Anti-Static Bulk Bags: Type C vs Type D and When to Use Each

Type C vs Type D Bulk Bags at a Glance

And this comparison is really just one small part. Your bag’s safety label, test certification and site-specific risk assessment should always come first.

Why Static Builds Up in an FIBC

An FIBC is usually made from woven polypropylene. When you fill or empty it, particles constantly touch and separate from the liner and your bag fabric. This can transfer electrical charge and let it build up.

Different kinds of electrostatic discharge can then happen. Brush discharges might ignite some flammable gases and vapours, propagating brush discharges could ignite combustible dust clouds. And a conductive object that’s charged but not earthed could also release a spark.

So before choosing your bag, make sure you know:

• whether your product’s combustible or flammable
• your product’s ‘minimum ignition energy’ (MIE)
• whether combustible dust could form when you fill or discharge
• whether flammable gases, vapours or solvents might be around your bag
• the hazardous-area classification and electrostatic properties of your task
• whether your operating steps can be followed reliably

Our guide to controlling electrostatic risks when using bulk bags for fine powders will talk you through all of these hazards.

What Is a Type C Bulk Bag?

A Type C FIBC is also called a conductive or groundable bulk bag. Its polypropylene fabric is made of connected conductive threads or tapes that carry electrostatic charge to a set earthing point.

For this protection to work, your bag needs to be securely connected to a verified earth before you start filling or discharging – and it must stay connected. Under the current IEC standard, a Type C bag has a resistance to its groundable point of less than 1 x 10^8 ohms (or 100 megohms).

When you specify and earth it the right way, you can use a Type C FIBCs for your flammable powders and in areas where you’ve got flammable gases or vapours. You can check your route to earth and, if needed, monitor or interlock it with your equipment.

When Should You Use a Type C FIBC?

Type C is your best choice when:

• your site already has a verified electrostatic earthing system
• your operators can connect the right earthing point before every transfer
• the connection can stay secure and, ideally, monitored throughout
• your risk assessment means you need a controlled conductive path to earth
• your bag and any liner have been qualified together for your material and atmosphere

An unearthed Type C bag won’t give you the right protection, and could create a spark hazard. If an earth cable detaches after you’ve started transferring, stop and follow your manufacturer’s and site’s safety steps. Don’t just reconnect your clamp when there’s a chance you might still have charge on your bag.

What Is a Type D Bulk Bag?

A Type D FIBC uses specially designed static-dissipative fabric. Instead of carrying charge through a grid to an earth point, it cuts your hazardous charge build-up and dissipates it through controlled low-energy corona discharges. This means that your bag doesn’t need a direct earth connection.

Using a Type D means you don’t need to worry about forgetting to connect your bag, attaching the clamp the wrong way or losing connection while you’re transferring. This can be really useful for your mobile or multi-site handling and where you can’t guarantee reliable earthing.

When it’s properly tested, labelled and used within its limits, a Type D FIBC could be used for your flammable powders and for areas where you’ve got flammable gases or vapours.

When Should You Use a Type D FIBC?

Type D might be your better option when:

• directly earthing all your bags would be difficult
• your filling or discharge point is mobile or changes a lot
• lots of your operators or sites use the same packaging spec
• you want to rely less on a manual bag-earthing step
• your complete bag design, including its liner, has been tested for your task

It’s really important to remember that “no bag earthing required” doesn’t mean “no electrostatic controls required”. Your conductive plant, tools and other objects still need to be bonded or earthed, based on your risk assessment. Your team might also need anti-static clothing, footwear and flooring. Make sure you follow your bag label and your site’s set up.

Never use your Type D bags for anything they’re not certified for. Heavy contamination or a coating of conductive material, like water or grease, can affect how protective they are. And it’s key that you don’t use your Type D bag as Type C – or as a hybrid “C/D” bag – the recognised classifications are C or D.

Which Is Safer: Type C or Type D?

Neither is safer all round. Type C gives you a measurable route to earth but loses its protection if your earthing fails. Type D takes away your direct bag-earthing step – but isn’t a shortcut around wider electrostatic controls. How reliable your bag is still depends on certified construction, a compatible liner, clean fabric and the right handling.

To make the right choice for you:

• Characterise your product. Confirm combustibility, MIE and electrostatic properties (using reliable test data).
• Assess your atmosphere. Identify any dust clouds, gases, vapours or solvents you might have when you fill, store and discharge.
• Review your process. Think about transfer rate, equipment, operators, earthing points and the possibility of contamination.
• Specify your entire FIBC. Include your fabric, dimensions, filling and discharge design, liner, labels and certification. Don’t pick your outer bag by itself.
• Check your bag’s use. For Type C, confirm how your earth connection will be made and monitored. For Type D, make sure that your surrounding conductive objects – and team – are managed the right way.

If you’re working with materials with very low ignition energies or in unusual conditions, they’ll need to be assessed by a specialist. A generic comparison table won’t give you what you need – make sure you get the right testing and safety advice.

Do Liners Affect the Choice Between Type C and Type D?

Absolutely. A liner changes the electrostatic behaviour of your whole package, so don’t just choose it for moisture, hygiene or barrier performance.

IEC 61340-4-4 classifies static-protective liners as L1, L2 and L3, with an extra L1C construction – and it’s worth remembering that not every liner’s allowed in every kind of FIBC. So a conductive liner used with your Type C bag must be bonded the right way into your bag’s earthing system. And with Type D, your bag-and-liner combination might need ignition testing.

It’s really important to know that adding an “anti-static” liner doesn’t automatically upgrade a standard bag, or make an unapproved combination safe. Ask your supplier to confirm that the complete design is right – and tested – for your task.

Standards, Labels and UK Workplace Responsibilities

IEC 61340-4-4:2018 is the international standard for electrostatic classification, testing, labelling and safe use of FIBCs intended for hazardous explosive atmospheres. In the UK, it’s: BS EN IEC 61340-4-4:2018.

Every one of your static-protective bags should be labelled with its type, uses and instructions. Check your label – don’t just go by colour or appearance.

If you’re a UK employer, you also need to assess and control your fire and explosion risks under the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) 2002. Choosing the right FIBC is a key part of that, as well as controlling your ignition sources, maintaining your equipment, training your team and documenting your safety steps.

Common Mistakes to Avoid

• Using your Type C bag before you’ve got a secure earth connection
• Assuming your Type D bag means you don’t need to earth conductive equipment or manage your team
• Reconnecting your detached Type C earth clamp while filling or discharge is still happening
• Fitting an unapproved liner or changing your bag construction
• Treating your Type C and Type D bags as interchangeable because they’re both called anti-static

Talk to Us About Anti-Static Bulk Bags

Finding the right FIBC spec starts with your product and process, not just your bag. As long-standing suppliers of specialist bulk bags and FIBCs, we can help you work through everything from material, hazardous atmosphere, filling and discharge method to liner, safe working load and certification.

Comparing Type C and Type D? Talk to our expert team to help you make the right choice.