Electrostatic testing of a rigid intermediate bulk container (RIBC) intended for use in explosive atmospheres

Rigid intermediate bulk containers (RIBC) of 1 m3 volume, consisting of an HDPE body almost entirely surrounded by metal sheeting, are readily available commercially and are used across a wide range of industries with both flammable and non-flammable liquids. Regarding their use with flammables, these containers have been claimed to be suitable for use in Zones 1 and 2 (IIA and IIB) according to CENELEC R044-001. A draft of IEC 61340-4-6 also implies that this style of RIBC is acceptable for use with flammable liquids with regard to electrostatic ignition hazards. However, testing of one such RIBC showed that discharges of several hundred nanocoulombs could be obtained from the interior plastic surface even when the metal frame was earthed, and also from the cap and around the top opening. In subsequent tests, these discharges were shown to be capable of igniting typical flammable atmospheres. Therefore, it is important to recognize that such containers are not inherently safe with regard to electrostatic ignition hazards, and that additional precautions may be required in order for them to be used safety with potentially explosive atmospheres.