Mobil Egs 303 (1993) Recommended Spacing Within Operating Facilities

RECOMMENDED SPACING WITHIN OPERATING FACILITIES

FEBRUARY 1993 PAGE 1 OF 25 EGS 303 — 1993

TABLE OF CONTENTS

1. Scope 5.6 Control Houses and Operator Shelters2. Purpose 5.6.1 Central Control Houses3. References 5.6.2 Multi-Unit Control Houses4. Definitions 5.6.3 Process Unit Control Houses5. Spacing Recommendations 5.6.4 Operator Shelters

5.1 Application of the Guide 5.7 Satellite Instrument Houses (SIHs)5.2 General Requirements 5.7.1 Single-Unit Satellite Instrument

5.2.1 Terrain Houses (SIHs)5.2.2 Prevailing Wind 5.7.2 Multi-Unit Satellite Instrument5.2.3 Access for Fire Fighting and Houses (SIHs)

Maintenance 5.8 Electrical Substations5.2.4 Spacing to Public or Noncompany 5.8.1 Main Substations

Property 5.8.2 Process Unit Substations5.3 Emergency and Fire Fighting Equipment 5.8.3 Explosionproof Outdoor

5.3.1 Isolation Valves and Pipeways Electrical Switch Racks5.3.2 Water Spray Control Valves and 5.9 Utility Facilities

Emergency Shutdowns 5.9.1 Plant Air and Instrument Air5.3.3 Fire Hydrants and Monitors Compressors5.3.4 Fire Stations 5.9.2 Cooling Towers5.3.5 Fire Pumps 5.10 Offsite Tank Storage5.3.6 Spacing of Emergency Showers 5.10.1 Atmospheric Storage Tanks

and Eyewash Stations 5.10.2 High-Pressure Storage Tanks5.4 Buildings Outside Process Units 5.10.3 Refrigerated and Cryogenic5.5 Process Equipment and Unit Spacing Liquid Storage Tanks

5.5.1 Process Unit Spacing 5.11 Loading and Unloading Facilities5.5.2 Fired Heaters 5.11.1 Truck Loading Racks5.5.3 Pumps 5.11.2 Tank Car Loading Racks5.5.4 Gas Compressors/Expanders 5.11.3 Petroleum Piers and Wharves5.5.5 Cogeneration Facilities 5.12 Flares5.5.6 Heat Exchangers 5.13 Other Offsite Facilities5.5.7 Air Coolers Containing 5.13.1 Wastewater Separators

Hydrocarbons 5.13.2 TML and TEL Blending Plants5.5.8 Desalters 5.13.3 Blowdown Drums5.5.9 Towers and Vessels 5.13.4 Fire Training Areas5.5.10 Onsite Tanks 5.13.5 Compressed and Liquefied Gas5.5.11 Air Intakes Storage5.5.12 High Skin Temperature Equipment 5.13.6 Railroad Tracks5.5.13 Equipment Handling Non- 6. Process Equipment Spacing Tables

flammables, Noncombustibles, or Appendix — Evaluation Procedure forNontoxics Determining Alternative Spacing

Requirements

1. SCOPE

This Guide (formerly EGS 622) recommends minimum spacing for process equipment within the propertyboundaries for new or modified units. Access requirements for safety and fire fighting are also discussed.Appropriate requirements are provided for spacing between Mobil facilities and neighboring community areas

MOBIL ENGINEERING GUIDE

EGS 303 — 1993 PAGE 2 OF 25 FEBRUARY 1993

or other adjacent facilities. When the spacing recommended in this Guide is not achievable, considerationmay be given to the factors discussed in Paragraph 5.1. Local regulations, when they are more stringent,may take precedence over the provisions in the Guide.

2. PURPOSE

This Guide is intended for use in the design of operating facilities to meet the following objectives:

(a) Limit the risk to adjacent facilities.

(b) Provide fire fighting access.

(c) Provide accessibility for operators to perform emergency shutdown actions in the event of a fire,explosion, or other emergency.

(d) Provide evacuation paths for personnel to exit operating units in the event of a fire, vapor release,toxic material spill, or other emergency.

(e) Provide separation of continuous ignition sources from flammable material release sources.

(f) Provide separation to limit the potential of a small fire or vapor release to escalate to a largeremergency with greater losses.

(g) Limit business interruption resulting from fires or explosions.

(h) Provide alternative spacing within the plant by evaluating the consequence of fire, explosion, andtoxic exposure to persons or facilities through the use of the analysis method contained in the Appendix.

3. REFERENCES

The following publications form a part of this Guide. Unless otherwise specified herein, use the latestedition.

Mobil Engineering Guides

EGE 16-B-1 Piping — General DesignEGE 16-B-22 Piping — Process EquipmentEGE 33-B-2 Electrical — Classification of Hazardous Locations in Petroleum Process PlantsEGE 33-B-16 Electrical — Pressurizing Systems for Buildings Housing Electrical FacilitiesEGE 34-B-15 Fireproofing — General RequirementsEGS 101 Site Survey for Design and Construction of Facilities at Grass-Roots LocationsEGS 102 Site Survey — Existing PlantsEGS 301 Design of Plants to Facilitate MaintenanceEGS 323 Blast-Resistant Control BuildingsEGS 581 Incoming Electric Services for Continuous Hydrocarbon Processing FacilitiesEGS 626 Fire Protection — Storage TanksEGS 629 Fire Protection and Loss Prevention — Refineries and Petrochemical PlantsEGS 643 Fire Protection — Fixed Fire Water Spray SystemsEGS 661 Pressure Relief and Vapor Depressuring Systems



NFPA (National Fire Protection Association) Codes

30 Flammable and Combustible Liquids Code43C Storage of Gaseous Oxidizing Materials50 Bulk Oxygen Systems at Consumer Sites496 Purged and Pressurized Enclosures for Electrical Equipment

4. DEFINITIONS

Battery Limits — The boundaries of a process unit establishing outer limits for its equipment.

Central Control House (CCH) — A control house that controls a significant portion of a facility such that itsloss would result in a major shutdown and/or adversely affect the safe shutdown of the facility during anemergency.

Dimensions — Measurements that apply to spacing between equipment, or from equipment to defined lines,and which are "edge-to-edge" dimensions (not "centerline" dimensions).

Fire Fighting Access — A clear path with at least one alternate secondary accessway for fire fighters ormobile equipment, or both, to safely enter or leave a fire area.

Flammable and Combustible Liquids — Flammable liquids are those having flash points below 37.8ºC(100ºF). Combustible liquids are those having flash points at or above 37.8ºC (100ºF). When heated abovetheir flash points, combustible liquids should be treated as flammable liquids. Detailed definitions offlammable and combustible liquids will be found in NFPA 30.

