Fire Protection in Refineries API RECOMMENDED PRACTICE 2001 NINTH EDITION, APRIL 2012 Fire Protection in Refineries Downstream Segment API RECOMMENDED PRACTICE 2001 NINTH EDITION, APRIL 2012 Special N[.]
Purpose
This recommended practice aims to enhance the understanding of fire protection in refineries, outlining essential steps for the safe storage, handling, and processing of petroleum and its products A key principle of this standard is that effective fire prevention serves as the cornerstone of comprehensive fire protection.
Scope
This document outlines essential principles of fire prevention and protection in refineries, focusing on the chemistry and physics of refinery fires It highlights the influence of refinery system design and infrastructure on fire risk and consequences Additionally, it details common fire control and extinguishing systems used in refineries, emphasizes fire protection strategies relevant to operating and maintenance practices, and offers insights into the organization and training of refinery emergency responders Many discussed concepts, systems, and equipment are elaborated upon in referenced publications, standards, or governmental regulations.
Concept of Hazard vs Risk
Hazards refer to conditions or characteristics of materials that can lead to harm Key hazards in industrial settings include flammability, toxicity, corrosivity, and the presence of stored electrical, chemical, or mechanical energy.
Risk involves exposure to hazards For instance, contact with a hot surface can lead to thermal burns, while corrosive acids can result in chemical burns Such injuries only occur when there is direct contact with the skin.
Working at elevated heights involves "stored energy," which poses a risk of injury in the event of a fall However, this risk only exists when individuals are actually working at heights and exposed to the hazard Without the potential for exposure, there is no associated risk.
Assessing risk levels for any activity requires identifying hazards and estimating the likelihood and severity of exposure events that may cause harm or damage The principles that connect hazards to risk are applicable for evaluating risks to property and the environment For example, hydrocarbon vapors mixed with air can ignite when exposed to an ignition source, potentially leading to fires that cause property damage and personal injury While hydrocarbons are classified as hazardous materials, the risk also involves the presence of a flammable fuel-air mixture in proximity to an ignition source.
The referenced documents are essential for applying this document within U.S federal OSHA jurisdiction Only the cited edition applies for dated references, while the latest edition, including amendments, is relevant for undated references The bibliography categorizes other references and additional information by primary subject area, with further details accessible through the cited Internet sites.
NFPA 30 1 , Flammable and Combustible Liquids Code
1 National Fire Protection Association, 1 Batterymarch Park, Quincy, Massachusetts 02169, www.nfpa.org.
OSHA 29 CFR 1910.38 2 , Emergency Action Plans
OSHA 29 CFR 1910.119, Process Safety Management of Highly Hazardous Chemicals
OSHA 29 CFR 1910.120, Hazardous Waste Operations and Emergency Response
OSHA 29 CFR 1910.132, Personal Protective Equipment
OSHA 29 CFR 1910.156, Subpart L—Fire Brigades
For the purposes of this document, the following definitions apply Additional definitions and an expanded discussion of fire-related hydrocarbon properties and phenomena are included in Section 4 and Annex A.
Electrically nonconducting volatile or gaseous fire suppression agents, approved by the U.S Environmental Protection Agency (EPA), serve as eco-friendly alternatives to ozone-depleting chemicals being phased out under the Clean Air Act (CAA) These clean agents evaporate without leaving any residue.
According to the NFPA, a combustible material is any solid that is capable of burning or any liquid with a flash point of 100 °F (37.8 °C) or higher For more detailed classifications of combustible liquids, refer to NFPA 30.
The rapid reaction of oxidizable material with an oxidizer, usually oxygen from the air, followed by the development of heat This reaction usually produces flames.
A fine powder composed of tiny particles, typically sodium bicarbonate, potassium bicarbonate, or ammonium phosphate, is specially treated to enhance flow properties and is designed for use against Class A (combustible), Class B (flammable), and Class C (electrical) fires, as detailed in NFPA 17.
A study used to evaluate fire hazards in a specific potential fire area and evaluate consequences of fire-related events
According to the NFPA, a flammable substance is any gas that can ignite or any liquid with a flash point below 100 °F (37.8 °C) The outdated term "inflammable" is no longer in use For more detailed classifications of flammable liquids, refer to NFPA 30.
