This article outlines the minimum mandatory safety standards for the spacing and diking of onshore, above-grade storage tanks that handle flammable or combustible liquids at atmospheric pressure or up to 100 kPa(g) (15 psig), and at ambient or higher temperatures. It applies to various tank configurations, including vertical cylindrical tanks with fixed or floating roofs, horizontal drums, spheres, spheroids, and other designs that meet recognized engineering standards.
Scope and Applicability
This guideline is designed to enhance facility safety and environmental protection by specifying critical spacing and diking requirements for tanks storing hazardous liquids such as gasoline, diesel, and asphalt. Improper storage of such liquids poses serious fire, explosion, and environmental hazards.
The standard applies to permanent tank installations used in refining, processing, and storage operations, but excludes:
- Refrigerated or pressure storage vessels (covered under separate regulations)
- Skid-mounted tanks temporarily deployed at wellsites for drilling or workover operations
For tanks with a capacity of 190 m³ (50,000 gallons) or less, the spacing and diking requirements follow NFPA 30 (National Fire Protection Association Standard for Flammable and Combustible Liquids).
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Key Safety Requirements
1. Tank Spacing Guidelines
Proper tank-to-tank and tank-to-equipment spacing is vital to:
- Prevent fire spread
- Reduce incident escalation
- Control heat radiation and vapor dispersion
Spacing is determined based on:
- Tank configuration
- Type of liquid stored (flammable or combustible)
These distance requirements ensure safer tank arrangements and better access for fire protection systems.
2. Diking and Containment Requirements
Diking systems are required to:
- Contain spills or leaks
- Prevent contamination
- Control fire risk
For tanks over 190 m³, dikes must be:
- Sized to hold the entire contents of the largest tank within the diked area
- Constructed to resist hydrostatic pressure
- Liquid-tight to ensure complete containment
Smaller tanks follow containment requirements per NFPA 30. Facilities with proper oily water drainage or remote impounding may qualify for modified diking criteria.
3. Design and Construction Standards
Tanks must comply with internationally recognized standards to ensure structural integrity and safety, including:
- API STD 620 – Design and Construction of Large, Welded, Low-Pressure Storage Tanks
- API STD 650 – Welded Steel Tanks for Oil Storage
- API STD 2000 – Venting Atmospheric and Low-Pressure Storage Tanks
These standards guide materials selection, fabrication, pressure handling, and environmental resistance.
4. Exclusions and Exceptions
The following are outside the scope of this standard:
- Temporary, skid-mounted tanks at wellsites
- Smaller tanks (≤ 190 m³) located in process areas with engineered drainage systems
In such cases, alternative containment or spacing measures are permissible under defined safety protocols.
Commitment to Safety and Compliance
Implementing these spacing and diking standards is essential to:
- Minimize the risk of fires, spills, or catastrophic events
- Ensure compliance with NFPA and API guidelines
- Promote safe and sustainable tank farm operations
By adhering to these requirements, oil and gas operators demonstrate a proactive commitment to safety, regulatory compliance, and environmental stewardship.