Immediately Dangerous to Life or Health (IDLH) Level — The IDLH level is that maximum concentration fromwhich, in the event of respirator failure, one could escape within 30 minutes without experiencing anyescape-impairing or irreversible health effects. IDLH levels are listed in various documents, including theNIOSH Pocket Guide to Chemical Hazards (available from U.S. Department of Health and Human Services,National Institute for Occupational Safety and Health, Washington, D.C.).

Multi-Unit Control House — A control center that serves several process units. Loss of a multi-unit controlhouse would curtail operation of the facility but would not result in a total shutdown.

Main Pipeway — Pipeways, at grade or elevated on pipe supports, that contain utility lines and product linesfor a number of process units and that are connected to process unit pipeways.

Operator Shelter — A substantial enclosed structure used by multiple operators for activities such as limitedmonitoring, breaks, inclement weather protection, lunch, etc.

Process Equipment — Any components of an operating facility such as vessels, tanks, fired heaters, heatexchangers, rotating equipment, and piping that are part of a process train used in processing material intoa given product or products.

Process Unit — A complete train of equipment in which a material or product is processed and then senteither to the next unit for further processing or to storage. Process units can be separate or can beintegrated with other units. Integrated process units are part of a continuous operation such that they arenot operated independently.

Process Unit Control House — A control center for one process unit (single-unit).



Process Unit Pipeway — Pipeways that are at grade or elevated on pipe supports and contain feed, recycle,and rundown lines, as well as utility lines within a battery limit.

Satellite Instrument Houses (SIH) — Structures that contain instrument and process control equipment forone (single) or more (multi) process units. The structure is separate from the central control house. (AnSIH may also be referred to as a remote instrument enclosure, or RIE, in some locations.)

5. SPACING RECOMMENDATIONS

5.1 Application of the Guide

Governmental regulations or ordinances that contain spacing requirements more stringent than thosecontained in this Guide shall take precedence over the provisions of this Guide.

5.1.1 The provisions of this Guide do not apply to existing plants and facilities that are built to therequirements of previous Mobil Engineering Guides.

5.1.2 Any reductions from the recommended spacing in this Guide shall be subject to each of thefollowing conditions:

(a) The reduction shall be analyzed by using the consequence analysis technique described in theAppendix.

(b) Adequate measures shall be provided to compensate for any increase in risk by providing additionalsafeguards such as fireproofing, automatic water spray systems, emergency shutdown systems, oradditional fire fighting equipment.

(c) Each reduction shall be clearly identified on a drawing along with the proposed additional safeguardsand shall be reviewed with MRDC Loss Prevention or local loss prevention/safety departments, asapplicable.

5.1.3 The separation distances in this Guide are to be measured between the nearest surfaces ofequipment, units, or devices listed or to the nearest edge of a roadway. Spacing required between twopieces of equipment or facilities having different minimum requirements shall be governed by the larger ofthe two requirements.

The separation distances in this Guide are recommended minimum distances unless otherwise noted.Engineering judgment must be used to assure adequate access for fire fighting and maintenance whenapplying the recommendations and when spacing equipment designated as "no minimum" (NM).

5.2 General Requirements

A satisfactory spacing arrangement usually provides direct, unobstructed accessways that are continuousfrom one end of the unit to the other and connected to roads surrounding the unit. The requirementscontained herein shall be considered when using Table 1-A or 1-B or when establishing alternative spacingby using the Appendix. These guidelines should be reviewed when site surveys are conducted for theconstruction of new facilities as specified in EGS 101 and EGS 102.

5.2.1 Terrain

Whenever practical, locate process units, utility, flare, and other areas with similar open flames at a higherelevation than tank farms and other bulk quantities of hydrocarbons in order to minimize the potential forignition of hydrocarbon vapor releases or liquid spills.



Where it is not feasible to locate tank farms at elevations lower than process areas, increased fire protectionmeasures may be required to offset the increased potential for ignition. These measures may include allor some of the following: diversion diking, high-capacity drainage systems, vapor detection placed at releasepoints, and/or increased fire protection systems such as foam, water spray, or similar protection measures.

Similar precautions for spills and vapor releases are needed when siting plants containing extensivequantities of toxic materials.

5.2.2 Prevailing Wind

Prevailing wind should be considered when locating ignition sources such as furnaces and flares. Areaswith high concentrations of personnel, such as office buildings, shop areas, and existing neighboringcommunity areas, should also be considered in reference to prevailing wind to reduce exposure.

5.2.3 Access for Fire Fighting and Maintenance

(a) Access to process units for fire fighting and emergency access shall meet the followingrequirements:

(1) Access from two directions will be provided between integrated layout process units.

(2) Access to a unit for fire control operations shall not depend upon crossing an adjacentoperating unit.

(3) Process units should be provided with fire breaks of at least 6 m (20 ft) approximately every60 m (200 ft) by means of access ways or through equipment layout considerations.

(4) Main accessways should be at least 6 m (20 ft) wide and can act as a fire break. Mainaccessways for fire fighting should not be located under pipeways and should not pass throughadjacent units. They should be provided through process unit areas at 60 m (200 ft) minimumintervals to allow fire fighting from two directions with 30 m (100 ft) hose lengths.

(5) Secondary accessways should be 3.6 m (12 ft) wide for access by fire fighters dragging hoseor 6 m (20 ft) wide with 4.5 m (15 ft) height clearance to permit access by mobile fire fightingequipment.

Secondary accessways may pass under pipeways or through adjacent process units or equipment,provided clearance is adequate. Alternate secondary accessways are necessary to prevententrapment of fire fighters if flammable vapors are present, if a fire flares out of control, or if the windchanges.

(b) The spacing of equipment should also consider access for maintenance. Maintenance requirementsare dependent on the size and type of mechanical equipment to be used. Requirements formaintenance can be found in EGS 301.

Space process units and equipment to permit use of mobile equipment and power tools for servicing andmaintaining equipment during operation and turnaround periods. Overhead clearance under pipewaysand other structural supports is specified in EGE 16-B-1.

5.2.4 Spacing to Public or Noncompany Property

Distances to various equipment and property boundaries can be found in Tables 1-A and 1-B. Careful



consideration should be given to placement of facilities in relation to neighboring community facilities so thatthe risks imposed by potential spills or releases of toxic materials, hydrocarbons, or chemicals can bemaintained.

In general, the spacing to a property boundary that is adjacent to a relatively densely populated area mustbe maintained more stringently than the spacing to a property boundary adjacent to a relatively less denselypopulated area. Examples of densely populated areas are shopping areas, schools, hospitals, public parks,and residential areas. Examples of less densely populated areas are rivers, restricted areas, railroads, andpower company right-of-ways.

5.3 Emergency and Fire Fighting Equipment

5.3.1 Isolation Valves and Pipeways

Main pipeways shall be located outside of process unit battery limits.

Isolation or battery limit valves should be installed in a safe, well-lighted, accessible location at the processunit battery limits. The valves should be accessible from grade or from permanent fixed platforms equippedwith stairway access. There should be access from two directions (such as stairways on both ends ofplatforms) when the isolation valves are in an overhead pipeway. Valves should isolate the unit pipeway andprocess unit from the main pipeway and other process units.

