The first part of this article in the Type D FIBC Technology Monthly Newsletter for July 2024 explained testing and measurements made by Texene that quantified electrostatic risks in expandable polystyrene (EPS) processing operations. The testing proved that there is a very real potential for explosion when using Type B FIBC in EPS operations.
To further support this safety critical conclusion, in this part we look at the UN regulations and the safety statements published in EPS manufacturers’ safety date sheets (SDS).
UN Regulations
The UN Model Regulations for the Transport of Dangerous Goods assign expandable polystyrene (EPS) to Class 9, with the substance number and description: 2211 POLYMERIC BEADS, EXPANDABLE, evolving flammable vapour. FIBC for packaging EPS are labelled with the UN hazard diamond as shown below.
EPS is assigned to a hazard class because of the flammable gas, most commonly pentane, which is used as a blowing agent in EPS. As with any flammable substance, the main risk is ignition leading to fire or explosion.
Safety Data Sheets
A review of Safety Data Sheets (SDS) for EPS reveals that warnings about the presence of pentane and the fire and explosion hazards it creates are typically included. Below are eleven extracts from some SDS published by leading EPS manufacturers:
In use may form flammable/explosive vapor-air mixture. Product releases pentane, a flammable vapor.
Releases vapors which are flammable when exposed to lit smoking materials (cigarettes), sparks, static electricity discharges or open flame. Supports combustion. Explosion risk. Vapors are flammable and heavier than air. Vapors may travel across the ground and reach remote ignition sources causing a flashback fire danger.
Risk of dust-air explosion is increased if flammable vapors are present.
DANGER EXTREMELY FLAMMABLE VAPOR
WARNING VAPOR MAY CAUSE FLASH FIRE
Danger! Extremely flammable materials may release vapors that travel long distances, ignite, and flash back. Containers may explode in a fire.
Explosive air-vapor mixtures may form. Pentane vapors may be emitted from newly opened containers or when the product is heated. If ignited, there could be a very high rate of flame propagation.
Product is a white bead which releases highly flammable pentane vapors. In use, may form flammable/explosive vapor-air mixture.
Flammable. Releases flammable vapor.
The product is combustible. Vapors may form ignitable mixture with air.
Vapors are heavier than air and may accumulate in low areas and travel a considerable distance up to the source of ignition. Because of danger of explosion, avoid vapors reaching the cellar, sewage water and pits. Empty containers may contain flammable residue.
As with any flammable substance, it is imperative that all potential ignition sources are eliminated. The major ignition source that is relevant to packaging is electrostatic discharge. Some SDS warn about electrostatic charging of EPS, and most SDS warn about the need to avoid electrostatic discharge. A further fourteen SDS extracts are shown below.
Electrostatic charge may be generated during manipulation with the product.
Take action to prevent static discharges.
Keep away from heat, hot surfaces, sparks, open flames and other ignition sources.
Electrostatic discharge can be a source of ignition due to accumulated pentane vapors exceeding the L.E.L. (lower explosive limit) of 1.5% (15,000 ppm).
Take precautionary measures against static discharge.
Static electricity and formation of sparks must be prevented.
This material can accumulate static charge which may cause spark and become an ignition source.
The substance/product in bead or expanded form generates static charges during handling which are difficult to dissipate due to the insulating properties. Take precautionary measures against static discharges. Containers should be opened carefully in well-ventilated areas to avoid static discharge.
Substance/product is capable of accumulating a static charge which could act as an ignition source.
Higher line velocity can increase the build-up of static electric charge.
Maintain relative humidity at 40% to minimize static accumulation.
Avoid all sources of ignition: heat, sparks, open flame. Avoid electro-static discharge.
Product may charge electrostatically.
Prevent electrostatic charge – sources of ignition should be kept well clear.
When packaging EPS in bulk bags, hazardous electrostatic discharge can be prevented by using the correct type of static protective FIBC. National and International standards specify the classification of static protective FIBC and the hazardous areas in which they can be safely used.
National & International Standards
The requirements for the safe use of FIBC in potentially explosive atmospheres are specified in National and International Standards, including NFPA 77: 2024 and IEC 61340-4-4: 2018 (see Type D FIBC Technology Monthly Newsletter for March 2024).
The handling of pentane within EPS operations involving FIBC will create Class I Division 1 or Division 2 hazardous areas (NFPA terminology). In IEC terminology pentane is classified as Explosion Group IIB. The minimum ignition energy (MIE) of pentane is 0.22 mJ [1] . The handling of pentane within EPS operations involving FIBC will create Zone 1 or Zone 2 (gas zones) hazardous areas.
It is clear from both NFPA 77: 2024, Table 16.6.3 and IEC 61340-4-4:2018 Table 5, that either Type C or Type D FIBC are required when handling pentane. Furthermore, in NFPA 77: 2024 § 16.6.4.2 (2) and 16.6.5.4 (3), it is explicitly stated that Type A and Type B FIBC should never be used in areas where a flammable gas or vapor is present.
National and International Standards prohibit the use of Type B FIBC for operations in which pentane is present.
It should be noted that safe use of Type C FIBC in hazardous areas is contingent on the bag being properly grounded. Failure to ground the bag because of operator error, or other reasons, renders a Type C FIBC extremely dangerous.
IEC 61340-4-4: 2018 requires that FIBC tested and qualified as Type B, C and D shall be labelled. The labelling for Type B FIBC clearly identifies that it can only be safely used in hazardous areas containing combustible dust atmospheres where the MIE is greater than 3 mJ. The IEC requirements for safety labels for static protective FIBC were covered in the Type D FIBC Technology Monthly newsletter for July 2024.
Conclusion
To take account of the warnings, and comply with the safety instructions in EPS Safety Data Sheets, it is necessary to use the correct static protective FIBC that are qualified in accordance with recognized standards. CROHMIQ bags are tested to and fully comply with the essential safety requirements specified in IEC 61340-4-4: 2018 and NFPA 77: 2024 for Type D FIBC.
CROHMIQ Static Protective Type D FIBC are the safe bulk bags for all EPS operations.
Follow this link to read more about the CROHMIQ Safety Advantage.
______________________________________________________________________
[1] Haase, H. (1977) Electrostatic Hazards, Their Evaluation and Control, Verlag, Chemie, Weinheim.