Standards for Static Protective FIBC

The ISO Technical Committee TC122 has responsibility for standardization in the field of packaging with regard to terminology and definitions, packaging dimensions, performance requirements and tests.  The Technical Committee is divided into a number of Working Groups (WG) each with responsibility for a different type of packaging or aspect of standardization. There is also a Sub-Committee (SC) of TC122 that has responsibility for standardizing performance requirements and tests for means of packaging, packages and unit loads, TC122/SC3. The standards developed by TC122/SC3 include the series covering transport packaging for dangerous goods (ISO 16101, ISO 16103, ISO 16106 and ISO 16883) and FIBC for non-dangerous goods (ISO 21898). Like its parent committee, TC122/SC3 is also divided into Working Groups, one of which (WG9) is responsible for the electrostatic properties of FIBC. In fact, WG9 is an integral part of a Joint Working Group (JWG) established by ISO and IEC.

The IEC Electrotechnical Technical Committee TC101 has responsibility for standardization in the field of electrostatics, and in particular for test methods to evaluate the generation, retention and dissipation of electrostatic charges, and to ascertaining the effect of electrostatic discharges and other electrostatic phenomena. TC101 is divided into Working Groups and Project Teams (PT) each with responsibility for different product groups or electrostatic phenomena. WG7 was established to develop an International Standard covering:

  • the evaluation of the electrostatic properties of all types of FIBC that are intended to be used for combustible dusts and/or in flammable or explosive environments;
  • a definition of types of FIBC in relation to their construction and intended use;
  • specification of electrical test methods and requirements.

As the scope of IEC TC101 only allows it to develop standard test methods and means of evaluation, a formal liaison is required with ISO TC122, which has the authority to develop standard performance requirements and classifications for the product groups it covers. The liaison takes the form of a Joint Working Group (JWG7). IEC is the lead organization and so JWG7 is convened under IEC TC101. WG9 of ISO TC122/SC3 is in fact a virtual committee that never actually meets. However, members of WG9 nominated by ISO Members do actively participate in JWG7 meetings.

The first standard developed by JWG7 was published in October 2005 as a joint logo standard, i.e. IEC/ISO 61340-4-4.

Outline Structure of IEC/ISO 61340-4-4: 2005

  • Requirements for labelling FIBC that claim compliance with the standard;
  • Performance requirements:
    • Properties required to avoid propagating brush discharges ( Type B, Type C & Type D);
    • Properties required for FIBC intended to be earthed (Type C);
    • Properties required for FIBC not intended to be earthed (Type D);
  • Test methods:
    • Breakdown voltage (Type B, Type C & Type D);
    • Ignition tests (Type D);
    • Resistance to ground (Type C);
  • Information to be included in a test report.

The ignition test is based on procedures developed and used over many years by independent test authorities such as BTTG, Chilworth Technology, Swiss Institute for Promotion of Safety & Security, and by industry leader Texene, LLC. The procedures simulate the actual conditions in which FIBC are used. Electrostatic charge is generated when powders, granules or pellets are loaded into or emptied from FIBC. For any FIBC to be considered safe, it must be demonstrated that under such charging conditions no incendiary discharges are produced from the FIBC itself. The purpose of standardizing the test procedure is to ensure universal application of the correct test conditions. The charging current established by JWG7 and incorporated in to the standard is 3 µA. The flammable atmosphere specified in the standard simulates methanol (the most easily ignitable solvent likely to be present when FIBC are used) with a minimum ignition energy of 0.14 mJ.

IEC/ISO 61340-4-4 was published as a full International Standard in October 2005.

The test procedures specified in IEC/ISO 61340-4-4 are intended principally for type qualification purposes, to demonstrate that a particular design of FIBC constructed from specified materials is safe for use in the presence of a flammable or explosive atmospheres. Other test methods may be more appropriate for routine quality control testing.

In Europe, CENELEC has recently published a Code of Practice for the avoidance of hazards due to static electricity (CLC/TR 50404:2003). The origins of this document are two old established codes from United Kingdom and Germany, BS 5958 and ZH 1/200. The two codes were originally combined in a guidance document published as a CENELEC report R044-001 in 1999. Since then CENELEC Technical Committee CLC/TC44X has worked to update and improve the document with contributions from experts representing National Committees throughout Europe. CLC/TR 50404 has now been sent to IEC for development as an International Standard.

CLC/TR 50404 covers most industrial processes that involve handling solids, powders, liquids, sprays, gases, vapours and explosives. It has one section dedicated to FIBC. For the first time in any standard, FIBC are described using the classification of types that has been used in industry for many years. In recognition of the safety record established by CROHMIQ blue™ static protective FIBC over the last decade, the formal classification adopted by CENELEC experts includes unearthed Type D FIBC and furthermore, CLC/TR 50404 specifies that unearthed Type D FIBC may be used in all areas with equal safety as earthed Type C FIBC as shown in the table below:

Safe Use of Different FIBC Types

Inside FIBC Atmosphere Surrounding FIBC

Non-Flammable Atmosphere Explosive Dust Atmosphere Explosive Gas or Vapour
Non-Flammable
MIE > 1000 mJ
A  B  C  D B  C  D C  D
MIE 3 mJ to 1000 mJ B  C  D B  C  D C  D
MIE < 3 mJ C  D C  D C  D

 

 

Definitions of FIBC Types

FIBC Type A FIBC Type A are made from non-conductive fabric and provide no protection against static electricity.
FIBC Type B FIBC Type B are made from non-conductive fabric. They differ from FIBC Type A in that the breakdown voltage through the fabric, including any coating, shall be low enough to prevent propagating brush discharges.

