Expandable polymeric beads
|Infobox on Expandable polymeric beads|
|Example of Expandable polymeric beads|
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|Risk factors||See text|
Expandable polymeric beads
Polystyrene is formed from styrene through suspension polymerization, a process by which tiny drops of the monomer (in this case, styrene) are completely surrounded by water and a mucilaginous substance. Supporting and surrounding the styrene globules, the suspension agent produces uniform droplets of polystyrene.
Next, a polymerization initiator is added to the droplets, which are suspended by heat radiation of about 100° Celsius. This results in free radicals, a group of atoms particularly likely to react with others because they contain unpaired electrons which are available for molecular bonding. Free radicals then combine at randomly to form chains of polystyrene.
Stopping the polymerization process is difficult. Terminators are introduced to the process to end it at the appropriate time. Though variable, chain length must fall within a certain range, because polystyrene with overly long chains won't melt readily, and polystyrene with short chains will be brittle.
Preparing the beads
After polymerization is complete, the mixture—consisting of beads made up of polystyrene chains—is cooled. These beads are then washed out and dried. Uniform bead size is achieved by sorting the beads through meshes which filter out over- and undersized beads.
Shipment / Storage / Risk factors
Expandable polymeric beads are a moulding material in the form of granules or beads, approximately 3 mm in diameter. The beads or granules may contain between 5% and 8% of a volatile hydrocarbon, chiefly pentane. During the moulding process, the beads are heated causing expansion and fusion, forming the familiar polymeric packaging material. During storage or transport, the material will release a portion of the pentane. The rate of this release is increased with a rise in temperature. The beads have been found to generate flammable concentrations of gas in enclosed spaces, and have been involved in several major explosions – in one incident causing severe damage to a container ship.
Expandable beads are included in the IMO Dangerous Goods Code, under Class 9 (Miscellaneous dangerous substances and articles). Various packaging is recommended in the IMO Code, including outer drums and inner plastic packages. Intermediate bulk containers include composite fibreboard or plastic materials.
Except for transportation by highway and rail, the packaging must be capable of containing any evolving gases from the contents during normal conditions of transport. The IMO Code states that storage and segregation is category ‘A’, on deck or under deck, but mechanical ventilation should be provided for under-deck stowage to prevent the formation of a flammable atmosphere. The Code advises that, during storage, a small proportion of the pentane may be released to the atmosphere and this proportion is increased at elevated temperatures. There is also a cautionary note relating to the opening of the doors if the material is carried in containers.
Reputable manufacturers of polymeric beads are well aware of the hazards of storage and transport of the beads and provide detailed lists of precautions to be observed. They provide detailed warning labels to be fixed to drums and freight containers, labels in several different languages and graphic symbols.
The recommended storage should be in a well-ventilated space and preferably below 20°C. Warehouse storage below 20°C may be a relatively simple operation. However, stowage in the holds of an ocean vessel may not be as simple. Stowage should, at least, be away from heated bunker tanks or engine room bulkheads. Research has indicated that temperatures in ship’s holds might be of the order of 65°C+ in some tropical areas.
Obviously adequate hold ventilation with ‘suitable equipment’ should be stressed because the arcing of an electric fan motor may readily ignite a flammable concentration of pentane in air. Deck temperatures in tropical climates can also exceed the recommended limits for safe stowage of the beads. However, if the cargo is containerised, the containers can be placed in a central area of the stow and thus be insulated from the effects of direct sunlight. This arrangement will obviously create extra movement during loading and discharge, but can nevertheless assist toward safe carriage. Pentane released from containers in deck stowage will be dispersed by wind and movement of the vessel, and should not create flammable or explosive conditions outside the containers. Manufacturers are well aware of the problems of release of pentane into freight containers. Recommended ventilation periods are suggested prior to entry and un-packing the container. The pentane hazard is real, it emphasises that if opened in a container yard, the containers should not be sited near drains, because pentane released when the doors are opened could enter the drains creating a potential fire hazard at some nearby location.
Transport by Road or Rail
In Europe there are regulations for transport of products by road (ADR) and by rail (RID). EPS is classified in RID as Class 9 of the regulations for transport of dangerous goods: “Polymeric beads expandable, evolving flammable vapours”. For domestic movements and journeys covered by ADR it is recommended that closed containers of boxes are avoided.