2 U.S Department of Labor, Occupational Safety and Health Administration, 200 Constitution Avenue, NW, Washington, DC
For effective fire protection, an aggregate of air-filled bubbles is utilized, which floats on the surface of flammable liquids These bubbles are created from aerated solutions of water mixed with an appropriate proportion of foam concentrate, potentially including a film-forming agent.
Material capable of undergoing combustion It is the material that burns to feed a fire.
A furnace or heater running in a fuel-rich condition.
A situation or inherent chemical or physical property with the potential to do harm (flammability, oxygen deficiency, toxicity, corrosivity, and stored electrical, chemical, or mechanical energy).
The process of Management of Change (MOC) involves identifying, evaluating, and addressing needs related to changes in process technology, equipment, materials, or procedures beyond simple replacements Additionally, some facilities implement MOC principles to enhance personnel and organizational effectiveness.
The refinery equipment, vessels, and piping in which refining takes place to “process” crude oil to manufacture petroleum products
The property of a material to self-heat and ignite in the presence of atmospheric oxygen.
The probability and consequences of exposure to a hazard, hazardous environment or situation that could result in harm
The identification and analysis, either qualitative or quantitative, of the likelihood and outcome of specific hazard exposure events or scenarios with judgments of probability and consequences
A review of potential needs based on a risk assessment.
When loading low vapor pressure materials with high flash points into containers that may contain flammable vapors from previous cargoes, such as transferring diesel fuel into a tank truck that previously carried gasoline, there are significant fire hazards For more detailed information on the static ignition risks associated with this practice, refer to API 2003.
Defined by NFPA 750 as a water spray for which average water droplets are less than 1000 microns at the minimum design operating pressure of the water mist nozzle
4 Chemistry and Physics of Fire—Special Considerations
Chemistry and Physics of Fire
The processing, handling, and storage of petroleum products pose significant hazards due to their volatility Without proper precautions to manage these volatile components, there is a risk of fire or explosion, which can endanger personnel, damage equipment, and harm the environment.
Personnel engaged in refinery fire protection must understand fundamental combustion principles For detailed insights into the properties and dangers of petroleum products, as well as the chemistry and physics of fire, Annex A serves as a valuable resource for review and training Additional fire prevention and protection strategies to address these hazards are outlined in other sections of this publication and referenced materials.
Special Situations, Considerations, and Hazards
Hydrocarbon materials processed in refineries possess unique hazards associated with their storage, which can lead to significant risks Key phenomena, such as boilover, slopover, frothover, and boiling liquid expanding vapor explosion (BLEVE), can result in substantial damage.
Recognizing and addressing hazards is crucial in fire prevention design and emergency response planning Implementing operational precautions, as recommended, along with a well-structured emergency response plan, can significantly lower the chances of incidents and mitigate escalation during emergencies.
5 Fire Considerations in Refinery Design
General
This section outlines essential design principles for refineries, focusing on fire prevention and mitigation strategies It is important to note that this is not a design manual; rather, it serves as a guide to good engineering practices For detailed design information, readers are encouraged to consult the referenced materials.
When designing new refineries or upgrading existing ones, it is crucial to consider specific principles aimed at minimizing fire risks and mitigating potential fire damage Deviating from these principles does not automatically indicate inadequate fire protection Each project's safety and fire protection measures should be assessed based on experience, established process safety management practices, standard industry practices, and regulatory requirements.
Hazard Analysis
Preventing and mitigating the loss of containment of flammable and combustible materials is crucial for refinery fire protection Conducting systematic hazard analyses and implementing their findings can help refineries avoid significant process material releases and lower fire risks These efforts also support the implementation of corporate Management of Process Hazards programs and ensure compliance with regulatory requirements, such as OSHA 1910.119 and the EPA Risk Management Program Rule Additionally, a fire hazard analysis (FHA) provides a comprehensive assessment of fire protection needs, distinguishing it from a preliminary hazard analysis (PHA).
NOTE In-depth FHA discussions relevant to refineries can be found in some bibliography references such as AICHE-CCPS’s
Guidelines for Fire Protection in Chemical, Petrochemical and Hydrocarbon Processing Facilities However, many published FHA protocols focus on structural fires and are less relevant to process facilities.
