Tank Ignition Source Management: Protecting Storage Tanks from Fires Due to Overfill

Tank Ignition Source Management: Protecting Storage Tanks from Fires Due to Overfill

By: Earl Crochet and Rafael Rengifo

Aboveground Storage Tanks (AST) are used to store large volumes of flammable and combustible liquids in refineries, tank farms, and terminals. When filling ASTs, it is important to keep the flammable or combustible products in the tank, to avoid fires and associated safety and environmental issues. 

Part One of the “Tank Ignition Source Management” series focused on protecting storage tanks from fires due to lightening strikes. Part Two will focus on protecting storage tanks from fires due to overfills.

Significant examples of what can happen when you don’t operate your tanks correctly and overfills occur are the Buncefield fire in the UK in December of 2005 (https://www.hse.gov.uk/comah/buncefield/index.htm) and the CAPECO fire in Puerto Rico in October 2009 (https://www.csb.gov/caribbean-petroleum-refining-tank-explosion-and-fire/).

To avoid overfilling tanks, one of the most used rules is to follow API Standard 2350, Overfill Prevention for Storage Tanks in Petroleum Facilities, 5th edition, published in September 2020.  API 2350 is a consensus document, written by people in the industry, and has been referenced as part of both federal and state regulations.

To comply with API 2350, an owner must implement an Overfill Prevention System, (OPS). From API 2350, an OPS must contain the following components:

·        Management system

·        Risk assessment process

·        Operational parameters

·        Procedures (including those for receipt termination) and training

·        Equipment supporting OPS and its inspection, testing, and maintenance.


Management System

At a minimum, the management system shall address:

        Formal documented operating procedures and practices, including safety and emergency response procedures

        Competency of operating and maintenance personnel

        Functional equipment systems, tested and maintained by competent personnel

        Scheduled inspection and maintenance programs for overfill instrumentation and equipment

        Systems and procedures to address both normal and abnormal operating conditions

        Management of change (MOC) process that includes personnel and equipment changes

        System to identify, investigate, and communicate overfill near-misses and incidents

        System to share lessons learned

        Follow-up system to address any needed mitigation of circumstances leading to near-misses or incidents

        Communication systems protocols within the owner/operator organization and between the transporter and the owner/operator that are designed to function under abnormal as well as normal conditions

        Periodic review and updating of management system for continuous improvement.

Risk Assessment Requirements

API 2350 allows an owner to perform a risk assessment based on their own preferences. The risk assessment can be qualitative or semi-quantitative (including LOPA).

From API 2350: “The owner/operator shall utilize the requirements in 5.2 where the categories (found in Annex G) are used with the associated response times found in 4.4.23 until a risk assessment is undertaken. For a tank that does not fit into a category, the owner/operator shall default to the next more conservative applicable category.”

The category system is based on the technology installed on the tank.  The easiest way to understand the different categories is:

Tank Category Technology on the Tank
0 None; no gauge, or alarms
1 Local gauge on the tank only
2 Local gauge on the tank that also communicates with a control room
3 Category 2 tank with an independent alarm


Defining Operating Parameters

The owner/operator shall establish and document the following Levels of Concern (LOCs) that are applicable for tanks covered by this standard:

·       Critical high (CH) level

·       AOPS activation level (if equipped with an AOPS)

·       High-high (HH) level

·       High (H) level (optional)

·       Maximum working (MW) level.

API 2350 has the detailed definitions of each of these LOCs. The response times for each tank will be determined in order to calculate each of the LOCs above.

Until these response times are validated by the owner, the minimum response times between maximum working/high-high levels and high-high/critical high levels shall be:

Tank Category Minimum Response Time
0 60
1 45
2 30
3 15


Procedures for Operations

Procedures shall include all the following:

·       Procedures for planning the receipt

·       Procedures for pre-receipt activities

·       Procedures for activities during receipt

·       Procedures for post-receipt activities

·       Procedures for emergencies and abnormal conditions

·       Procedures for training on overfill prevention systems

·       Procedures for testing, inspection, and maintenance of the equipment of an OPS

Each owner shall have procedures on inspection, maintenance and testing of all equipment used as part of the OPS.


Tank levels management requires a comprehensive / multidisciplinary approach in order to maximize the storage capacity while minimizing the risk of an overfill. The adoption of these Process Safety Management (PSM) elements to support tank operations is being implemented proactively by owner/users and also required by regulatory bodies.    

Stay tuned for Part 3 – “Protecting Storage Tanks from Fires Due to Static Electricity.”

Becht can help you assess your risks and avoid overfilling your tanks. Contact a Becht expert for more information.


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