Transport by Sea
EPS is classified in Class 9 of the IMDG code, where it is noted that the product can evolve flammable gases and that good ventilation must be guaranteed if it is stowed under deck. This is essential to ensure that ignitable concentrations of pentane are not formed within the ship. IMDG requires a cautious approach when entering or opening the doors of a freight container. This regulation was introduced because a number of products may give rise to unsafe concentrations of toxic or flammable vapours or an oxygen depleted atmosphere. The same applies for the transport of EPS in closed box vans.
Some shipping lines may be able to offer ventilated containers for certain destinations. However, it has been found that there are wide variations in the effectiveness of such ventilation and it is advised that such containers are tested. If ventilated containers are used, it is also recommended that particular checks are made with the shipping line with regard to the adequacy of the mechanical ventilation provided on the vessels used on the relevant route. It may also be appropriate to question operating practices during bad weather.
Closed (Non Ventilated) Containers
Closed (Non Ventilated) Containers are provided as a general standard by most shipping lines. These containers are acceptable since any significant concentration of pentane gas should be retained within the container and proper training of people at receiving locations can minimise any risk from potential ignition of pentane vapours.
Specific Recommendations for Transport in Closed Spaces
In all cases where proper ventilation cannot be guaranteed (e. g. in closed containers or closed vans) the measures hereinafter described should be taken to avoid the ignition of the gas mixture.
Stowage of Drums
Friction can generate sparks during transport of loosely stowed metal drums. To prevent this the load should be stowed in such a way that during normal transport operations movement is eliminated as far as possible. Stowage should be such that drums from the upper layer cannot fall down and cause any sparks, either in transit, or when the freight container or closed box doors are opened. Adequate dunnage should also be used to eliminate metal to metal contact.
Load Securing of Octabins
Packages should be secured in such a way that movement in transit is prevented.
Safety Information Required in Shipping Documents
To ensure that all parties who come in contact with EPS are aware of the properties of the product, all suppliers should ensure that shipping documents include a written warning, with appropriate signage, as follows:
- Polymeric beads, expandable, evolving flammable vapours;
- Keep away from sources of ignition:
- No fire or naked lights
- No smoking, no welding
- Do not produce sparks by using tools (e. g. metal hammers)
- No hot surfaces above 250°C
- Stow away from sources of heat
Before unloading, ventilate transport equipment by allowing it to stand for at least one hour with the doors open.
To ensure that all those involved in the physical transport, storage and devanning of freight containers or closed box vans are aware of the potential hazards, all such transport equipment should be adequately labelled. It is important to avoid an ignitable pentane/air mixture coming into contact with an ignition source whenever the doors of such transport equipment are opened.
The recommended minimum ventilation time before devanning is one hour.
The main risks associated with EPS are related to the flammable blowing agent and the combustible nature of the polymeric material. Explosion and/or fire are thus significant risks that must be prevented when storing EPS beads. The pentane blowing agent is liberated very slowly during storage. It is a highly flammable gas and can form explosive mixtures with air at concentrations between 1.4 % and 7.8 % volume. It is also heavier than air and sinks to ground level.
EPS beads are not easily ignited but once ignited burn readily. The major products of combustion are carbon dioxide, carbon monoxide, and soot (dense black smoke). Fire retardant grades can release small amount of hydrogen bromide. EPS beads should always be stored in the original labelled, sealed container. If all beads are not used at once, octabins should be tightly closed (minimise the free space) and marked properly. Note that the inner plastic liner is specially designed for packing of EPS, it is strong and acts as a barrier to pentane loss.Each European country may have legislation on the requirements for storage of Dangerous Goods. These should be checked to ensure compliance. It is good practise to ensure that EPS bead is stored in an environment that protects the product, ensures it is away from sources of ignition, and is stored in a safe environment that has fire extinguishing systems. There are some simple inexpensive precautions that can be taken, to reduce the risk of fire when storing bead.
The main sources of ignition are smoking and electrical sparks. A no smoking policy should be enforced in all warehouse and production facilities. Using a naked flame is obviously the single most dangerous act in a flammable environment. Electrical Equipment should be grounded and checked for state of repair. It is also recommended to check pentane levels with a meter before starting any work. Static electricity should be controlled by earthing. To limit the risk of electrostatic discharge from octabin protective covers, they should be removed before entering the pre-foam area of the factory.