Incorporating hazard analysis (PHA) during process design, site selection, and refinery layout is crucial for identifying potential fire hazards By considering preventive and mitigative safety measures early in the design stages, including during upgrades and expansions, the risk of incidents can be significantly reduced Input from research and development teams, designers, and refinery management is essential for a comprehensive hazard analysis The primary goal is to detect potential hazards early in the design process and to implement protective measures that effectively address these risks.
The analysis must assess the fire, internal explosion, and reactivity risks of process equipment and their contents, along with the potential consequences of these incidents A Fire Hazard Analysis (FHA) is essential in determining preventive measures and strategies to mitigate the impacts of such events.
Various PHA hazard analysis methodologies are widely utilized, including What If, Hazard and Operability Studies (HAZOP), Failure Mode and Effects Analysis (FMEA), and Fault Tree Analysis The AIChE-CCPS (Center for Chemical Process Safety) provides essential Guidelines for Hazard Evaluation.
Procedures and now has over 100 process safety resources listed in their catalog In the United States, OSHA PSM
1910.119 and EPA RMP provide additional information on these methodologies and provide technical guidance resources on their respective websites Similar regulatory resources are available in other jurisdictions.
Fire prevention and protection professionals must understand that a process hazards analysis differs from a fire protection analysis A well-conducted process hazards analysis can pinpoint potential fire-related events that need additional examination To determine the necessary level of protection for facilities and equipment, a Fire Hazard Analysis (FHA) is employed This study assesses the significance of fire hazards in specific areas and evaluates the consequences of fire-related incidents The findings from the FHA are incorporated into a comprehensive assessment process to evaluate risk and the cost-benefit trade-offs for hazard mitigation.
An FHA must inventory hazardous materials, assess the scale of potential fire scenarios, and evaluate their possible effects on personnel, equipment, the community, and the environment This documentation is essential for understanding fire hazards and enabling the development of effective performance-based fire protection solutions.
Process Design
Process design involves assessing the characteristics of materials, conditions, and inventories involved in a process It is crucial to prioritize "inherent safety" principles during this phase For instance, reducing the inventory of hazardous materials can significantly mitigate the potential impacts of leaks or explosions.
A fundamental grasp of the materials involved in a process is crucial, encompassing their general properties like reactivity, flammability, toxicity, and stability Additionally, it is essential to be aware of the safe handling procedures for these materials, particularly during storage.
When evaluating process conditions, it is crucial to comprehend the design's intended operating parameters, including pressure and temperature, as well as their safety margins Abnormal operating conditions that surpass these design limits can introduce significant hazards Such extremes can elevate stress levels, reduce material strength, and potentially lead to unwanted chemical reactions or equipment failures.
Equipment Design
Effective design and organization of equipment in processing, storage, and loading/unloading areas are crucial for preventing fire hazards Adhering to industry codes and standards, along with sound engineering practices by knowledgeable personnel, is essential Key design considerations include the choice of construction materials, mechanical design, equipment construction, and the process control system The following examples illustrate important conditions and mechanisms to consider.
Fires or explosions can be triggered by several conditions, including vapor clouds from flammable liquids or gases, spills from overfilled tanks, and excessive pressure in vessels that exceed their design limits Additionally, the loss of inerting systems, temperature increases from unstable conditions, and the formation of flammable mixtures within equipment pose significant risks Mixing incompatible materials, dust explosion conditions, and excessive vibration or shock from process operations can also lead to hazardous situations Lastly, product release may occur due to freezing water in process piping dead-legs.
Material release from process equipment can occur through several potential mechanisms, including vessel rupture caused by pressure or flow demands exceeding relief capacity, brittle fracture, and failures of flanges, gaskets, seals, or plugs Additionally, weld or casting failures, excessive corrosion or erosion, external loading or impact, internal explosions, and tube ruptures from overheating can also lead to material release.
The suitability of materials used in a refinery significantly impacts the risk of fire loss It is essential to consult and apply the standards and specifications set by nationally-recognized authorities, particularly those established by the American Petroleum Institute (API) to address the specific needs of oil refineries Additional resources can be found in publications from organizations such as the American Society for Testing and Materials (ASTM), the American Society of Mechanical Engineers (ASME), the National Fire Protection Association (NFPA), the American Society for Metals (ASM), the National Association of Corrosion Engineers (NACE), and Underwriters' Laboratories, Inc (UL).
