Two potential hazards that can arise during bulk bag handling:
- Explosion: During filling or discharging some bulk solids can generate enough static charge to ignite flammable vapors, gases or dust. Also, various bulk solids, if allowed to accumulate in a high enough concentration, may explode if exposed to an ignition source.
- Health hazard. Bulk solids that present a health hazard to humans via direct contact.
There are two ways to mitigate the risk of static discharge: bag and equipment design.
Of the four types of bulk bag (Type A, B, C and D), typically only types C and D are used to prevent static discharge leading to explosions.
Type C bulk bags feature conductive fabric or conductive threads/filaments woven into non-conductive fabric. The key factor is that Type C bags must have a grounding point to which all fabric, threads or filaments are connected. The grounding point must then be connected to an external ground point during filling and discharging of the bulk bag.
Type D bulk bags are constructed from fabric that allows static charge to be dissipated without being connected to ground. The advantage of Type D bags is that operators are not required to making a ground connection with the bag prior to filling and unloading – a task that can be easily forgotten resulting in disaster.
Equipment used in situations where static discharge could ignite flammable substances must, as a minimum, have ground lugs. Depending on the Area Classification electrical components may have to be intrinsically safe and/or explosion rated.
If the product being filled or discharged can cause an explosion if a high enough concentration of dust is exposed to an ignition source, dust containment is critical.
Bulk bag fillers must have ‘twin-tube’ fill heads and provide a tight seal with the bulk bag inlet spout. The outer tube of the fill head must then be connected to an appropriately designed dust collection system so that dust laden air that is displaced during the filling process is safely extracted.
Bulk bag dischargers must have dust containment features suitable for the hazard level. There are different levels of dust containment available.
All equipment must feature electric components rated for the Area Classification.
Isolate Human Contact
Bulk solids that are health hazards include various refined metals that are carcinogens, chemical compounds that cause respiratory problems and so on. When dealing with these products maximum dust containment is required.
Specialized bulk bag discharging equipment is available for this application. It is critical that such equipment contain dust at the following critical steps in the bulk bag unloading process:
- Initial onset of product discharge. The point in time when product begins to flow from the bulk bag can create a large amount of dust.
- Throughout bulk bag emptying. Of course, dust must be contained as the bulk bag is emptying.
- End of discharge. Near the end of the discharge cycle the bulk bag will lose its shape. Equipment must be designed to maintain dust containment integrity at this crucial stage.
- Bag removal. Removing the empty bulk bag – still full of dust laden air – must be done safely without exposing operators to dust.
Further, bulk bags must be designed to prevent the escape of product particles during handling – otherwise referred to as ‘sifting’. Coated or lined bags can be specifically designed to suit the product and the hazard.
This is only a brief overview of handling hazardous goods in bulk bags. Any potentially hazardous bulk bag handling application must be carefully assessed relative to Standard Operating Procedures, standards and regulations, Area Classification and other factors. Bulk bag and bulk bag handling equipment manufacturers must also coordinate closely to ensure safety.