Classification of static protective FIBC liners

Specifications and requirements for the safe use of inner liners in static protective FIBC were first introduced in the second edition of the International Standard IEC 61340-4-4, published in 2012. Liners are classified as three types referred to as Types L1, L2 and L3.

Type L1 liners are intended for use in Type C FIBC. Either one or both surfaces have resistivity less than 10^8 ohm. In the third edition of IEC 61340-4-4, published in 2018, another configuration for Type L1 liners was added. This is a liner made from a multi-layer laminate in which the internal layer is a conductive material (typically aluminum). Such liners are classified as Type L1C. A critically important requirement to ensure safety when using Type L1 and L1C liners is that the conductive layer must be electrically bonded to the grounding system of the Type C FIBC, which must also be securely connected to ground. The electrical connection between the conductive materials in the bag and the liner must be robust to withstand filling, transport and emptying. If the electrical connection fails for any reason, the liner becomes an isolated conductor, which is extremely dangerous. Isolated conductors are a primary cause of explosions caused by electrostatic discharge.

The Type L2 liner can be considered as the general-purpose static protective liner because it can be safely used in Type B, Type C and Type D FIBC. There are several different permissible configurations of Type L2 liners, which are explained in more details below.

Type L3 liners are only permitted in Type B FIBC. They are made from insulating materials, but must have a breakdown voltage of less than 4 kV to prevent the occurrence of propagating brush discharges.

Permissible configurations of Type L2 liners

Permissible configurations and requirements for Type L2 liners are summarized in the table below.

Permissible configurations of Type L2 liners

A further requirement for Type L2 inner liners when fitted inside Type D FIBC is that the FIBC and liner combination shall pass ignition testing. Texene conducts the necessary testing to qualify specific designs and combinations of CROHMIQ® Type D FIBC and Type L2 liners.

Permissible combinations of static protective FIBC and liners

Provided both FIBC and liner meet the specified safety requirements individually, IEC 61340-4-4 specifies which combinations of FIBC and liner are permissible and which are not permissible, as summarized in the table below.

Permissible combinations of static protective FIBC and liners
Additional safety requirements

One additional safety requirement in IEC 61340-4-4 is that conductive materials, aluminum for example, must not be used in any layer of Type L2 or L3 liners. Using conductive materials in a liner for a bulk bag that is not normally grounded, i.e. Type B and Type D FIBC, creates a risk, because conductive materials must always be grounded to avoid hazardous electrostatic discharge.

Note: laminated aluminum layer liners are often used in food contact and other sensitive applications because they provide an excellent barrier to oxygen and odors. Other designs of laminated liner are available, e.g. polyethylene/nylon/polyethylene, that also have excellent oxygen and odor barrier properties, and are acceptable for use in Type D FIBC provided they meet the requirements for Type L2 liners shown above.

Another safety requirement in IEC 61340-4-4 is that the inclusion of a liner does not change the type classification of FIBC. For example, placing a Type L2 liner in a Type B FIBC does not permit the bag to be used in hazardous areas containing flammable gases or vapors. The bag is still classified as Type B and is subject to the requirements and restrictions for safe use of Type B FIBC.