Thorough material selection by qualified personnel significantly reduces the risk of material failure This process necessitates a deep understanding of internal processes, external environments, failure modes, appropriate material applications, fabrication techniques, maintenance strategies, and inspection schedules Implementing Positive Material Identification (PMI) programs serves as an effective quality-control measure to prevent the accidental use of unsuitable materials, thereby mitigating one of the key causes of material failures For instance, PMI programs can incorporate training focused on recognizing and identifying questionable or potentially counterfeit bolts.
Corrosion frequently results in the loss of containment of flammable and combustible materials, which can lead to fires Consequently, the risk of unforeseen corrosion is a critical consideration when choosing construction materials and implementing monitoring programs For guidance on the internal and external inspection of refinery equipment, refer to the relevant API publications listed in the bibliography.
The selection of materials is primarily based on their performance under specific process design conditions and their interaction with the external environment Key operating conditions to consider include start-up, shutdown, and upset scenarios Potential issues related to specific materials should be addressed during hazard analysis discussions Consulting personnel with relevant expertise is crucial during the material selection process.
5.4.3 Mechanical Design and Equipment Construction
Refinery processes often involve high pressures and temperatures, which can strain equipment Therefore, it is essential for the equipment used in these processes to be engineered to endure the demanding operating conditions.
A robust quality control program for equipment construction is essential to ensure that the "as-built" construction aligns with design specifications, complementing the quality control measures for materials.
Design and construction specifications for vessels subject to pressures of 15 psi gage or more are given in ASME Boiler and Pressure Code, Section VIII: Unfired Pressure Vessels
When inspecting a vessel internally, it is essential to ensure proper cleaning and ventilation The vessel should be isolated from other equipment and any flammable, toxic, or inert materials To mitigate potential pyrophoric residue concerns, appropriate precautions, such as water washing, should be implemented if the vessel is inerted.
Reactors, columns, exchangers, and boilers are typical pressure vessels found in a refinery that require special design considerations for structural supports, instrumentation, and protective systems.
To ensure safety and efficiency in vessel design, it is crucial to eliminate areas where water or hydrocarbons can accumulate, especially during start-up Strategically placing vent piping prevents bypassing and facilitates the effective removal of trapped condensable gases, thereby reducing the risk of water or light hydrocarbons remaining in the equipment Additionally, the rapid generation of steam from hot-oil charge stocks contacting water can lead to hazardous overpressure situations Retained hydrocarbons pose significant fire and industrial hygiene risks, making proper internal design essential.
Vessels that contain internal refractory or insulation, or those managing materials solely in vapor form, risk rapid overheating and rupture during a fire without proper passive fireproofing, active fire protection cooling, insulation, or a vessel depressuring system Additionally, vessels with two phases or tanks holding flammable liquids can also overheat if fire protection cooling measures or sufficient distance separation are not implemented.
Flanged connections on vessels should be positioned as near to the vessel as possible to facilitate isolation During the design and installation phases, it is essential to ensure that access to the flanges for blinding is taken into account Additionally, valves must be strategically placed to enable the opening of flanges for the installation and removal of isolation blinds.
To enhance safety in process vessels containing large volumes of flammable liquids, it is advisable to install block valves on connections below the liquid level This setup allows for the immediate shutoff of fuel flow in the event of a fire affecting downstream piping or equipment These manual or remote valves serve as a vital "second line of protection," complementing the primary safety measures achieved through effective design and operational practices.
Isolation valves are crucial for minimizing hydrocarbon release and preventing the influx of materials from other areas during emergencies They should be strategically placed at unit boundaries or within process units to isolate equipment in fire situations Safe access and the ability to manually operate these valves during emergencies must be considered Ideally, battery limit valves should be positioned away from fire hazardous areas to ensure safe manual actuation, while those located within such areas may require remote operation capabilities.
Location
The ideal location for a refinery should provide sufficient space for safe facility spacing, buffer zones, and future expansion It is crucial to assess the nature and proximity of adjacent properties, as they may expose the refinery to various hazards Additionally, potential hazards from neighboring properties, such as airports and their landing patterns, must be considered when determining the refinery's location and layout.