5.3.2 Water Spray Control Valves and Emergency Shutdowns

Shutoff valves for water spray and actuation stations for emergency shutdown shall not be located withinthe same fire areas as the hazard protected by the control equipment. Place water spray valves andshutdown stations so that they are at the battery limits in a well-lighted and easily accessible area. Thewater spray control valve manifold should be located adjacent to the unit control room, where practical, orin a location convenient to the operators. In freezing climates, the strainer, control valve manifold, andnecessary system drains can either be located in a heated area within the control building, in a heatedcubicle, or be insulated and heat traced. For water spray system piping and equipment location andarrangement, see the requirements of EGS 643. See EGE 16-B-22 for specific requirements for emergencyshutdown valves.

5.3.3 Fire Hydrants and Monitors

Fire hydrants protecting process units should be spaced 45 to 60 m (150 to 200 ft) apart around the processunits per EGS 629, Section 9. When possible, locate hydrants so that they are common to two or moreunits. Spacing of monitors in Tables 1-A and 1-B relates only to equipment being protected. Locate firemonitors in accordance with provisions in EGS 629, Section 13.

5.3.4 Fire Stations

Good engineering judgment must be used when evaluating spacing between a fire station and processequipment or other facilities that could potentially release a vapor cloud. Maximum available spacing shouldbe considered in these cases.

5.3.5 Fire Pumps

Spacing requirements can be reduced to 30 m (100 ft) for process equipment and to the toe of the dike ofatmospheric storage tanks when multiple fire pump locations are used and each of the pumps supplies 50



percent or less of the maximum single event required capacity.

5.3.6 Spacing of Emergency Showers and Eyewash Stations

In locations where the eyes or body of any person may be exposed to injurious or corrosive material suchas acids, caustics, or other similar hazardous and toxic materials, an approved safety shower and eyewashfountain are provided for quick drenching and/or flushing of the body and eyes. Locate the safety showerand eyewash fountain for emergency use so that it is as close to the hazardous area as practical withoutcausing a hazard itself, and so that unobstructed access from any point is not more than 15 m (50 ft) awayfrom the hazard. Closer spacing on the order of 3 to 6 m (10 to 20 ft) should be considered for highlycorrosive chemicals and hot oils. In each case, the distance should be evaluated based on informationcontained in the Material Safety Data Bulletin for the hazardous substance.

5.4 Buildings Outside Pro cess Units

Spacing between buildings other than process unit structures, such as shops, laboratories, administration,etc., shall be based on the type of construction and shall conform to the requirements of applicable NFPAcodes, local fire codes, and the specifications of Tables 1-A and 1-B in this Guide, whichever is morestringent.

Spacing recommendations to main pipeways are based on all welded pipe in the pipeway. Sections of thepipeway containing numerous flanges, vents, drains, or other release sources should be treated as processarea pipeways in regard to spacing.

5.5 Process E quipment and Unit Spacing

5.5.1 Process Unit Spacing

Equipment in a process unit should be located 30 m (100 ft) from equipment handling hydrocarbon inadjacent units. This spacing is required to minimize risks due to turnaround maintenance activities in a unitwhile the adjacent unit remains in service. If the process units are integrated, and therefore shut downsimultaneously, the spacing may be reduced to 15 m (50 ft). The minimum distance from a process unitbattery limit to an unrestricted plant roadway should be 15 m (50 ft). Spacing less than 15 m (50 ft) may beconsidered with the addition of proper mitigation and/or control procedures. For example, requiring vehiclepermits on all vehicles that travel on unrestricted plant roadways.

5.5.2 Fired Heaters

Fired heaters are a continuous ignition source and require separation of at least 15 m (50 ft) from processequipment containing flammable liquids. Where hydrocarbons are handled at temperatures aboveautoignition or above 260ºC (500ºF) there is little chance of delayed ignition or vapor cloud formation. Thisallows a reduction in spacing to the minimum required for maintenance and fire fighting. Fired heatersshould be located at process unit battery limits. The prevailing wind direction should be considered whenlocating fired heaters to minimize the potential of igniting vapors.



Locate fired heaters at least 15 m (50 ft) from pumps and compressors and from vents that might releaseignitable vapors. The spacing should be increased to 22.5 m (75 ft) where adjoining vessels will be enteredfor maintenance while a fired heater remains in operation. Process unit pipeways and the heater’s fuel gasknockout pots should be no less than 7.5 m (25 ft) from fired heaters.

5.5.3 Pumps

Pumps should be located in accordance with Tables 1-A and 1B, Figure 1, and as outlined below. Thenormal operating temperatures of the fluids handled by pumps shall be used to determine if the fluid isconsidered combustible, flammable, or above autoignition. Any combustible fluid heated above its flashpoint shall be considered a flammable liquid.

On all process pumps, suction and discharge piping should be arranged to provide easy access to thepumps and associated equipment to eliminate such hazards as tripping or head obstructions.

When locating pumps special consideration should be given to high-pressure and high-temperature pumps.The pumps may be grouped with other pumps that present similar hazards, but should be separated frompumps that present different hazards, to minimize damage due to spill fires. Pumps handling hydrocarbonsabove autoignition or 260ºC (500ºF) may be grouped together but should be located at least 4.5 m (15 ft)from other pumps handling hydrocarbons. Pumps handling flammable liquids at pressures above 3.45 MPagage (500 psig) may be grouped together but should be located at least 4.5 m (15 ft) from other pumpshandling hydrocarbons.

Pump Type Pump Fire Protection Recommended Spacing toPipeways and Air Coolers

Pumps handling combustible With or without water spray systems Adjacent to but not underliquids at temperatures below theirflash points

Pumps handling flammable liquids Without water spray 3 m (10 ft)(or combustible liquids attemperatures above their flash Equipped with water spray systems in Adjacent to but not underpoints) accordance with EGS 643

Pumps handling flammable or Without water spray systems 4.5 m (15 ft)combustible liquids attemperatures above their Equipped with water spray systems in 3 m (10 ft)autoignition temperatures accordance with EGS 643

Pumps handling flammable liquids Without water spray systems 4.5 m (15 ft)(or combustible liquids attemperatures above their flash Equipped with water spray systems in 3 m (10 ft)points) at discharge pressures over accordance with EGS 6433.45 MPa gage (500 psig)

FIGURE 1SPACING OF PUMPS TO FIREPROOFED ELEVATED PROCESS AREA

PIPEWAYS AND STRUCTURALLY SUPPORTED AIR COOLERS



When a pump and its spare are exposed to a common fire hazard, additional separation between them maybe justified. For example, the pumps might have long replacement lead times that could cause excessivebusiness interruption if both were lost in a fire, or the pumps could be exceedingly expensive.

