Liquids Crude OilClass I & II (Other

Than Crude)(2) Class IIIA(2)

1. Tanks Not Over 120 Feet Diametera. For tanks having

remote impounding

b. For tanks not having remote impounding

Note(3)

Note(3)

2. Tanks Over 120 Feet Diametera. For tanks having

remote impounding

b. For tanks not having remote impounding

Note(4)

Note(4)

Note Tanks used for storing Class IIIB liquids may be spaced no less than 3 feet apart unless within a diked area or drainage path for a tank storing Class I or II liquid, in which case provisions of this figure apply.

(1) A floating roof tank is defined in Section 100. (2) Class I and II are liquids with flash point below 140°F. Class IIIA liquids are liquids with flash point at or above 140°F

but below 200°F. Class IIIB liquids are liquid with flash point at or above 200°F.(3) Crude oil tanks at production facilities in isolated locations having capacities not exceeding 126,000 gallons (3,000

barrels) need not be separated by more than 3 feet.(4) Crude oil storage in fixed roof tanks over 120 feet in diameter is not allowed. See the Fire Protection Manual.

D16

-------D26

-------+D16

-------D26

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-------D26

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-------D26

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D16

-------D26

-------+D14

-------D24

-------+D16

-------D26

-------+D16

-------D26

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D16

-------D26

-------+D14

-------D24

-------+D16

-------D26

-------+

D14

-------D24

-------+D13

-------D23

-------+D14

-------D24

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• At least 50 feet from small product tanks to drums, exchangers, loading racks and transformers

• Closer spacing may be adequate for small tanks in small plants

Other spacing requirements for producing tankage are given in the Fire Protection Manual. For marketing plants, loading racks should be spaced a minimum of 50 feet from high flash tankage (over 100°F flash point) and 100 feet for flammable liquid storage.

830 Fire Suppression SystemsThis section discusses fire risk, the Company’s resulting plan for suppressing fires in various areas, and specific design information for built-in water and foam systems. For more information, see the latest version of API 2021, Aboveground Storage Tank Firefighting.

831 Risk FactorsThe firefighting equipment provided for tankage areas varies significantly in the various parts of the Company, based both on economics and the risks involved. A number of risk factors must be considered:

• Tank sizes, storage volumes, and products being stored.

• Type of tankage (external or internal floating roof, or cone roof).

• Overall economic impact on Company operations in case of a fire loss in these facilities.

• Potential risk to non-Company properties in event of a tank fire.

• Potential for risk to Company tanks from adjacent operations or facilities.

• Chances for product contamination from unusual or upset operations.

• Availability of operations personnel and others to adequately mount a fire-fighting effort.

• Availability of outside fire brigades or other emergency assistance.

• Public relations aspects associated with prolonged tank fires.

• Tank fire history for specific geographic areas.

Resulting PlanThe Company has weighed these risks in light of its experience to decide which facilities will have built-in fire suppression systems. The normal approach that has evolved is:

Producing tankage normally would not be equipped with firefighting facilities. This is primarily due to the remote locations and absence of a local source of fire water.



Marketing bulk plants, terminals, and pipeline stations normally would not have built-in firefighting facilities. These areas typically depend on public fire brigades and their water supplies and equipment. In-plant firefighting facilities may be provided in certain areas of special exposure or reduced spacing, or where local codes and regulations require them to be installed.

Refineries and other manufacturing plants typically have built-in fire protection facilities for tankage areas along with their other operating areas. Foam is the primary extinguishing agent for tank fires, with water used to cool exposed tank shells. The assumption is that only one tank fire will occur at any one time, and the fire fighting system is sized accordingly.

Fire Suppression for Refineries and Other Manufacturing PlantsOverall design philosophies for fire suppression in tankage areas are given next. If the Company decides that other facilities, such as marketing terminals, need in-plant fire protection, the principles given here would need review individually before they are applied.

Open-Top Floating Roof Tanks. Provide sufficient foam to cover the rim space only. Depending on tank size, either portable hose streams or permanently attached equipment would deliver the foam.

Foam solutions would be proportioned on mobile foam trucks, with the water supplied from the fire water system. The fire water system would also need suffi-cient capacity to provide cooling water for exposed tank surfaces.

