Tank Overfill Prevention – Are your tanks spill free?

  • Post published:July 21, 2017

Are your generators, vehicles, plant equipment or stationary tanks overfilling? There are numerous ways to manage the risk of tank overfill, and in this blog article, we’ll lay out some of the most common, along with the pros and cons of each.

Are your generators, vehicles, plant equipment or stationary tanks overfilling?

Your first question is probably ‘Why should I care?’, and you’d be asking the right question. It all comes down to risk; what is going to happen in each specific situation if an overfill occurs? Does your current risk management program consider the variables of each application, specifically those variables which may determine a hazard? The ALARP principal is often used in the regulation or safety-critical systems, and requires that residual risk is reduced “as low as reasonably practicable”.
If you overfill a small storage tank used for water, it may be that plants will get watered, and ‘people could get wet’.
With liquid hydrocarbons, it’s often more of an issue. Soil and water become contaminated, tanks are ruptured, critical machines burn down, explosions occur; people can die.

There are numerous ways to manage the risk of tank overfill, and in this blog article, we’ll lay out some of the most common, along with the pros and cons of each.

tank overfill prevention infographic banlaw

Float valve systems

Float Valve Systems are very common, typically as the first (primary) means of tank overfill prevention (OFP). Fluid enters the tank through a valve that has a cantilever (or similar) float attached. As the level rises, the fluid path is blocked.


  • These entry-level systems are cost efficient, particularly for stationary small to medium capacity liquid storage tanks


  • As the fluid level rises the valve can close incrementally. Often, by the time the tank is within 30% of the safe fill level (SFL) flowrates are being throttled, wasting precious time during every fill
  • Pressure builds up behind the closed overfill prevention valve, and the operator will typically need to shut off the supply pump manually. Failure to shut off the pump shortly after the valve closes can introduce additional hazards to the tank filling process
  • Often these overfill prevention valves are ‘hidden’ from view within the tank. Do you know where it is? When was the last time you inspected the valve, and performed the routine inspection and testing guidelines stipulated by the valve OEM?

Audible or visual alarms

Audible/visual alarms are a means of indicating that the primary overfill protection system has failed.


  • Alerting the operator that the primary overfill protection system has failed, allows them to quickly turn off the pump and avoid, or minimise the tank overfill


  • This solution relies on the refilling process being constantly supervised by an operator, ready to act in the event the tank alarm is activated
  • The device itself does not stop fluid from entering the tank, or the tank from overfilling. An ‘alarm’ is only effective if it is responded to within the required timeframe
  • Tank overfill alarm devices require electricity or other means of powering them

Other mechanical overfill protection systems

Modern mechanical tank overfill prevention systems are ‘powered’ by the flow of fuel into the tank. A level sensor identifies when the tank is full, and causes a control valve located before or at the tank entry point to block the fluid path.


  • Cost efficient
  • Readily adaptable to a wide range of stationary and mobile small to medium size diesel engine running tanks, and smaller bulk storage tanks
  • No wiring or electricity is required
  • Improved reliability over cantilever-style float systems, which suffer from wear and tear, especially in mobile applications
  • Banlaw’s unique (patents pending) level sensor design also provides improved level-accuracy, and quick actuation. This means diesel tanks can be filled closer to their SFL with no throttling of flowrates
  • Banlaw’s more efficient (patents pending) flow control valve design provides higher refilling flowrates with reduced incidence of ‘premature shut-off’, of pressure-activated refuelling nozzles


  • A secondary tank overfill prevention methodology should still be employed for redundancy
  • Typically, only suitable for use with low viscosity liquids, e.g. diesels
  • Susceptible to contaminated fuel – fuel contamination levels need to be maintained within diesel engine OEM specifications, and/or industry governances and guidelines (e.g. World-Wide Fuel Charter)


Stand-alone electronic non-safety rated systems

Stand-alone electronic overfill protection systems
provide heightened risk management for critical machines. A high-level float switch (sensor) communicates with a logic solver (control unit), which then actuates a flow stop end-element such as a pump or ball valve.


  • These electronic systems are completely independent, and can be deployed on-board a vehicle or other equipment
  • They allow for the integration of fire safe (e.g. API 607) valves and other fire-retardant technologies to help mitigate the discharge of fuel from the tank in the event of a fire.
  • Fire suppression systems on-board plant equipment are unlikely to control a fire in the event that fuel within the tank escapes
  • Normally-closed ball valves ensure the only time fuel can flow into or out of the tank is during refuelling
  • These systems are completely unrestricted by flowrate, allowing for the highest refuelling speeds to be achieved
  • They can also be used with many diverse types of fluids


  • Power is required (12/24VDC)
  • Can be more expensive than mechanical overfill protection systems
  • The OFP function is often jeopardised in the event of a power failure
  • Systems can be designed to ‘fail to a safe state’

banlaw's 'fillsafe' stand-alone electronic and mechanical tank overfill protection systems
(Banlaw’s ‘FillSafe’ stand-alone electronic and mechanical tank overfill protection systems)


Integrated electronic non-safety systems

Integrated electronic tank overfill prevention systems combine OFP functionality with other tank gauging or fuel management system capabilities. The flow of liquid is ceased by using a level sensor (e.g. ultrasonic, guided wave radar etc.) to identify when the tank has reached its SFL. The level sensor interacts with a controller unit, which then turns off the supply pump or actuates a valve to close.