Locate transfer pumps offsite in areas outside of tank dikes. Space the transfer pumps at least 3 m (10 ft)from other nonassociated pumps, at least 15 m (50 ft) from unit substations, a minimum of 60 m (200 ft)from main substations, and 9 m (30 ft) from main pipeways. The increased separation from the mainpipeway is due to the relatively large size of transfer pumps.

The requirements for spacing between pumps and pipeways that have been fireproofed in accordance withEGE 34-B-15 are described in Figure 1. Spacing between pumps handling flammable or combustible liquidsand pipeways that have NOT been fireproofed in accordance with EGE 34-B-15 should be at least 9 m (30ft).

5.5.4 Gas Compressors/Expanders

Gas compressors [over 150 kW (200 hp)] and expanders should be separated from other equipment asspecified in Tables 1-A and 1-B. Steam- or motor-driven gas compressors [less than 150 kW (200 hp)] canbe treated the same as pumps in regard to spacing. All gas compressors should be located at least 15 m(50 ft) away and, if practical, downwind from fired heaters. Do not locate equipment over gas compressors.Suction knockout drums, intercoolers, and intercooler accumulators should be located a sufficient distancefrom the compressor served to provide clear access for fire fighting and maintenance. Generally, spacingof 3.6 m (12 ft) has proven sufficient. Provide access for fire fighting from at least two sides.

5.5.5 Cogeneration Facilities

Gas turbine driven generators using turbine exhaust as combustion air for fired heaters shall be located asclose as practicable to the unit battery limits. Clearances to adjacent equipment shall be equal to or greaterthan those specified for the adjacent heater. Separation between the turbine and fired heater should be atleast 4.5 m (15 ft) and so arranged as to provide access for fire fighting and maintenance. Location of airintake ducts for the turbine combustion air and enclosure ventilation shall be in accordance with Paragraph5.5.11. Location of electrical substations serving the turbine generator and control equipment shall be basedon separation distances specified in Paragraph 5.8 for unit electrical substations or for explosionproofoutdoor switch racks.

Cogeneration plants with the following should be considered utility plant units and should be located andspaced in accordance with Paragraph 5.9:

(a) Gas turbine driven generators with waste heat steam boilers.

(b) Alternative fuel fired boilers such as a fluid bed boiler burning petroleum coke.

(c) Auxiliary fuel gas and boiler feedwater treating equipment.

Spacing requirements should be determined by considering the turbine generator unit and attached wasteheat boiler as one unit. The unit should be located in accordance with separation distances applicable toa boiler in Tables 1-A and 1-B. Air intakes for gas turbine combustion air and enclosure ventilation shall belocated in accordance with Paragraph 5.5.11. Substations associated with a cogeneration plant may be partof a main substation, an outdoor switch rack, and possibly connected with a public utility system. A loss ofthe substation will have a major effect on refinery operations. Locate the substation as specified inParagraph 5.8.



5.5.6 Heat Exchangers

The access required for heat exchanger maintenance usually is sufficient for safety and fire fighting. Dangerto personnel should be considered if the heat exchangers are opened and cleaned during process unitoperation. For maintenance access, spacing should be sufficient to permit safe blinding and for tube bundleremoval without damage to, or removal of, adjacent piping or valves. Equipment should not be locatedabove heat exchangers containing flammable or combustible liquids over 260ºC (500ºF).

5.5.7 Air Coolers Containing Hydrocarbons

Vessels and/or pumps containing flammable or combustible liquids should not be located beneath aircoolers. Air coolers should be spaced 15 m (50 ft) from positive ignition sources such as fired heaters. Heatexchangers containing hydrocarbons over 260ºC (500ºF) should not be located beneath air coolers.

When the air cooler is located over a process unit pipe rack, the clearance between the lowest portion ofan air cooler and the uppermost pipe should be 2.4 m (8 ft) minimum. Flanges and valves in hydrocarbonpipelines should be minimized beneath an air cooler. Multiple flanges and valves such as in control stationsshould not be located under air coolers. Equipment shall not be located above air coolers.

See Paragraph 5.5.3 for spacing between air coolers and pumps.

5.5.8 Desalters

Desalters contain large quantities of flammable crude oil. Preferably, they should be located on the unitperiphery. A low diked enclosure should be provided, sized for 10 percent of the desalter contents and witha fire sealed drain to safely convey spills to the oily water sewer. The potential effects of a spill fire from thedesalter should be considered when locating equipment adjacent to the desalter area.

5.5.9 Towers and Vessels

Towers and vessels should be spaced at least 3 m (10 ft) from unit pipeways. Reduced spacing is permittedwhen adequate access for fire fighting and maintenance can be maintained. Towers and vessels shouldbe located at least 15 m (50 ft) from fired heaters or fired reboilers. Equipment integrated with major towerssuch as unfired reboilers, overhead exchangers, and feed effluent exchangers may be located closer to thefractionating column that they are associated with than is indicated in the Tables. However, access for firefighting and maintenance must be maintained. Vessels containing flammable or combustible liquids shouldnot be located beneath pipeways or air coolers.

5.5.10 Onsite Tanks

Atmospheric storage tanks within process unit battery limits should be limited to a maximum size of 80 m3

(500 bbl) capacity when they contain flammable liquid or a combustible liquid heated above its flash point.Storage tanks should be spaced so that at least 9 m (30 ft) separation is provided between enclosure dikesand process unit equipment. Atmospheric storage tanks containing combustible liquids below their flashpoint should be considered as process vessels in regards to spacing with the spacing being measured tothe dike. Process equipment and pumps should not be located in diked areas. Diked enclosures meetingprovisions of NFPA 30 shall be provided for all storage tanks placed in process units. Diked areas will besized for the largest tank in the diked area and shall be provided with fire sealed drains piped to the oilywater sewer or chemical drain system. Drains shall be equipped with a shutoff valve, located outside of thediked area. The shutoff valve should be the indicating type that readily shows valve position.

5.5.11 Air Intakes



A fresh air intake from a safe location is required for buildings and equipment containing electrical equipmentor other ignition sources when these are located in areas containing flammable vapors. Failure to provideair that is free of flammable vapors will present the possibility of igniting vapors, resulting in an explosion.Equipment and buildings that require protected air supplies include the following:

(a) Internal combustion engines and turbines.

(b) Air compressors.

(c) Inert gas generators.

(d) Forced draft furnaces.

(e) Electrical equipment boxes.

(f) Buildings that contain unclassified electrical equipment.

(g) Boilers.