Cone Roof Tanks. It has been Company policy not to install permanently attached equipment unless required by local codes or ordinances. Any fire other than vent or spill fires would probably involve the entire surface area. Fires in tanks over 120 feet in diameter would be difficult to extinguish with any type of fixed fire suppression system. If portable devices could not deliver sufficient foam to the surface for extinguishment, fire fighters would then concentrate on cooling the shells of exposed tanks in the area. This cooling should focus primarily on the vapor space of these tanks.

Vent-type fires can readily be handled with portable equipment.

Internal Floating Roof Tanks. Similar to cone roof tanks, except full surface fires are not considered a likely scenario and any fire suppression equipment would be sized for a seal fire scenario.

Tankage Area Spill Fires. No special equipment is normally provided. The area’s fire water system and foam equipment on hand for other purposes can control such fires adequately.

832 Fire Water SystemsThis section covers sizing and location of fire water mains and location of hydrants within the tank field area. For design details of overall in-plant fire water systems, see the Fire Protection Manual.



Fire Main SizingThe Fire and Process Safety Team recommends sizing fire mains around tank fields for the largest of the following:

• water for making the amount of foam needed for a rim seal fire

and/or

• cooling of adjacent tanks in the event of a full surface fire in any one tank.

Full surface tank fires are very rare and, although this scenario should not be consid-ered when sizing fire mains, plans should be made on where water would be obtained if needed. The plan could include calling in outside resources and boosting water pressure from available public or private sources or drafting from streams or ponds. If a tank site is so remote as to preclude water being boosted to the site, consideration may be given to supplying a branch to the location.

For Foam Generation. Mains would supply enough water to make the amount of foam needed to handle a single rim space fire at any one time on any one open-top floating roof tank. (Rim area is assumed to be 2 feet wide.)

• With foam dams: 3.0 gpm per ten square feet of rim area• Without foam dams: 5.0 gpm per ten square feet of rim area

For Cooling the Tank. Additional water should be available to cool the tank shell surface above the level of the floating roof.

• 1.0 gpm per 10 square feet of the upper half of the tank shell for 50% of the periphery

For Cooling Adjacent Tanks. For cone roof tanks, internal floating roof tanks, and for the remote case where an open-top floating roof tank roof may be sunk, cooling water would be provided for a maximum of 3 adjacent tanks. (Adjacent tanks are those downwind of a burning tank within 1-1/2 tank diameters’ distance and within any one quadrant.) Application of water to these tanks will be by fire hose stream or portable monitors.

• 1.0 gpm per 10 square feet of vapor exposed surfaces, limited to upper half of shells and 50% of the periphery of one tank and 25% of periphery on each of the other tanks.

Fire Main LayoutLayout in the tankage areas would follow the normal looped arrangement with adequate valving to assure flow in case of fire main damage or failures. The normal looped arrangement is described in the Fire Protection Manual.

Hydrants In accordance with the Fire Protection Manual, hydrants should be:

• On the streetside or accesswayside of all pipelines, fences, dike walls or drainage ditches



• Near accessways or walkways which cross drainage ditches hindering access to the tankage

• Located so that all parts of every tank shell will be within reach of a stream from a hose no longer than 300 feet

• Positioned along the road near the point of normal access to the bottom of the stairway of open-top floating roof tanks

• Located within 100 feet of any foam lateral run to the road for connection to a mobile foam truck

833 Foam SystemsIt is Company policy to provide the capability to apply foam to fight rim space fires on open-top floating roof tanks as defined in Section 831. While roofs can sink, they sink so infrequently that it is not Company policy to provide foam protection for a total surface area fire.

This section covers foam attachments for open-top floating roof tanks. If, because of local regulations or other special reasons, foam protection is to be installed on cone roof or internal floating roof tanks, refer to NFPA 11 “Low Expansion Foam And Combined Agent Systems” for design details. Overall foam design information related to mobile vehicles, foam types and storage and portable equipment are covered in the Fire Protection Manual. Also see that manual for various approaches to fighting tank fires, including subsurface injection of foam through fill lines.

