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Why Fusible Caps?

3" Fusible Cap, Polymer Element

Fusible caps are a common item fitted to containers globally. Having said this, a lot of people including those in tank repair depots often ask me what a fusible cap is and what is its purpose? Is it a relief valve, it states a flow rate??

Quite simply, it's a solid cap where the centre will detach when it reaches a particular temperature in an emergency fire engulfment situation. But why?

Bulk liquid containers are designed and manufactured to be safe, that's why we obviously have rules, regulations and standards to meet such as ADR, IMDG and DOT etc. Having said this, there's an element of risk in everything we do and accidents do happen from time to time.

In the event of an emergency on a UN31A, UN31B or UN31N IBC container, Chapter 6.5 of the ADR standard states that: "IBCs for liquids shall be capable of releasing a sufficient amount of vapour in the event of fire engulfment to ensure that no rupture of the body will occur", essentially preventing a bleve (boiling liquid expanding vapour explosion). A fusible cap will allow maximum venting to help prevent an explosion. This also in turn means the tank will be likely more controllable by emergency services attending the scene, preventing further damages.

Some tanks will have an open vent / breather, such as static tanks used to store fuels. These tanks however, unlike the those used for transport, are not transported whist containing product and therefore present less risk of spillage as they aren't moved around. ADR chapter 6.5 also says that "IBCs shall be so constructed and closed that none of the contents can escape under normal conditions of carriage including the effect of vibration, or by changes in temperature, humidity or pressure". Hence the need for a fusible cap and guaranteeing full product containment under normal operations.

In addition to the fusible caps a safety valve can be installed to help protect the tank breathe with minor changes in its pressure or vacuum, whilst still fully containing its cargo. More information about these valves can be seen on future Blogs from TankPart Limited at

Our standard range of Girard Equipment Inc. fusible caps can be seen clicking here.

Thanks for reading


Note: All content is of my own personal view and not those expressed by others.

Credit: ADR for the quotations made from Chapter 6.5.

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