The location of air intakes in relation to adjacent equipment must be carefully selected by taking into accountprevailing wind direction, probable horizontal and vertical vapor dispersion patterns, and the hazard thatresults from possible formation of a flammable vapor/air mixture. Locate air intakes a minimum of 7.5 m (25ft) abovegrade when within 15 m (50 ft) of process units or within 30 m (100 ft) of process units containingvolatile hydrocarbons. When air intakes serve large internal combustion sources, such as gas turbines,special care should be taken in siting the intake to avoid significant reduction in turbine efficiency.Calculation of air intake design should include an analysis of the effect of the intake on surrounding airpatterns to ensure that air flow to the intake is above the 7.5 m (25 ft) minimum level. Air intakes shouldbe located, to the extent practicable, outside any hazardous electrically classified area in accordance withEGE 33-B-2. Air intakes for pressurized electrical control and equipment areas shall be arranged inaccordance with EGE 33-B-16, Paragraph 3.3.1.

Where air conditioning equipment is utilized for buildings within 150 m (500 ft) of hydrocarbon processingplants, features such as gas detection and shutdown, in addition to the location of the air intake, should beconsidered in order to protect personnel in the building from toxic or nuisance vapors.

5.5.12 High Skin Temperature Equipment

Diesel engines, gasoline engines, and combustion gas turbines present a constant source of ignition forpossible hydrocarbon releases and should be carefully located. Such equipment should be insulated andotherwise isolated by passive systems to maintain a low outer surface temperature. Provide a minimumseparation of 10.5 m (35 ft) between high skin temperature equipment and equipment handling hydrocarbonsbelow autoignition temperature or below 260ºC (500ºF).

5.5.13 Equipment Handling Nonflammables, Noncombustibles, or Nontoxics

As reflected in Tables 1-A and 1-B, there is no established recommended minimum spacing from mostequipment to equipment handling nonflammables, noncombustibles, or nontoxics. When locating this typeof equipment considerations must be given to the following:

(a) Criticality of the equipment (i.e., equipment necessary to control or mitigate emergencies or safelyshut down process equipment should be located as other emergency equipment).



(b) Relative expense, replacement time, and importance to the operation of the facility (i.e., if critical,the equipment should be located away from high fire potential equipment).

The electrical classification of the equipment must be considered relative to the surrounding equipment andthe area classification.

5.6 Control Hou ses and Operator Shelters

Spacing for control houses is as shown in Tables 2-A and 2-B and as outlined below. For electricalclassification, see EGE 33-B-2. Central, multi-unit, and process unit control houses shall be pressurizedin accordance with EGE 33-B-16.

Control houses should be a minimum of 30 m (100 ft) from the property boundary unless local policy dictatesotherwise. Spacing of up to 60 m (200 ft) from central control houses to the property boundary may besubject to local security regulations.

5.6.1 Central Control Houses

Central control houses should not normally be a part of administration buildings, laboratories, or any othernonrelated structure. If it is necessary to combine a nonblast resistant central control house with anonrelated structure, the control house must be separated by a 3-hour rated fire wall without any directaccess or penetration of the fire wall. The central control house may share switchgear housing with asubstation if isolated from the switchgear by a 3-hour rated fire wall and if precautions are taken to limitpotential fire exposure associated with the transformers (sloping the ground away from the control house,fire walls between control house and transformers, etc.).

Central control houses should be located adjacent to a plant roadway to ensure access during anemergency. One side of the central control house should have an open buffer zone of at least 75 m (250ft) from process equipment. To reduce hazard in the event of a large vapor or toxic discharge during anemergency, process units handling toxic materials or flammable liquids or gases at pressures over 3.45 MPagage (500 psig) should be located as far as practical from the central control house.

Central control houses should be located at least 150 m (500 ft) from LPG loading racks or processequipment containing flammable or combustible liquids and/or vapors that could form a vapor cloud uponrelease (unless blast-resistant construction per EGS 323 is utilized) and at least 60 m (200 ft) from all otherprocess equipment containing hydrocarbons. The 60 m (200 ft) spacing requirement is provided for fireexposure considerations.

Central control houses, which are built to the blast-resistant construction criteria of EGS 323, should belocated at least 60 m (200 ft) from process equipment containing hydrocarbons.

Central control houses should be located no closer than 60 m (200 ft) to tanks containing nonheatedcombustible material. Flammable materials, toxic materials, and crude or heavy oils that are prone toboilover in fire situations should be stored a minimum of 150 m (500 ft) from the central control house.

Central control houses should be located no closer than 30 m (100 ft) to process area pipeways and mainpipeways. The pipeways should contain straight run piping with no valves or flanges within 60 m (200 ft)of the control house. Sections of the pipeway that contain groupings of release sources (such as flanges,vents, drains, instrument connections, etc.) and also contain products that could form a vapor cloud uponrelease should be located at least 150 m (500 ft) from nonblast resistant central control houses.



5.6.2 Multi-Unit Control Houses

Multi-unit control houses should not normally be a part of administration buildings, laboratories, lunchrooms,or any other nonrelated structure. If it is necessary to combine a nonblast resistant multi-unit control housewith a nonrelated structure, the control house must be separated by a 3-hour rated fire wall without anydirect access or penetration of the fire wall. The multi-unit house may share switchgear housing with asubstation if isolated from the switchgear by a 3-hour rated fire wall and if precautions are taken to limitpotential fire exposure associated with the transformers (sloping the ground away from the control house,fire walls between control house and transformers, etc.).

One side of the multi-unit control house should have an open buffer zone of at least 75 m (250 ft) fromprocess equipment. To reduce hazard in the event of a large vapor or toxic discharge during an emergency,process units handling toxic materials or flammable liquids or gases at pressures over 3.45 MPa gage (500psig) should be located as far as practical from a multi-unit control house.

Multi-unit control houses should be located at least 150 m (500 ft) from LPG loading racks or processequipment containing flammable or combustible liquids and/or vapors that would potentially form a vaporcloud upon release (unless blast-resistant construction per EGS 323 is utilized) and at least 30 m (100 ft)from all other process equipment containing hydrocarbons.

Multi-unit control houses that are built to the blast-resistant construction criteria of EGS 323 should belocated at least 30 m (100 ft) from process equipment containing hydrocarbons. The 30 m (100 ft) spacingrequirement is provided for fire exposure considerations.

Multi-unit control houses should be located no closer than 30 m (100 ft) to process area pipeways and nocloser than 9 m (30 ft) to main pipeways if the main pipeways are of welded construction and have noconcentrations of flanges or other potential release sources within 30 m (100 ft) of the control house.

5.6.3 Process Unit Control Houses

Process unit control houses should be located at least 60 m (200 ft) from nonassociated process equipment(not a part of the unit being served) that contains flammable or combustible liquids and/or vapors that wouldpotentially form a vapor cloud upon release. Spacing less than 60 m (200 ft) is acceptable if theblast-resistant construction criteria for control rooms per EGS 323 is utilized. The 60 m (200 ft) spacing isrequired in order to protect against a blast in an adjacent unit that could destroy the control house andadversely affect a safe shutdown of the unit served by it. The 60 m (200 ft) spacing requirement alsoprovides greater reliability of the unit in regard to operation after a blast in an adjacent unit.