MaterialsHard-piped foam systems in salt water service have plugged from corrosion prod-ucts in a short time. For this service, piping should be epoxy-lined. Consult with the appropriate ETC specialist for an appropriate lining system.

Up to 120-foot-diameter TanksHose can be laid up the stairs to the gaging platform and foam directed by hand. If the hose won’t reach all the seal from the platform, it can usually be taken down the roof ladder, and, if necessary, onto the roof to extinguish any remaining fire at the tank seal. Foam dams are normally justified on these smaller floating roof tanks only in areas of high lightning frequency where tank appurtenances would interfere with applying foam to the entire seal space from the gaging platform.

Over 120-foot-diameter TanksBecause of their size, these tanks should have some semi-fixed or fixed facilities to make it easier to start firefighting and to handle hoses. These facilities are described below for various tank sizes. In addition, these large tanks should have the following: their wind girders should have a clear width of 24 inches or greater and handrails, so they can double as walkways; and a foam dam should be installed to contain any foam applied in the rim space area.



On 121- to 150-foot-diameter Tanks. Foam solution piping can be routed two ways. In the first way, a dry pipe riser is installed from ground level to a point just above the wind girder. The riser should end below the shell top angle and be acces-sible near the top of the stairway with two 2½-inch valved outlets, one of which should be equipped with a 1½-inch reducer for a 1½-inch fire hose. The clearance between valve handles and the wind girder handrail should be 24 inches.

Alternately, the foam solution piping can be routed beneath the wind girder (prop-erly braced) to provide the hose connections at the outer edge of the handrail. Depending on local conditions, this riser can start a few feet above ground level on the shell of the tank or be extended to the road where it can be reached without having to lay a hose to the tank (see Standard Drawing GC-S1005).

On 151- to 200-foot-diameter Tanks. These tanks should have two dry pipe risers: one located near the gaging platform and the other spaced about 180 degrees from it. The riser near the gaging platform should be fitted with a special foam maker assembly. Applying foam beneath the platform will enable firefighters to safely access the platform when they arrive and assess the best way to put out the fire.

Figure 800-6 shows the necessary appurtenances for the approach. The piping to the foam maker should have a valve in it so it can be shut off from the wind girder if the foam maker is not needed. The valve should normally be open so that if a seal fire should occur in the vicinity of the platform the foam will run down the inside of the shell and in to the seal space under the platform. This fixed foam maker should have a capacity of at least 50 gpm of water-foam concentrate solution.

Fig. 800-6 Dry Pipe Riser Installation for Floating Roof Tanks 151 to 200 feet in Diameter (Conceptual Layout Only)



Over 200-foot-diameter Tanks. Because of their size, these tanks should be equipped with permanently attached equipment for extinguishing fires in the seal space. Over-the-top foam application is the preferred approach for both reliability and cost. Figure 800-7 shows the conceptual layout for this system. Several other effective methods are commercially available and could possibly be used. The Fire Protection Staff should be consulted for details of design.

Over-the-top Foam Application

Header, Nozzles, and Splash Shield. This design consists of installing a properly sized piping header or ring main around the outside wall of the shell on or near the wind girder and connecting it to a series of foam makers, spaced at approximately 80-foot intervals, which discharge foam down the inside surface of the shell onto the floating roof seal. A single pipe riser supplies the header from a hose connec-tion near the bottom of the tank shell or from the access roadway. The seal space is filled rapidly with all foam makers being used simultaneously. The foam discharge nozzles must be high enough to be above the roof in its most extended position. This necessitates the installation of splash shields attached to the top angle of the tank which will direct the foam downward along the shell into the seal space. Piping design should provide for inlet pressure between 75 psi and 100 psi at the foam makers.

Fig. 800-7 Over-the-top Foam Application for Tanks Over 200 feet in Diameter (Conceptual Layout Only)

.



Hand-held Hose Lines. Two dry pipe risers should be installed per Standard Drawing GC-S1055: one located near the gaging platform above the wind girder and the other about 180 degrees across the tank. These risers allow firefighters to put out limited seal space fires with a hand-held hose from the wind girder without having to activate the entire built-in system.

High winds may also prevent complete fixed systems from blanketing all areas. Hand-held hose lines provide a ready means of covering these voids in the foam blanket.