Natural disasters like windstorms, floods, and earthquakes pose significant fire hazards that must be considered in refinery system design Areas prone to earthquakes necessitate specialized equipment bracing, while regions experiencing extreme cold and heavy snowfall require unique designs to prevent equipment failure from freezing or excessive snow and ice loading, which can lead to additional fire risks For further details, refer to sections 8.4 and Annex B.
When designing facilities that may release flammable or toxic materials, it is crucial to consider prevailing wind conditions for effective siting and emergency response planning Awareness of seasonal variations in wind direction can significantly reduce the risk of ignition or exposure Utilizing wind socks can aid in assessing conditions during a release, but they must be properly maintained to ensure functionality, as they may become ineffective if frozen or unlit at night.
Ensuring an adequate supply of fire water and process water from various sources—whether internal, industrial, municipal, or natural—is crucial for refinery operations and emergency preparedness For more information on water supply, refer to sections 6.2 and 5.10.4.
Investigating the resources and availability of local public and private fire departments is essential, as well-equipped public fire departments can provide valuable assistance However, these departments typically lack training in combating large petroleum fires, making the sharing of training facilities and experiences mutually beneficial Additionally, exploring mutual-aid organizations, including nearby refineries or allied plants, is crucial, as they often possess specialized industrial equipment that has proven effective in emergency situations The presence of these organizations can significantly impact the necessary private fire protection equipment and staffing levels Notably, in some regions, a nonprofit industrial firefighting group is collaboratively owned by industry members, enhancing collective firefighting capabilities.
Layout
The layout of equipment in a refinery is influenced by topography, the types of units and equipment, and the operating methods of the company When designing the overall layout from a fire protection perspective, it is crucial to consider the location, spacing, and arrangement of all facilities to ensure safety and efficiency.
To minimize personnel exposure during a fire or explosion, new facilities must be strategically arranged Section 5.6.4 addresses building location and cites API 752 and CCPS’s Guidelines for safety.
Facility Siting and Layout Additional references are included in the bibliography.
The layout must ensure accessibility for firefighting and facilitate area isolation to inhibit fire spread within a unit It is essential to prioritize the accessibility of unit isolation block valves and valves for deluge, water spray, or sprinkler systems Additionally, remote shutoff or actuation valves should be considered for emergency response, particularly when accessing manual valves could expose personnel to hazardous conditions.
When planning installations, it is essential to assess the potential impacts on neighboring facilities, including communities, adjacent industries, public roads, and storage tanks Additionally, the planning process should incorporate provisions for future expansions to ensure comprehensive development.
The rectangular or block layout for process units offers significant benefits, including the ability to accommodate off-site process piping, service lines, and fire main systems This design allows for future expansions with minimal disruption to ongoing operations Additionally, the roadways between blocks serve as effective fire breaks and enhance the movement and operation of firefighting equipment, as further detailed in Section 5.6.5 regarding road access considerations.
When planning a new refinery layout or expansion, it is crucial to prioritize fire prevention Effective drainage systems are necessary to contain major spills and manage surface drainage, refinery waste, and fire water Utilizing the natural slope of the land can enhance the drainage system's effectiveness, and storage facilities should ideally be positioned downhill from process areas Additionally, incorporating windstorm and flood data, along with potential fire water usage, is essential for determining the appropriate capacity requirements for the drainage system.
The layout of equipment in a refinery is influenced by the process unit type, materials handled, design philosophy, and operational methods Key factors in planning this arrangement include safety, environmental impact, constructability, cost-effectiveness, and the efficiency of both process and maintenance operations.
When determining the spacing between process units, it is essential to consider factors such as fire radiation exposure, potential explosion overpressure, and access for firefighting equipment Additionally, maintenance needs for one unit while another is operational, including unrestricted hot work, must be evaluated The potential for business interruption and the relative value of the units involved, along with prevailing wind direction and access for construction and maintenance, are also critical considerations.