Process unit control houses should be located at the periphery of the process unit, should not be clusteredin the same general area, and should be at least 15 m (50 ft) from any process equipment containingflammable liquids or vapors. The 15 m (50 ft) spacing requirement to all equipment handling hydrocarbonsis provided for fire exposure considerations.

5.6.4 Operator Shelters

Operator shelters should be located at least 15 m (50 ft) from the nearest process unit equipment containingflammable liquids or vapors, and 15 m (50 ft) from fired heaters.

5.7 Satellite Instrument Houses (SIHs)



Spacing for satellite instrument houses (SIHs) is shown in Tables 2-A and 2-B and outlined below.

Satellite instrument houses should be located a minimum of 30 m (100 ft) from the property boundary unlesslocal policy dictates otherwise. Locate satellite instrument houses at the unit battery limits so that accessto the structure can be gained without traversing a process unit. Consideration should be given in locatingthe structure to minimizing exposure from heaters and fired equipment, vessels containing a large inventoryof toxic or flammable liquids, vents, or flares. Exposures to large rotating equipment containinghydrocarbons, such as compressors, expanders, and pumps operating above 260ºC (500ºF) or in excessof 3.45 MPa gage (500 psig), should also be minimized.

Provisions in Paragraph 5.5.11 shall apply to location of purging air intakes if SIHs are pressurized tomaintain appropriate area classification as per EGE 33-B-16 and NFPA 496. All SIHs should be providedwith fire, heat, or smoke detection. Fire protection (portable or fixed) shall be provided in multi-unit SIHs toextinguish and control fires caused by malfunction/short circuit of the electrical and electronic equipment.

5.7.1 Single-Unit Satellite Instrument Houses (SIHs)

In addition to the requirements above, satellite instrument houses serving a single process unit should belocated at least 60 m (200 ft) from nonassociated process equipment (not a part of the unit being served)that contain flammable or combustible liquids and/or vapors that would potentially form a vapor cloud uponrelease. Spacing of less than 60 m (200 ft) is acceptable if the blast-resistant construction criteria for controlrooms per EGS 323 is utilized. The 60 m (200 ft) spacing is required in order to protect the SIH from a blastin an adjacent unit that could destroy the SIH and adversely affect a safe shutdown of the unit served by theSIH. The 60 m (200 ft) spacing requirement also provides greater reliability of the unit in regard to operationafter a blast in an adjacent unit.

Single-unit SIHs should not be clustered in the same general location and should be located at least 15 m(50 ft) from any process equipment containing flammable liquids or vapors. The 15 m (50 ft) spacing fromequipment containing hydrocarbons is provided for fire exposure considerations.

5.7.2 Multi-Unit Satellite Instrument Houses (SIHs)

In addition to the requirements above, satellite instrument houses serving more than one unit should belocated at least 150 m (500 ft) from any process equipment containing flammable or combustible liquidsand/or vapors that would potentially form a vapor cloud upon release. As in single-unit instrument houses,spacing less than 150 m (500 ft) is acceptable if the blast-resistant construction criteria for control roomsper EGS 323 is utilized. The 150 m (500 ft) spacing is required in order to protect the SIH from a blast thatcould destroy the SIH and adversely affect the safe shutdown of the units served by the SIH. The 150 m(500 ft) spacing requirement also provides greater reliability of the units served by the SIH in regard tooperation after a blast.

Multi-unit SIHs should not be part of administration buildings, laboratories, or any other nonrelated structure.Where it is deemed absolutely necessary to combine a multi-unit SIH and a nonrelated structure, the SIHmust be separated from the structure by a 3-hour rated fire wall without direct access or any otherpenetrations through the fire wall.

Multi-unit satellite instrument houses should be located at least 30 m (100 ft) from any process equipmentcontaining flammable liquids or vapors that would not form a vapor cloud upon release. The 30 m (100 ft)spacing requirement to all equipment handling hydrocarbons is provided for fire exposure considerations.

5.8 Electrical Substations



Spacing for substations is shown in Tables 2-A and 2-B and outlined below.

Substations should be located a minimum of 30 m (100 ft) from the property boundary unless local policydictates otherwise.

Main and multi-unit substations should not be part of administration buildings, shops, control buildings,laboratories, or any other nonrelated structure. In locations where it is deemed absolutely necessary tocombine a main or multi-unit substation with another structure, the substation must be separated by a 3-hourrated fire wall with no direct access or any other penetration through the wall.

5.8.1 Main Substations

Main substations typically house the electrical distribution systems for all incoming power sources to a plant.The substation must be protected in the event of a plant fire, explosion, or other emergency in order toprovide power to support plant emergency systems. Loss of a main substation can cause extensivebusiness interruption as the equipment in the substation is generally long lead time items.

The main substation for the entire refinery or petrochemical plant should be 150 m (500 ft) minimum fromprocess equipment containing flammable or combustible liquids and/or vapors that would potentially forma vapor cloud upon release; see also EGS 581 for additional considerations. Spacing less than 150 m (500ft), as well as blast-resistant construction, may be considered with Mobil approval after studying the severityand impact of potential blast damage to enclosed and nonenclosed equipment within the substation. Thepreferred location for a main substation is as close to the property line as security permits.

Main substations should be located no closer than 30 m (100 ft) to main pipeways and 30 m (100 ft) toprocess area pipeways. Sections of the pipeway that contain groupings of release sources (such as flanges,instrument connections, etc.) and products that could form a vapor cloud upon release should be locatedat least 150 m (500 ft) from main substations.

5.8.2 Process Unit Substations

The spacing requirements for single-unit and multi-unit substations are as shown in Tables 2-A and 2-B andas outlined below. The spacing requirement for blast-resistant construction provides greater reliability ofthe unit served by the substation in regard to operation of the unit after a blast in an adjacent unit. The 15m (50 ft) spacing requirement to all equipment handling hydrocarbons is provided for fire exposureconsiderations.

(a) Single-Unit Substations

Single-unit substations enclosed in buildings or within weatherproof enclosures should be located atleast 15 m (50 ft) from process equipment handling hydrocarbons. Single-unit substations should alsobe located at least 60 m (200 ft) from nonassociated process equipment (not a part of or integrated withthe unit being served) that contains flammable or combustible liquids and/or vapors that would potentiallyform a vapor cloud upon release. Spacing of less than 60 m (200 ft) is acceptable if the blast-resistantconstruction criteria for control rooms per EGS 323 are utilized.

(b) Multi-Unit Substations Serving Integrated Units

Multi-unit substations serving only units that are integrated should be located at least 15 m (50 ft) fromprocess equipment handling hydrocarbons. They shall also be located at least 60 m (200 ft) from



process equipment containing flammable or combustible liquids and/or vapors that would potentially forma vapor cloud upon release and which are in units not integrated with the units being served by thesubstation.