Application Rate. The minimum design rate of solution for this system would be 3 gpm per 10 square foot of the seal area surface. Considering the maximum spacing of these foam makers around the seal area and the size of foam makers used (50 gpm at 75 psi inlet pressure), the actual rate would be in excess of 3 gpm per 10 square foot of seal area surface. A minimum supply of foam concentrate should be available to assure at least 20 minutes’ foam application at minimum rates for the largest tank involved.

Foam DamsThese dams retain the foam at the seal area and provide for sufficient depth to cause the foam to flow laterally to a point where the seal may have been ruptured. They also prevent excess foam from flowing out onto the roof. Foam dams are required for open-top floating roof tanks over 120 feet in diameter and for smaller tanks in high lightning areas.

Location: Two feet from the roof edge to minimize amount of foam required to cover the seal area.

Height: 2 feet minimum, with 6 inches elevation above the high point of weather shields, secondary seals, collection trough for wax scrapers, or any other appurte-nance that might interfere with applying foam to the seal area.

Material: At least No. 10 U.S. Standard Gage galvanized steel sheet securely fastened to the roof. No roof accessories such as vents or gage hatches should be between the dam and the shell.

Drain Slots: The dam should have slots to release rainwater but the size should be minimized to reduce the amount of foam lost during an emergency. Vertical slots, 1 inch high by ½ inch wide spaced at 10-foot intervals will normally be adequate. There should be no other openings on the bottom of the foam dam.

Attachment Method: The dam is to be attached to the roof by a 2" in 10" stitch weld or other means to avoid leakage except at drain holes.

Foam Solution PipingGalvanized pipe should be used in these systems. This piping, particularly where salt fire water is used, is very vulnerable to scale and rust formation, with conse-quential plugging of the small foam maker orifices. Periodic flow testing of these systems is essential (see Fire Protection Manual). After testing, the system should be fresh-water flushed.



Calculations to Establish Recommended Foam SuppliesFollowing are the formulas to calculate the amount of tank fire foam you need (see also Figure 800-8):

Tank Size.

• Tank diameter - (needed to calculate the surface area square feet)

• D2 × .785 = Surface area sq. ft. (needed to calculate the foam-water solution application rate

Topside/Full Involvement.

• .16 gpm × Surface Area Sq. Ft. = Foam-Water Solution application rate for tanks smaller than 150 ft. diameter.

• .20 gpm × Surface Area Sq. Ft. = Foam-Water Solution application rate for tanks 150 ft. diameter and larger.

• .03 (3%) × Foam-Water Solution gpm application rate = Concentrate gpm required.

Topside/Seal (6 in).

• D2 × .785 - ((D - 1)2 × .785) = Surface Area Sq. Ft.

• .3 gpm × Surface Area Sq. Ft. = Foam-Water Solution application rate.


• Concentrate gpm × 20 = Concentrate (gal.) required for a 20 min. application.

Topside/Seal (8 in).

• D2 × .785 - ((D - 1.33)2 × .785) = Surface Area Sq. Ft.




Subsurface Injection.


• .03 (3%) × Foam-Water Solution application rate = Concentrate gpm required.




July 2000©


F



840 Electrical Area ClassificationElectrical area classification of tank fields is detailed in the Electrical Manual, Section 300. Review this document when designing electrical equipment to go on tanks, in impounding areas, or near drainage ditches to impounding basins. Section 300 is based on the concepts presented in API Recommended Practice 500-B and -C for petroleum operations and NFPA 497 for chemical plants.

We classify areas to avoid fire potential during normal or reasonably anticipated upset conditions. The classification system is not intended to include catastrophic releases that are improbable with proper equipment design and reasonable operator control. All areas are classed in one of two divisions:

Division 1: Areas where flammable gases (flash point < 100°F) might be found under normal operating conditions.

These might include the interior of tanks handling flammable liquids, 5' area around pressure vents on cone roof tanks, and any sumps or below-ground pits in impounding basins where flammable liquids are handled.

Division 2: Areas where flammable gases might be found infrequently, such as during equipment failure or operator error.