The warehouse used for storing EPS bead should be to separate away from the factory. Additionally, Automatic fire detection systems, which will raise the alarm and activate a fire suppression system such as water sprinklers are considered best practise. Realistically, however, to implement best practice could be prohibitively expensive for many companies. Fortunately there are some simple inexpensive precautions which can be taken, to reduce the risk of fire, in any factory that handles expandable polystyrene and these should be considered as recommended or GOOD practice!
- Throughout the factory there must be adequate fire fighting equipment.
- Extinguishers and fire call points should be strategically placed in the warehouse and at high risk areas.
- All factory personnel should be trained in their use.
- Each company should appoint a responsible person to manage safety – he or she should check that the fire protection equipment works properly.
Ventilation & Isolation From Heat Sources
Octobins should ideally be stored indoors to protect them from environmental conditions such as rain and direct sunlight. However, two precautions are important with indoor storage: adequate floor level ventilation and isolation from sources of direct heat e.g. hot machinery and direct sunlight. This may accelerate the loss of blowing agent. The warehouse is required to have floor level ventilation to prevent the accumulation of blowing agent vapour. Ventilation either by air flow or fans to avoid is recommended. Particular attention should be given to the formation of pockets of pentane in areas below ground level.
EPS beads are small spheres that are hard and mobile. Any product spillage must be cleaned up immediately either with a brush & pan or vacuum to prevent accidents due to slipping. EPS beads must be prevented entering drains and the water system. EPS will sink in fresh water but may float or sink in seawater depending on the salt content.
Personnel Protection Equipment
The use of eye-protection is recommended when handling EPS to prevent small beads entering the eye.
Damage to Octabins
If an octabin is accidentally punctured it should immediately be re-sealed with strong adhesive tape to avoid bead spillage. The product should be handled carefully and repackaged or used immediately.
It is not recommended to stack octabins more than one layer high. But if octabins are stacked in two layers always have a strong plywood sheet between octabins stacked on top of each other. Avoid direct contact with excess moisture as this may weaken the octabin. If there is a risk of moisture contact, the octabins should be protected by a waterproof plastic cover and never be double stacked.
When EPS beads are stored in silos, an inert gas blanket should be applied. Silos should be designed to have strong walls and weak roofs, so that should an explosion occur the destructive forces are directed upwards. All storage silos should be properly earthed. Floor of the storage room should not consist of (or covered by) materials that may accumulate static electricity.
Non-bulk shipments of Polymeric beads (or granules), expandable, evolving flammable vapor and Plastic molding compound in dough, sheet or extruded rope form, evolving flammable vapour must be packed in: wooden, plywood, fiberboard, reconstituted wood boxes, plywood drums or fiber drums with sealed inner plastic liners; in vapor tight metal or plastic drums; or packed in non-specification packagings when transported in dedicated vehicles or freight containers. The packagings must be capable of containing any evolving gases from the contents during normal conditions of transportation.
Bulk shipments of Polymeric beads (or granules), expandable, evolving flammable vapour or Plastic molding compounds in dough, sheet or extruded rope, evolving flammable vapour may be packed in non-specification bulk packagings. Except for transportation by highway and rail, bulk packagings must be capable of containing any gases evolving from the contents during normal conditions of transportation.
Handling and Storage Procedures
Transport/Store only in sealed full containers below 27°C in well-ventilated areas away from all ignition sources. Open in preparation for use only. Allow 10 minutes after opening original container for excess flammable vapour to dissipate before moving to processing area where heat sources exist. When part full containers must be used, blow air across open top for 5 minutes before moving to process area to prevent formation of flammable vapour. Provide good ventilation in use area to prevent flammable vapour accumulation. All equipment must conform to applicable electrical code. Clean up any spills as soon as possible. Beads are extremely slippery on any hard smooth surface/cause serious slipping/falling hazard.
IMDG Code Special Provision Polymeric beads and moulding compounds may be made from polystyrene, poly(methyl methacrylate) or other polymeric material. Polystyrene beads sometimes contain flammable vapours when shipped in sea freight containers. IMDG Code 220.127.116.11.2 states: When, for any reason, it is necessary to open the doors of a cargo transport unit, the nature of the contents and the possibility that leakage may have caused an unsafe concentration of toxic or flammable vapours or have produced an oxygen-enriched or -depleted atmosphere shall be considered. If such a possibility exists, then the interior of the cargo transport unit shall be approached with caution.
Therefore the container MUST BE marked with placard stating: "WARNING, MAY CONTAIN EXPLOSIVE MIXTURES WITH AIR. KEEP IGNITION SOURCES AWAY WHEN OPENING".