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New API 2350 Overfill Prevention Standards: What You Need to Know About the Fourth Edition Update

In the wake of the Buncefield Oil Depot and other significant tank overfill incidents in recent years, the American Petroleum Institute has revised its API 2350 recommended practices to address malfunctioning or insufficient tank level gauging. While not mandatory, the API 2350 standards are being used by many facilities to improve tank storage safety. Here’s a quick summary of what you need to know about the new guidelines:


  • Applicability: Above ground storage tanks with capacities greater than 1320 gallons (5000 L) that store Class I, II or III flammable or combustible liquids, and that receive liquids from mainline pipelines or marine vessels.
  • Equipment: The Overfill Prevention System (OPS) typically includes an alarm signal system and allied support systems—shutdown or diversion valves, communications, sensors, and logic solvers. An OPS should be on an uninterruptible power supply.
  • Self-Diagnostics: Sensors with self-diagnostics are preferred for high-high (HH) level on an OPS.
  • Floating Roof Sensors: A sensor used on a floating roof tank must detect the roof, as well as the liquid if it covers the roof.
  • Management System: API RP 2350 recommends a formal approach to training and procedures that comprise an Overfill Prevention Process (OPP). This is a management system with formal operating procedures and practices, risk assessment, scheduled inspections, periodic testing, and equipment maintenance programs.
  • Proof Testing: All OPS equipment required to terminate receipt must be tested annually. The HH sensor/alarm must be tested semi-annually. The method of test-actuation is chosen by the operator and may include: moving the tank level; actuating a manual proofer device; initiating a wet probe test; or utilizing self-diagnostics or a push button self-test if the instrument is so equipped. When moving level to proof test, it is not recommended that the level be raised above the maximum working level.
  • Independence: A key feature of API RP 2350 is that the sensors and alarms used for HH tank level or any part of the AOPS may not be used for routine tank filling operations. In addition, the HH level sensor on Category III tanks must be independent from all other level sensors.
  • Redundancy: A common strategy for critical level detection is redundancy of the sensors. Ideally, redundant sensors will be of disparate technologies to avoid multiple failures due to application concerns.
  • Required Alarms: High-High Alarm (Category II and III); additional alarms and alerts at the owner/operator’s discretion.