This includes all areas 10' from tank, within impounding basins serving tanks handling flammable liquids up to the height of the dike, areas within the drainage paths to remote impounding, and a zone immediately adjacent to flammable liquid tanks.

Figures 800-9 and 800-10 provide the basis for classification around flammable storage tanks and in drainage paths to remote impounding basins.

850 Drainage and Impounding

851 DrainageProper drainage design is a major factor in meeting tankage safety objectives. Tank fields preferably should drain to a remote impounding area on Company property. This will prevent a spill from endangering adjoining property and waterways, and from exposing valuable Company property. This section is based on the standards in NFPA 30.

Drainage can be by large drain pipes or surface drainage but is usually provided by overland flow in shaped channels or swales. Surface drainage should slope away from tank piping and other equipment at a 1% minimum grade. This helps prevent underside corrosion and fire at the base of a tank. Surface drainage can use low diversion walls and/or drainage ditches or channels to divert the liquid to the impounding area. Where drainage channels go through pipes or culverts, a means should be provided to direct overflow in case of pipe plugging or flooding. This can usually be done by lowering a section of the elevated roadway or dike directly over the pipe or culvert.



Fig. 800-9 Flammable Liquid Storage Tank—Electrical Classification of Areas Courtesy of the American Petroleum Institute

Fig. 800-10 Drainage Path to Remote Impounding Basin from Flammable Liquid Storage Tank—Electrical Classifica-tion of Areas

Note 1: For floating roof tanks, the area above the tank roof and within the shell is classified Division 1.

Note 2: High filling rates or blending operations involving Class I liquids (<100°F flash point) may require extending the boundaries of classified areas.

Note 3: Distances given are for typical process areas and oil and gas handling facilities; they must be used with judgement, with considerations given to all factors discussed in Section 300 of the Electrical Manual.

Note: Distances are for typical process areas and oil and gas handling facilities; they must be used with judgement, with consideration given to all factors discussed in Section 300 of the Electrical Manual.



Drainage channels should be sized as a minimum to handle the largest stream of oil that could result from a tank overfill or discharge from a broken pipeline under maximum normal pump pressure or by gravity from one of the tanks. (Flow chan-nels and dikes are not usually designed for a tank rupture.) The other major consideration for drainage runoff would be rainfall and fire water. Some guidance on these quantities is given in Section 500 of the Civil and Structural Manual.

Rainwater from floating roof tanks should be directed into a drainage channel to the basin and not piped directly to public waters. This allows an easy visual check that the roof drain is functioning properly and prevents a spill from escaping into other areas that possibly do not have large enough retention capacity.

It is important to locate electrical equipment outside of electrically classified drainage areas (Section 840). It should also be located far enough away from liquid drainage and impounding areas so that it is unlikely to be damaged if a fire should involve the spilled liquid. Motor vehicle access for tank field operators should not cross impounding basins or drainage channels that could contain flammable liquids.

852 Remote ImpoundingRemote impounding basins are the preferred method of containing spills from tank fields. The impounding area should be designed to hold, at minimum, the contents of the largest tank in the tank field. At basin capacity, the impounded liquid should be at least 50 feet from the nearest tank or any property line that can be built on. Where remote impounding cannot be used to contain the total contents of a spill, partial remote impounding is more desirable than diking to impound all spilled liquid close to the tank and piping.

The basin should be sloped to drain to a low point where a drain pipe can release accumulated rainwater. There must be a valve on the drain line outside of the basin and it must be normally closed. The basin dikes are normally built of earth and should be shaped to be durable and be easy to maintain. The dike can have an access road on top but an access road at the outside base of the dike would be more useful in an emergency.

853 Diked EnclosuresWhere remote impounding cannot be used because of space or other limitations, diking around the tankage may have to be used. The grading in such enclosures should flow liquids away from tankage and piping at a 1% minimum grade to a low point within the enclosure. This point should be remote from the tankage and piping, where accumulated liquid can be drained or pumped out. This will tend to minimize potential fire exposure in case of a spill fire. Similarly the surface drainage within the enclosure should be arranged to quickly remove spilled hydro-carbons from under pipeways to minimize involvement of the piping in case of a spill fire. The outside base of the dike at ground level should be no closer than 10 feet to any property line that could be built on. The area between the dike and the fence should be kept clear for access.