(c) Multi-Unit Substations Serving Nonintegrated Units

Multi-unit substations serving units that are not integrated should be located at least 15 m (50 ft) fromprocess equipment handling hydrocarbons. They should also be located at least 75 m (250 ft) from anyprocess equipment containing flammable or combustible liquids and/or vapors that would potentially forma vapor cloud upon release. As in single-unit substations, spacing less than 75 m (250 ft) is acceptableif the blast-resistant construction criteria for control rooms per EGS 323 is utilized.

5.8.3 Explosionproof Outdoor Electrical Switch Racks

Spacing between critical electrical switch racks (switch racks associated with shutdown or emergencyactions on process equipment) and equipment handling hydrocarbons should be 6 m (20 ft) minimum,except that 15 m (50 ft) of spacing should be provided away from fired heaters and gas compressors.Noncritical switch racks should meet electrical classification criteria for spacing.

5.9 Utility Facilities

Boilers and utility equipment should be spaced to prevent exposure to fire or explosion damage. Loss ofsteam may result in a complete plant shutdown with increased risk due to the possibility of fire and explosionin process units. Within the utility plant area, control rooms, feedwater pumps, deaerators, and so forth maybe spaced in accordance with good engineering judgment to provide adequate spacing for operation andmaintenance. Fuel oil day tanks, fuel oil pumps, and heat exchangers should be spaced 9 m (30 ft) awayfrom other utility equipment. Fired steam generators and ancillary equipment should be located 30 m (100ft) minimum from process equipment handling flammable and combustible liquids and gases. Waste heatsteam generators that have supplemental firing and are part of a process unit should be spaced inaccordance with requirements for fired heaters (see Paragraph 5.5.2).

5.9.1 Plant Air and Instrument Air Compressors

When plant air and instrument air compressors are located in a central utilities plant, they may be locatedadjacent to the boiler area. Instrument air compressors in vital service should be separated by distancesas shown in Tables 1-A and 1-B for fired steam boilers and power generators. Instrument air compressorsmay be located adjacent to control houses provided a safe source of air is furnished in accordance withParagraph 5.5.11.

5.9.2 Cooling Towers

Cooling towers should be spaced at least 30 m (100 ft) from process equipment. Where possible, coolingtowers should be downwind from substations, pipeways, and process equipment so that fog developed willnot cause corrosion or obstruct vision. Cooling towers have been known to be a source of hydrocarbonrelease.

5.10 Offsite Tank Storage

5.10.1 Atmospheric Storage Tanks

Spacing between process unit equipment and offsite storage tanks shall be a minimum of 60 m (200 ft).For tanks exceeding 45 m (150 ft) in diameter, radiation calculations based on provisions in the Appendix,will be made for fire involvement of the full dike area to confirm that heat exposure from a dike area fire will



not adversely affect the process equipment in the process units. Process unit grade level should be at least0.6 m (2 ft) above adjacent tank area grade level. Locate low-pressure storage tanks downgrade anddownwind of ignition sources in process units.

The spacing from offsite storage tanks to substations, satellite instrument houses, and control housesshould be as follows:

(a) For satellite instrument houses, control houses, and for process unit substations:

(1) A minimum of 60 m (200 ft) from the tank shell and 30 m (100 ft) from the top of the dike fortanks greater than 80,000 bbl capacity and less than 45 m (150 ft) in diameter.

(2) A minimum of 30 m (100 ft) from the tank shell and 15 m (50 ft) from the top of the dike fortanks less than 80,000 bbl capacity and less than 45 m (150 ft) in diameter.

(3) Crude storage should be spaced as far as practical from substations, satellite instrumenthouses, and control houses.

(4) For tanks over 45 m (150 ft) in diameter, see the Appendix.

(5) For central control houses see Paragraph 5.6.1.

(b) For substations serving offsite storage areas only:

(1) A minimum of 30 m (100 ft) from the tank shell and 15 m (50 ft) from the top of the dike.Transformers may be located between the top edge of the dike and the substation.

(2) For tanks over 45 m (150 ft) in diameter, see the Appendix.

(3) Crude storage should be spaced as far as practical from substations, satellite instrumenthouses, and control houses.

(4) Consideration should be given to the potential consequences of exposing substations, satelliteinstrument houses, and control houses to tank fires. The need to pump products during a fire, thepotential loss of emergency shutdown, and potential business interruption should be considered.

Storage tanks in high-flash lube oil service with flash points of 93ºC (200ºF) or higher and stored at ambienttemperature should be spaced 30 m (100 ft) or more from process units, other refinery equipment, andrefinery boundary limits.

Space between tanks and arrangement of atmospheric storage tanks shall be in accordance with EGS 626,Section 5. Low-pressure storage tanks operating at pressures of 3.4 kPa gage (0.5 psig) but not to exceed103.4 kPa gage (15 psig) shall be spaced and arranged in accordance with provisions of EGS 626, Section7, and NFPA 30.

5.10.2 High-Pressure Storage Tanks

High-pressure storage tanks, in excess of 103.4 kPa gage (15 psig), shall also be located and arranged inaccordance with provisions of EGS 626, Section 8.

Spheres and cylindrical pressure storage vessels should be spaced a minimum of 60 m (200 ft) fromprocess unit equipment. However, a minimum of 75 m (250 ft) should be maintained from a continuoussource of ignition, such as a heater. Locate these tanks downgrade and downwind from ignition sources.



Horizontal cylindrical vessels should not be oriented so that their longitudinal axis is pointed toward offices,shops, or process units that are located closer than 450 m (1500 ft) to the vessels. Onsite pressure storagerequired for processing, such as solvent propane, should have the same spacing as specified foraccumulators.

5.10.3 Refrigerated and Cryogenic Liquid Storage Tanks

The location, arrangement, and spacing of refrigerated and cryogenic storage tanks shall be in accordancewith provisions of Section 7 of EGS 626. The tanks should be a minimum of 75 m (250 ft) from processequipment. Refrigerated and cryogenic storage tanks should be located downgrade and downwind fromignition sources in process units.

5.11 Loading and Unloading Facilities

5.11.1 Truck Loading Racks

Truck loading racks for flammable and combustible liquids should be located near the plant gates to avoidtruck traffic near process areas. They should be spaced from other plant facilities as specified in Tables 1-Aand 1-B.

LP-gas truck loading racks should be spaced 75 m (250 ft) from process equipment, at least 45 m (150 ft)from other types of truck loading racks, 60 m (200 ft) from atmospheric or pressure storage tanks, and 150m (500 ft) from administration buildings.

5.11.2 Tank Car Loading Racks

Tank car loading racks for flammable and combustible liquids should be located to avoid road blockagewhen spotting rail cars, ensuring passage for fire trucks or other service vehicles at all times. Loading rackshandling low-flash material should be spaced at least 60 m (200 ft) from process equipment handlinghydrocarbons. Racks should be located so that locomotives do not traverse within 15 m (50 ft) of processunit battery limits or tank storage. LP-gas tank car loading racks should be spaced 75 m (250 ft) fromprocess equipment and all tank storage and at least 30 m (100 ft) from other types of tank car loading racks.