When determining the distance between the storage of flammable and combustible liquids and process areas, it is essential to consider factors similar to those for spacing between process units Tank dikes serve as the primary defense against spills reaching process units Ideally, process areas should be situated on higher ground than tank storage to mitigate the risk of spills, frothovers, or boilovers affecting the process area For more details, refer to Section 3 for definitions, Section 5.6.8 for equipment spacing outside process units, and NFPA 30 for minimum storage tank spacing requirements.
When determining the separation distances between liquefied petroleum gas (LPG) storage and processing areas and adjacent zones, it is crucial to consider the potential risks An incident, such as a release or explosion in a storage area, can generate overpressure that may inflict damage hundreds of feet away For detailed spacing guidelines, refer to API 2510 and NFPA 58.
To enhance safety, it is essential to separate buildings not involved in hydrocarbon processing from areas where hydrocarbon handling occurs, such as storage and loading facilities However, some process plant buildings may need to be situated near these areas for effective unit surveillance, maintenance, and emergency process control For managing risks related to these buildings, refer to API 752 and API 753, which offer guidance on the placement of both permanent and portable process plant structures Additional resources can be found in the references and bibliography of these standards.
Effective road design is crucial for fire protection in refinery operations, ensuring that all areas are accessible to emergency vehicles Roads must be sufficiently wide to facilitate the positioning and movement of these vehicles Additionally, any roads located within 25 feet of process equipment, intended solely for emergency or occasional maintenance access, should be marked as "restricted." Access to these restricted roads must be granted by operations only after the completion of hot work permitting procedures.
In emergency situations, it is essential to have multiple access routes to each refinery area Adequate turning radii must be incorporated to ensure that mobile equipment can navigate around pipe supports and other installations Additionally, pipe racks and crossings should be designed with sufficient overhead clearance to accommodate emergency vehicles and other traffic.
Well-drained roads in tank fields are essential for emergency response access, with adequate turnouts for equipment In flood-prone areas, slightly elevated roads may be required Prefire planning for storage tank zones must account for the accessibility of fire trucks and high-capacity foam monitors.
The location of public or private main roads relative to process equipment should be considered because motor vehicles can be ignition sources.
To ensure personnel safety, it is essential to provide adequate means of egress from all buildings and elevated structures, considering the specific hazards present Key principles include offering a sufficient number of exits, arranging them for safe emergency egress, and designing them according to the associated risks Additionally, egress paths must remain unobstructed and exits should be clearly marked and well-lit Fire alarms should be installed in areas where fires may not be immediately apparent, and all measures must comply with relevant codes and regulations.
Fireproofing
Effective fire safety in equipment placement requires not only strategic location and spacing but also additional protective measures A crucial aspect of fire protection is ensuring that equipment and its support structures can withstand fire conditions Fireproofing serves to enable emergency shutdowns, limit fuel addition to fires, and safeguard personnel and equipment from failures during a fire For comprehensive guidelines on fireproofing in hydrocarbon processing and storage, refer to API 2218 However, it is important to note that fireproofing can increase weight and potentially hide corrosion issues, with specific requirements varying by jurisdiction, especially for LPG vessels.
Pressure Relief and Flare Systems
For effective pressure-relieving system design, consult API 520, API 521, and API 2000, while flare facility design is covered in API 520, API 521, API 537, and section 5.8.3 Safety valve installation requirements, including set pressures and valve arrangements, are outlined in the ASME Boiler and Pressure Vessel Code, Section VIII: Unfired Pressure Vessels This article will focus on design challenges related to fire and explosion risks in pressure-relief and flare facilities.
Safety-relief valves are essential for preventing overpressure in refinery equipment during emergencies caused by operational errors, equipment failures, or fires, while ensuring safe disposal of released materials When block valves are installed adjacent to relief valves, they must be secured in the open position during operation Liquid hydrocarbon relief valves should discharge into a closed disposal system, whereas hydrocarbon vapor can be vented to the atmosphere if specific conditions are met, including maintaining safe distances from personnel, adhering to environmental regulations, ensuring low toxicity, keeping temperatures below autoignition, and considering the dispersion of released materials based on their physical properties.
