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API Publication 2021 (1991): Management of Atmospheric Storage Tank Fires – Scope and Technical Requirements
A comprehensive guide to fire prevention, control, and emergency response for atmospheric storage tanks according to the 1991 edition
Scope and Historical Context
API Publication 2021 (1991), commonly referred to as API Publ 2021-1991, is a foundational document issued by the American Petroleum Institute that addresses the management of fires in atmospheric storage tanks. This publication was developed to provide the petroleum industry with a structured approach to preventing, controlling, and extinguishing fires that may occur in fixed-roof, floating-roof, and other atmospheric storage configurations.
The 1991 edition consolidates decades of operational experience and incident analysis, offering engineering guidelines rather than rigid specifications. It covers facilities that store flammable and combustible liquids at or near atmospheric pressure, with a particular focus on refining, petrochemical, and bulk terminal installations. Although superseded by later revisions (2001, 2006, etc.), the 1991 version remains an important reference for legacy system evaluations and training programs.
Scope Note: API Publ 2021-1991 applies primarily to aboveground storage tanks (ASTs) used in hydrocarbon service. It does not cover pressurized or refrigerated storage vessels, which are addressed in separate API standards.
Technical Requirements and Recommendations
Fire Prevention Measures
Effective fire management begins with prevention. The 1991 edition outlines key design and operational practices, including proper dike and drainage design, secondary containment, and maintenance of seals on floating roofs. It emphasizes the control of ignition sources through grounding, bonding, and hot-work permitting systems. Routine inspection of tank appurtenances—such as gaskets, vents, and emergency relief systems—is also recommended to mitigate vapor leaks that could lead to fire ignition.
Fire Suppression Systems
API Publ 2021-1991 provides detailed guidance on selecting and installing fire suppression equipment. For fixed-roof tanks, foam systems remain a primary recommendation. The publication describes proper foam concentrate types (protein, fluoroprotein, and aqueous film-forming foam), application rates, and subsurface injection methods for flammable-liquid tanks. For floating-roof tanks, the focus is on rim-seal protection using either fixed or semi-fixed foam chambers or monitors.
| Suppression System | Applicable Tank Type | Key Features | Limitations |
|---|---|---|---|
| Fixed foam system (top pourer) | Fixed-roof (open-top cone or dome) | Dedicated foam line; high flow rate; automatic activation | High capital cost; foam damage from weather if not protected |
| Subsurface foam injection | Fixed-roof (flammable liquids) | Reduced vapor disturbance; can be retrofitted; effective for deep-seated fires | Requires high foam backpressure; limited to compatible liquids |
| Rim-seal foam chambers | Floating-roof (internal/ external) | Direct seal protection; low foam consumption; quick response | Limited to rim fires; requires proper seal maintenance |
| Portable monitors and hose streams | Any (supplemental) | Flexible deployment; low cost; provides cooling support | Manual operation; higher personnel exposure; limited flow capacity |
Important Consideration: Foam compositions and environmental regulations have evolved significantly since 1991. Users are urged to verify that the foam types referenced in the original publication comply with current environmental standards, especially regarding PFAS-containing foams.
Emergency Response Planning
Beyond hardware, API Publ 2021-1991 stresses the need for site-specific emergency response plans. It recommends establishing clear incident command structures, pre-incident planning with local fire services, and conducting periodic drills. The publication also discusses strategies for water demand estimation, foam concentrate inventory, and cooling-water application rates for adjacent tank protection.
Implementation and Compliance
Regulatory Integration
While API Publ 2021-1991 is a voluntary consensus standard, it has been incorporated by reference into various regulatory frameworks, including OSHR requirements for petroleum facilities in the United States and similar international counterparts. Compliance with the publication is often viewed by insurers and enforcement agencies as a benchmark of due diligence for fire management at storage terminals.
Best Practice: Facilities that align fire protection programs with API Publ 2021-1991 often experience lower insurance premiums and improved incident response outcomes. Regular audits against the standard help maintain operational readiness.
Auditing and Training
Effective implementation requires ongoing verification. The standard encourages facility operators to conduct periodic internal audits covering foam system testing, seal integrity inspections, and drainage valve condition. Operator training should include system activation procedures, recognition of fire hazards, and emergency shutdown protocols. Document retention of inspection results is also recommended to demonstrate continuous improvement.
Common Pitfall: Some facilities assume that installing a foam system fulfills all fire protection requirements. API Publ 2021-1991 emphasizes that suppression hardware must be part of a comprehensive management system that includes prevention, detection, emergency response, and post-incident review.
Conclusion and Modern Relevance
Though eventually superseded, API Publ 2021-1991 laid the groundwork for modern atmospheric storage tank fire management. Its systematic approach—spanning prevention, suppression, and response—remains a valuable template for training, system design, and regulatory compliance. Facilities using legacy systems that were designed in accordance with the 1991 edition should also consult current API standards (e.g., API 2021-2001/2006) to ensure their approach meets contemporary safety and environmental expectations.
Update Advisory: Operators referencing the 1991 scan should cross-check foam application rates and extinguishing agents with API 2021 (current edition) and NFPA 11 to account for technological advances and regulatory changes that have occurred over the past three decades.
Frequently Asked Questions
Q: What types of tanks does API Publ 2021-1991 cover?
A: The publication covers atmospheric storage tanks commonly used in petroleum and petrochemical operations, including fixed-roof, external floating-roof, and internal floating-roof tanks. It does not apply to pressurized spheres or refrigerated cryogenic storage vessels.
A: The publication covers atmospheric storage tanks commonly used in petroleum and petrochemical operations, including fixed-roof, external floating-roof, and internal floating-roof tanks. It does not apply to pressurized spheres or refrigerated cryogenic storage vessels.
Q: Is API Publ 2021-1991 still valid for current facility designs?
A: The 1991 edition has been superseded by later versions (2001, 2006, and subsequent revisions). While it is not considered current for new designs, it remains a useful reference for legacy systems, training programs, and historical incident analysis. Facilities should refer to the latest edition for up-to-date requirements.
A: The 1991 edition has been superseded by later versions (2001, 2006, and subsequent revisions). While it is not considered current for new designs, it remains a useful reference for legacy systems, training programs, and historical incident analysis. Facilities should refer to the latest edition for up-to-date requirements.
Q: Does the standard require foam suppression systems on all tanks?
A: No. The publication provides recommendations based on tank size, product stored, location, and other risk factors. It does not mandate a universal solution but guides the user through a risk-based decision process. Smaller tanks or those with low-hazard materials may rely on emergency response plans without fixed suppression hardware.
A: No. The publication provides recommendations based on tank size, product stored, location, and other risk factors. It does not mandate a universal solution but guides the user through a risk-based decision process. Smaller tanks or those with low-hazard materials may rely on emergency response plans without fixed suppression hardware.
© 2026 – Technical overview of API Publ 2021-1991. For authoritative compliance, consult the latest API publication directly.