5.11.3 Petroleum Piers and Wharves

Wharves handling flammable liquids should be spaced a minimum of 60 m (200 ft) from process unitequipment handling hydrocarbons. Wharves should be spaced at least 75 m (250 ft) from fired heaters orother continuously exposed sources of ignition. Wharves handling LP-gas should be spaced at least 75 m(250 ft) from other refinery facilities and from wharves handling flammable liquids.

5.12 Flares

Spacing of elevated flares from process equipment depends on the flare stack height, flare load, and theallowable heat intensity at the equipment location as calculated in EGS 661. Flare stack locations shouldbe curbed to contain hydrocarbon carryover and should be at least 60 m (200 ft) from process equipmentcontaining hydrocarbons, except for flare knockout drums. See EGS 626 for spacing requirements forstorage tanks.

The elevation change between the flare and the process area should be considered when locating the flare.In general, the flare should be located to minimize the potential for ignition of vapor released from theprocess units.



Radiant heat intensity during potential emergencies should be calculated for areas where personnel maybe present and/or where the public has free access. To calculate spacing requirements of elevated flares,refer to EGS 661. Where burn pits or flares at grade are provided, a minimum spacing of 150 m (500 ft)should be provided to equipment containing hydrocarbons or to the plant boundary.

5.13 Other Offsite Fac ilities

5.13.1 Wastewater Separators

Wastewater separators handling hydrocarbons should be spaced at least 30 m (100 ft) from process unitequipment handling flammable liquids and 60 m (200 ft) from heaters or other continuous sources of ignition.Preferably, wastewater separators should be located downgrade of process equipment and tankage.

5.13.2 TML and TEL Blending Plants

Tetramethyl lead (TML) and tetraethyl lead (TEL) blending plants should be spaced 30 m (100 ft) fromprocess equipment handling flammable liquids and 45 m (150 ft) from fired heaters or other continuouslyexposed sources of ignition. Arrange to prevent draining of any flammable liquids near TML and TEL plants.TEL/TML storage and blending plants should be located as far as is practical from administration, shop,control, major plant roadways, and other onsite population centers to minimize the effects on personnel inthe case of a spill or leak.

5.13.3 Blowdown Drums

Blowdown drums are used for liquid relief of flammable and toxic fluids in emergencies and are not usuallyinstalled when a suitable pressure-relieving system and flare are provided. When used, blowdown drumsshould be 30 m (100 ft) minimum from process unit battery limits and 60 m (200 ft) from storage tanks andother refinery facilities.

5.13.4 Fire Training Areas

Fire training areas are ignition sources when in use. Because of the smoke produced, they can also createa nuisance for the refinery and neighboring facilities. Fire training areas should be 60 m (200 ft) fromprocess unit battery limits, main control rooms, fired steam generators, fire pumps, cooling towers, and alltypes of storage tanks. They should also be at least 75 m (250 ft) from property boundaries; administration,shop, and similar buildings; and from the main substation.

5.13.5 Compressed and Liquefied Gas Storage

(a) Portable Gas Cylinders

Supplies of various industrial gases, when located in process units, should be placed where vulnerabilityto fire exposure is at a minimum. Installations involving multiple cylinders of flammable or toxic liquidsshould be located as close as practicable to the unit battery limit, at least 7.5 m (25 ft) from hydrocarbonequipment, and as near to the plant gate as practicable to avoid truck traffic near process areas. Firefighting access shall be provided. Bulk storage of cylinders shall be located in a remote offsite area, aminimum of 60 m (200 ft) from process units.



(b) Refrigerated Containers of Industrial Gases

Bulk liquefied oxygen, chlorine, and nitrogen each present significant problems to overall plant safety.Reactive and oxidizing gases such as oxygen and chlorine in refrigerated containers shall not be locatedwithin process plant battery limits. Locate storage containers on periphery of the entire process area.Remote location minimizes the significant hazard of having tank trucks of refrigerated reactive andoxidizing liquid gases entering hydrocarbon process unit locations. Arrangement of bulk oxygen suppliesshall be in accordance with NFPA 50 and bulk chlorine supplies in accordance with NFPA 43C. Liquidnitrogen containers should be located in areas relatively free of exposure to fire and mechanical damagein accordance with vendor recommendations.

5.13.6 Railroad Tracks

Process equipment, except flares, should be located at least 60 m (200 ft) from railroad main lines; flaresshall be located as specified in EGS 661. Spacing to tankage should be as specified in EGS 626 and NFPA30. Spur tracks for refinery use should be outside process unit battery limits and 15 m (50 ft) from processequipment, except for coke handling purposes.

6. PROCESS EQUIPMENT SPACING TABLES

Tables 1 and 2 have been developed to indicate the recommended minimum spacing for process units fromother refinery facilities, from adjacent process units, and the minimum recommended spacing betweenequipment within process units. SI (metric) units are given in Tables 1-A and 2-A; customary units are givenin Tables 1-B and 2B.



APPENDIX

EVALUATION PROCEDURE FOR DETERMINING ALTERNATIVE SPACING REQUIREMENTS

From time to time, it may be necessary to evaluate alternative spacingrequirements between process units and adjacent equipment, hazards, andfacilities. This action may be taken where site limitations reduce the spaceavailable for process unit separation from adjacent units or where neighboringplants and communities must be considered. In either case, the procedure thatfollows offers guidelines for the evaluation of alternatives proposed to reducespacing or for examination of required spacing:

(1) Identify the hazards inherent in the process unit, plant, or exposingfacility.

(2) Estimate the consequences that could result from accidents involvingthe hazards identified.

(3) Identify the opportunities to reduce the consequences.

(4) Calculate the heat radiation, blast pressure, and/or fire effects onexposed process or offsite equipment or facilities or areas adjacent to Mobilproperty. For toxic hazards, calculate the extent of a possible toxic clouddispersion. When these calculations are performed, it should be assumedthat any measures taken to reduce the consequences of accidents areeffective.

(5) Identify measures to reduce the impact of the calculated effects andrecalculate the consequences assuming implementation of these measures.

(6) Based on the results of Item (5), review spacing based on Tables 1-Aand 1-B and determine new separation distance. In general, the radiationlevels in the target area shall not exceed 4.73 kW/m (1500 Btu/h/ft ) for2 2

personnel exposure, and 18 kW/m (5700 Btu/h/ft ) for process equipment2 2

exposure. Blast wave pressure shall not exceed 3.4 kPa (0.5 psi) andNIOSH-recommended and IDLH levels shall not be exceeded at the propertyboundary.

(7) All scenarios, calculation methods, and formulas, will be presented toMobil for review prior to conducting the analysis. Once preliminary results areobtained, the recommendations for spacing and the results of the studies willbe presented for review and approval.

Documents

Mobil Egs 303 (1993) Recommended Spacing Within Operating Facilities