Storage Tank Categories: API RP 2350 Definitions

With the American Petroleum Institute’s API RP 2350 fourth edition guidelines having been updated earlier this year, tank storage facility operators are using the recommendations to safeguard against potential life- and environment-endangering overfill accidents. One aspect operators need to understand is tank categories, upon which overfill prevention methodologies are based.

API 2350 Guidelines

API 2350 categorizes storage tanks by the level of staffing present during receiving operations.

Category 1 – Fully attended

  • Personnel must always be on site during the receipt of product, must monitor the receipt continuously during the first and last hours and must verify receipt each hour.
  • Level instrumentation is not required but may be used. Output will be local only. Alarms may be point or continuous level devices.
  • Termination of receipt is done manually by site personnel or by the transporter as instructed by site personnel.

Category 2 – Semi-attended

  • Personnel must be present during the initial and final 30 minutes of the receipt. The transporter must assist in monitoring the high-high (HH) alarm.
  • Tanks must be equipped with an automatic tank gauge system (ATGS) with a transmittable output signal. The level sensor may be continuous or point. For maximum redundancy, it should be of a measurement technology different than that of the ATG.
  • The control center has the ability to terminate receipt.

Category 3 – Unattended

  • Personnel are not required to be present during receiving operations but are remotely located at a control center. The transporter must monitor the both level and HH alarm.
  • Tanks must be equipped with an ATGS consisting of a level sensor and independent HH sensor. The output of both instruments must be transmitted to a control center in ‘real time.’ The level sensor may be continuous electronic or point mechanical or electronic. Sensors with self-diagnostics are preferred.
  • The control center has the ability to terminate receipt. In addition, the HH sensor must automatically terminate flow to the tank or alert the transporter to terminate receipt. Failure of the ATGS must also terminate flow.

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