Safety relief valves must undergo testing at regular intervals to ensure they operate at the specified pressure The testing frequency can range from several months to several years, influenced by factors such as service cleanliness, operating conditions, previous inspection results, and legal requirements Each valve's test schedule should be determined based on operational experience, engineering judgment, and industry standards (refer to API 576) In facilities where block valves are positioned below relief valves, it is often mandated that these block valves remain car-sealed or locked open during operation If a pressure relief valve (PRV) needs to be removed for testing or maintenance, equivalent overpressure protection must be in place while the unit operates, and typically, a replacement valve is installed before reopening the system.
When routing relief valve discharges to a closed system, it is crucial to size headers to accommodate the maximum flow from any single contingency while preventing excessive back pressure on the connected relief valves The arrangement of safety relief valves within a closed emergency relief system can affect the necessary size of the relief facility piping, particularly when equipment is grouped in a single fire risk area Implementing adequate separations between equipment groups can minimize the volume of materials released into flare systems during fire incidents Additionally, fire-related electric power failures should be considered in the contingency analysis for flare systems.
To prevent issues such as plugging, blocking, or freezing, it is essential to design piping systems without "pockets" and ensure they are sloped toward liquid knockout drums This design minimizes the risk of liquid accumulation, which can lead to surging and other operational problems.
In a closed emergency relief system serving multiple units, it is essential to isolate specific sections when individual units are shut down Thus, it is crucial to assess the availability of proper facilities for blinding or isolating these units Additionally, when isolating a unit, it is important to ensure that the overpressure protection for other units complies with the relevant API or ASME standards.
To prevent localized overheating of nearby process vessels during a fire or abnormal conditions, safety-relief valves must discharge to vent stacks that terminate above adjacent equipment This ensures that any released vapors do not pose a risk of ignition or heat transfer to surrounding areas.
Proper drainage design for the discharge risers of atmospheric safety valves is crucial to minimize potential issues Clogged drains can lead to the accumulation of condensed hydrocarbons from leaking safety valves, which may be expelled if the valves activate This poses a fire risk if the accumulated material encounters an ignition source.
Water accumulation in the vent stack can lead to freezing, which may happen due to low ambient temperatures or the refrigeration effect from the rapid evaporation of leaking low boiling point hydrocarbons.
Drains must be positioned at the base of the riser, ensuring proper orientation to prevent burning vapor from affecting nearby equipment during fire conditions Installing elbows in the drain can effectively redirect any released vapor away from adjacent vessels or piping, minimizing potential hazards.
Vent stacks that discharge at elevated locations are sometimes equipped with snuffing steam to extinguish fires caused by lightning ignition of relief valve leakage See API 520 for additional information.
Flare systems, as outlined in API 521 and API 537, are essential for the safe disposal of gaseous refinery wastes These systems are utilized based on local environmental regulations for various purposes, including venting during start-up or shutdown, managing excess refinery gas, and handling emergency releases from safety valves, blowdown, and depressuring systems.
Designs differ significantly based on the type of connected equipment and the overall system's complexity While this publication does not delve into specific design details, it highlights several potential problem areas to consider.
Flare systems, being open to the atmosphere and having a continuous ignition source, pose a risk of internal explosions without proper safeguards To mitigate this hazard, it is essential to thoroughly purge the system of trapped air before igniting the pilots Additionally, safe lighting methods should be implemented, such as using electrical ignitors or ignition pipes that allow flammable mixtures to propagate the flame to the pilots.
To prevent air from entering flare systems, it is essential to avoid vent connections or bleeders While completely eliminating air may not be feasible, minimizing risks can be achieved by continuously injecting a fuel-gas purge or installing liquid seals as flashback devices to restrict flame propagation Liquid seals are preferred over flame arrestors, as the latter can become fouled, leading to excessive pressure drops during high flow When designing purging systems, it is crucial to account for potential air ingress from the flare stack, especially when using lighter-than-air purge gases Additionally, dry molecular seals can help reduce purge gas rates.
Concerns arise regarding the potential for liquid carryover from flare stacks, which could result in the spraying of burning liquid over a large area and ignite fires at ground level The dimensions of knockout drums should be determined by the equipment discharging into them, the rates of liquid entry, the duration of any release, and the routing of blowdown or liquid pumpout streams to the flare stacks Establishing an exclusion zone beneath flares is standard practice to safeguard personnel and facilities, primarily due to thermal radiation risks.