  • This is the first step in integrated remote asset management
  • Can be deployed as a stand-alone system
  • Allows for local tank level display
  • Interfaces with online Fuel Management System (FMS) software suites


  • Requires power
  • Requires a communications link if it is to interface with a fuel management software solution
  • More expensive than systems dedicated to tank overfill prevention alone

banlaw's fuel management controllers, with ofp, atg, and fms functionality options
(Banlaw’s Fuel Management Controllers, with OFP, ATG, and FMS functionality options)

Electronic safety rated systems

Electronic safety systems – Safety Instrumented System (SIS) – are the last line of defence in bulk storage overfill protection. These systems provide a final layer of protection in the process, and decrease the probability of tank overfill. Facilities that follow a safety lifecycle management structure are likely to have less operational ‘challenges’. The structure itself helps guide Management and operators in the day to day operation of the facility. Fuel farms often employ two or even three layers of protection in the overfill protection area, especially in ‘unmanned’ operation scenarios where a person is not specifically overseeing the tank being filled (i.e. unsupervised refilling). A SIS is typically designed to be the last (emergency) layer of defence against OFP, and is not intended to act as the normal (routine) OFP system. It is used to reduce the risk of accidental overfilling if all other layers fail to shut down the system in a safe manner.

SIS’s are designed to achieve the required SIL rating. The SIL rating is determined by a SIL Hazard operational assessment of the specific OFP application, considering a wide array of assessment ‘inputs’ to achieve the required SIL rating of the SIS. Each sub-system of the SIS must have a minimum SIL rating to meet the safety requirement specification (e.g. SIL-1, SIL-2, etc). Such components may include; a ‘high-high’ level sensor, logic solver/controller, actuated valve, and/or means to shut-off the fluid supply into the tank(s) by using pump control. These systems include feedback to ensure that components are ‘healthy’, and that in the event the SIS is activated, alarms are raised to alert personnel of a major failure of the lower tier OFP systems. SIS hardware is also designed to fail to a ‘safe state’ should it ever do so. Electronic safety systems are deployed as a separate safety system layer, providing complete redundancy.


  • Absolute assurance that tank overfill and associated ruptures, machine damage, and operator safety issues are avoided
  • Heightened control of the reliability of the installation


  • An extra layer of safety represents an extra layer of cost
  • Complexity is increased
  • There are also requirements for routine testing of safety systems as part of preventative maintenance processes

Not sure what you should choose?

There is seldom a ‘one size fits all’ approach. Appropriate due diligences and effective change management must govern the initial design of an OFP system, and any changes to that system or where/how the system is used. Further, few (if any) OFP systems are maintenance free, and OEM/designer preventative and corrective maintenance guidelines should be followed.

The correct overfill protection framework for tanks and machines that you manage comes down to an application-specific assessment of risk. The following is a list of which Banlaw technologies tend to be most suitable for different use cases.

FillSafe Zero is a ‘pressureless’ mechanical tank overfill prevention system. Small to medium sized tanks and vehicles can be filled with diesel at up to 1000lpm (264gpm). Importantly and unlike many other competitor systems, the functionality of automatic shut-off ‘pressurised tank’ dry break refuelling hardware is also preserved as a backup (i.e. secondary protection layer, of OFP).

FillSafe Power is a stand-alone electronic tank overfill prevention system. It is used for critical machines such as mining excavators where fire safe installation and productivity gains from superior refuelling speeds are especially important.

banlaw tank overfill prevention systems for each machine type

Banlaw’s FuelTrack and ResTrack Fuel/Asset Management Systems are used to deliver bulk tank gauging, fuel management, and resource management facility safety solutions. Capabilities cover those mentioned in this newsletter around tank OFP, and much more.

banlaw overfill prevention bulk storage tanks
To learn more about the importance of performing site-specific risk assessments, and installing bulk storage overfill protection: Watch this video by the U.S. Chemical Safety Board.https://youtu.be/41QMaJqxqIo


Click below for more details

FillSafe Zero (mechanical tank overfill prevention)

FillSafe Power (electronic tank overfill prevention)

Fuel Management Systems