Spark discharges may occur from the surface of FIBC Type B if they become contaminated or coated with conductive material (e.g. water, grease or oil). Precautions should be taken to avoid such contamination and to avoid conductive objects such as tools or metal clips being placed on the FIBC.

FIBC Type C FIBC Type C are made entirely from conductive fabric or from a non-conductive fabric with interconnected conductive threads or filaments. The pattern of conductive threads or filaments is either:

a grid enclosing an area of non-conductive fabric no greater than 25 cm2,

or a 20 mm stripe, in which case each thread or filament must be interconnected at two separate places (usually at both ends).

FIBC Type C must be provided with a grounding point to which all conductive panels, threads or filaments are electrically bonded. The resistance to the grounding point from anywhere on a conductive fabric and from conductive threads or filaments must be less than 108 ohm (updated to less than 10ohm in the second edition of IEC 61340-4-4 - see below).

The lift loops of FIBC Type C must also contain conductive threads or filaments with a resistance to the grounding point of less than 108 ohm (updated to less than 10ohm in the second edition of IEC 61340-4-4 - see below).

FIBC Type C must also meet the breakdown voltage requirements of FIBC Type B.

In order to prevent spark discharges that might ignite a flammable or explosive atmosphere, it is essential that FIBC Type C are always securely grounded. A label should be attached to the FIBC indicating the position of the grounding point(s) and clearly stating the requirement for grounding. Ungrounded people may become charged through normal activity and could then discharge to ground when touching Type C FIBC. It is essential to follow normal safe practice and ensure that all conductors, including people, are grounded in the presence of flammable or explosive atmospheres.

FIBC Type D FIBC Type D are made from fabric that allows charge to be dissipated without being connected to ground. FIBC Type D fabrics usually contain conductive threads or filaments that dissipate charge safely into the atmosphere by low energy corona discharges. Some FIBC Type D have low resistivity coating that may reduce the risk of incendiary discharges.

Grounding of FIBC Type D is not required.

To be qualified as safe for use in the presence of flammable or explosive atmospheres it must be first demonstrated that FIBC Type D do not produce incendiary discharges under realistic conditions.

Note: The conditions and procedures of test used to demonstrate the absence of incendiary discharges are specified in the draft IEC 61340-4-4.

FIBC Type D must also meet the breakdown voltage requirements of FIBC Type B.

Ungrounded conductors such a metal drums or people may become charged when positioned close to some FIBC Type D. It is essential to follow normal safe practice and ensure that all conductors are grounded in the presence of flammable or explosive atmospheres.

Spark discharges may occur from the surface of FIBC Type D if they become contaminated or coated with conductive material (e.g. water, grease or oil). Precautions should be taken to avoid such contamination and to avoid conductive objects such as tools or metal clips being placed on the FIBC.

IEC 61340-4-4 Ed. 2.0

The second edition of IEC 61340-4-4 was published in January 2012. The main changes with respect to the first edition are:

a)   Adoption of a type classification system for FIBC based on four types: A, B, C and D.

b)   Guidance for safe use of FIBC in relation to hazardous areas and hazardous zones defined in IEC 60079-10-1 and IEC 60079-10-2 is added (similar to the guidance given in CLC/TR 50404 - see above).

c)   Resistance to groudable points limit for Type C FIBC is reduced from 108 ohm to 107 ohm.

d)   Resistance to groundable points and electrical breakdown voltage measurements on FIBC shall be measured at low humidity only.

e)   Requirements for labelling FIBC are changed to improve clarity and ease of recognition by end users.

·      Only official classification, i.e. Type A, Type B, Type C or Type D, can be used on FIBC labels.

·      Labelling as D+, Dplus, CD, etc. is not permitted.  

f)   Classification, performance requirements and guidance for safe use of inner liners in combination with FIBC are added.

g)   An informative annex giving guidance on test methods for quality control and inspection testing is added. 

TEXENE LLC, Textile Technologies of the 21st Century
Textile Technologies of the 21st Century


TEXENE LLC is a leading manufacturer of technical textiles focused on delivering precision engineered, safety performance products worldwide.

ARTICLES ON ELECTROSTATICS

STATIC HAZARDS USING FLEXIBLE INTERMEDIATE BULK CONTAINERS FOR POWDER HANDLING
In the early 1990's, Dr Laurence G. Britton, a highly respected process safety engineer with Union Carbide Corp. (later Dow Corp.), conducted a study of fire and explosion incidents that occurred when FIBC were ...

DANGERS OF COMBUSTIBLE DUST EXPLOSIONS, OSHA REGULATIONS, AND ANTISTATIC FIBC
Following three fatal dust explosions in 2003 alone, the US Chemical Safety &amp; Hazard Investigation Board (CSB) launched a wide ranging study of industrial dust explosions.  This first issue of our Electrostatic Safety ...

CHOOSING SAFE STATIC CONTROL FIBC
The second issue of our Electrostatic Safety Review outlines the development of conductive Type C FIBC and the later development of CROHMIQ, the world's first truly effective Type D FIBC fabric, which provides ...

TESTING & CERTIFYING THE SAFETY OF STATIC PROTECTIVE FIBC
The third issue in our series of Electrostatic Safety Reviews describes the rigorous testing that is demanded by national and international standards such (IEC, CENELEC, NFPA, etc.) in order to prove the safety of ...

NEW DEVELOPMENTS IN SAFETY STANDARDS FOR STATIC PROTECTIVE FIBC
Companies that handle combustible powders in bulk bags, or empty products from bulk bags in environments where flammable solvents may be present rely on safe antistatic FIBC to prevent fires and explosions. Proving safety ...

CHEMICAL ACCIDENTS IN THE NEWS