Diked enclosures should be able to contain the greatest amount of liquid that can be released from the largest tank within the diked area. The capacity of the diked area enclosing more than one tank should be calculated by deducting the volume of the tanks other than the largest tank, below the height of the dike. However, if multiple small tanks in the area could be overturned or damaged during an earth-quake the diked area capacity should be greater than the capacity of the largest tank.

Dikes must be liquid-tight and impervious to the stock. They can be constructed of suitable earth, masonry, concrete, or metal depending upon the space available. Diked areas located in extremely porous soils may require special treatment to prevent seepage of hazardous liquids to low-lying areas in case of spills.

The average interior height of such dikes should not be more than six feet above grade. If higher dikes are needed due to local considerations, special added design features, such as remote operator valves, elevated walkways, or similar arrange-ments may be required (consult NFPA 30).

Each dike containing two or more tanks should be subdivided, preferably by drainage channels or at least by 18-inch high intermediate dikes, to prevent small spills from endangering adjacent tanks within the dike area. Again NFPA 30 can guide you on subdivision requirements.

In general, pumps, filters, and other equipment in the tank field, including major valve manifolds, should be located outside of the dike areas where they will not be affected by tank spills. In some cases it may not be feasible to protect this equip-ment from the maximum possible spill, but it should be protected from a spill of at least 10% of the largest tank in the impounding area.

Motor vehicle access for tank field operators would normally be excluded from the diked areas of flammable liquid tankage. However, access must be provided into these diked areas for maintenance equipment. This is usually accomplished by ramped entries into the diked area. Vehicles need hot work permits to enter tank diked areas.

Where provisions are made to drain water from the impounding area, a manual gate valve operable from outside the impound area should be provided. It must normally be closed.

Pipes Through Dike WallsOpenings where pipes pass through dikes must be carefully sealed. Also, the pipes should be installed in sleeves for protection and ease of maintenance. Richmond Refinery seals the annular space between the pipe and the sleeve with the T. D. Williams Link Seal system. All links can be sealed with Link Seal Model “LS” casing end seals. The inside diameter of the sleeve ends should be beveled to facili-tate installation of the link seal. Link seals can be ordered in accordance with the following designations:



Clean Water ActAboveground storage systems with a capacity of 660 gallons in a single tank, or 1320 gallons in aggregate, come under the Spill Prevention, Control and Counter-measure (SPCC) provision of the Clean Water Act if these facilities could reason-ably be expected to discharge oil into navigable waters. Regulated facilities are required to develop SPCC plans for the prevention and cleanup of oil spills, which must include a commitment of necessary manpower and materials.

The regulations issued under the act provide guidelines for the preparation and implementation of the SPCC plan. The plan is to be prepared in accordance with good engineering practices. It must have the full approval of management at a level of authority required to commit the resources needed for the plan’s implementation. Any additional facilities, procedures, methods, or equipment not yet fully opera-tional that the plan calls for are to be discussed separately. The plan should provide details on installation and operational startup.

For petroleum storage tanks, the plan must include the design and installation of a diked area capable of containing the contents of the largest tank plus any precipita-tion runoff, thus effectively preventing spills from reaching surface water. The plan also must include the training of personnel to detect and respond to spills. In addi-tion, a procedure must be set up to notify immediately the appropriate spill response agencies. Finally, the SPCC plan must be reviewed and certified by a registered professional engineer.

Federal OSHA RegulationsFederal OSHA regulation CFR 1910.106 covers the design, construction and opera-tion of tanks. The regulations also contain provisions requiring diking and impound-ment in areas surrounding aboveground tanks. API 650 and other API tank standards are adopted in OSHA regulations. Therefore, if tanks are built per API standards and the Company’s Safety in Designs Manual, compliance requirements will be satisfied.

Designation ServiceC Standard service -40°F to +250°F (insulating type)S Corrosive service -40°F to +250°FO Oil resistant service -40°F to +250°FT High temperature service 67°F to +450°FFD FS fire rated service (non-insulating)“Pyro-Pac” To be used on lines entering firewalls, impound areas,

and on angled entrance sleeves.


800 - fire and safety design

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