Heating Oil Tanks: Overfill Prevention

Photograph of Carbery, Diamond and Harlequin Oil Tanks on an orange background

An overfill occurs when an attempt is made to deliver too much oil to a tank. Overfills can occur for a number of reasons. They’re one of the most frequent causes of oil-related, environmental pollution incidents today. The good news is that they’re also one of the easiest to prevent.

European Standard EN 13616 specifies 2 forms of overfill prevention systems – Type A and Type B. Both systems are designed to reduce the risk of an overfill occurring at a Heating Oil storage installation. Consistent with Oil Firing Technical Association (OFTEC) requirements, many tanks supplied in the UK and Republic of Ireland today incorporate either a Type A or Type B system.

Type A Mechanical Overfill Prevention Devices

Type A devices are a mechanically activated, overfill prevention valve (OPV) fitted to an Oil Tank’s Fill Point. When the level of Heating Oil inside the tank rises to the maximum permissible, the valve moves to the closed position, discontinuing the supply of Heating Oil to the tank. These devices have a number of benefits:

  • They’re affordable;

  • They’re suitable for use with almost any Heating Oil Tank – irrespective of manufacturer or material of construction;

  • They require little maintenance;

  • They’re stand-alone units and not dependent upon fuel deliveries being made from a compatible tanker.

Their biggest drawbacks is they are not always failsafe in operation. So, in the event of product failure, a Type A device may on very rare occasions cause the event it’s designed to prevent i.e. an overfill. Whilst instances of reported product failure are exceptionally rare, Type A devices can sometimes be easily bypassed on some makes and models of Heating Oil Tanks e.g. by delivering fuel via a tank’s inspection point. Additionally, Type A devices can sometimes prove difficult to retrofit to existing storage tanks.

Type B Electronic Overfill Prevention Systems

Type B Systems typically comprise a probe mounted electronic thermistor, fitted to the tank. When delivering fuel, delivery personnel attach an electronic transceiver unit to the probe. When the level of fuel rises inside the tank and makes contact with the probe, the thermistor detects a change in temperature. The transceiver unit then sends a signal to the tank, which switches off the fuel delivery pump and discontinues refuelling. Type B devices offer a number of advantages:

  • Unlike Type A devices, they are failsafe in operation. In the event of equipment failure, refuelling will be discontinued and a potential overfill prevented;

  • The tank mounted probe usually costs less than a Type A device;

  • The probes are sealed units and require little if any maintenance;

  • Probes can be quickly and easily fitted to almost any new or existing tank.

The biggest drawback of the Type B system is that to provide overfill protection during refuelling, fuel must be dispensed from a compatible tanker. Otherwise, whilst the tank can still be filled as normal, the risk of an overfill will remain.

Type B systems have been successfully used in the aircraft refuelling sector. They are also widely used in several EU countries, where overfills have all but been eliminated following their introduction. However, the lax regulatory environment in the UK and Republic of Ireland, combined with an unwillingness by many fuel distributors to prioritise investments in failsafe, electronic, overfill prevention technology, makes suitably equipped tankers are a rarity on British and Irish roads.

Overfill Warning Devices

Beyond Type A and Type B systems, a number of other systems and devices are available. These include audible and visual overfill warning alarms, together with handheld devices which operate in conjunction with oil tank contents gauges. Unlike Type A and Type B systems, these systems are not designed to prevent an overfill from occurring, but instead to sound an alert, allowing delivery personnel to cease refuelling before an overfill occurs.

When installed alongside either a Type A or Type B Overfill Prevention Device, overfill warning devices can help provide a ‘belt and braces’ approach to overfill prevention.

Do I need to fit an Overfill Prevention / Warning System?

Many Heating Oil Tanks are supplied with either a Type A or Type B Overfill Prevention Device as standard. However, under current regulations in the UK and Republic of Ireland, unless the vent point of the tank is not visible from the fill point and / or another site-specific hazard exists, there is generally no legal requirement to fit an overfill warning at most oil storage installations. That said, it’s certainly good practice to fit some form of overfill prevention capability at every installation.

Okay, so I think I need to install an Overfill Prevention System... which device(s) do you recommend?

We don’t recommend any specific device(s), since the ideal system will always be installation specific. Instead, we recommend taking guidance from a suitably qualified Storage Tank Technician e.g. a Technician registered with The Oil Firing Technical Association (OFTEC). To find a local Technician, click here to visit the OFTEC website.

Queries? Questions?

If you have any queries or questions on overfill prevention systems, you’re very welcome to contact our Customer Support Team. As a leading supplier of Fuel Oil Tanks to customers across the UK, Republic of Ireland, Channel Islands and Isle of Man, we can help you find the ideal tank and the ideal overfill prevention system to go with it. You can call our Customer Support Team on 01789 632 151 from the UK, Channel Islands and Isle of Man, or 01 5268 642 from the Republic of Ireland. Alternatively, you can email hello@fueltank.store. We’re open from 9am to 5pm weekdays - excluding Bank and Public Holidays. 

Photograph of Carbery, Diamond and Harlequin Oil Tanks on an orange background