What You — and Your Toll Processor — Need to Know About Combustibles

Only three fundamental elements are needed for a fire: fuel, oxygen, and an ignition source.

To ensure safe milling that protects people, equipment, and materials while achieving the desired particle reduction, blending, or drying outcome, toll processors need to exclude at least one of those fundamental elements at all times.

They also need to be aware of materials that may require special handling for certain milling, drying, or blending techniques. Combustibles, for example, are materials that can be easily ignited and burned. Explosives combust in a way that rapidly generates heat and a high volume of gases, creating dangerous pressure.

Knowing as much as possible about a material helps toll processors determine the best procedures for handling and processing to minimize risk of fire or explosion.

Risk Factors for Fire

Intrinsic to toll processing are several factors that can lead to a risk of fire or explosion: 

• Combustibility of some materials
• Increased material surface area created by milling
• Application of energy to reduce particle size (can generate heat)
• Contact between machine parts (can cause sparks)
• Potential interaction between materials when blending

In general, the more energy a mill uses to reduce particle size, the greater the fire risk involved. While mechanical milling processes present an obvious risk due to machine parts in contact with one another, no milling method should be considered fireproof. Blending and drying processes can also present challenges.

External heat sources, electrical wiring, and even static electricity could pose a risk. Reduced particle size increases the combustibility of many materials, and in fact, certain self-heating materials can even auto-ignite.

Safety In Numbers?

Having as much information as possible about a potential mill feed material is critical to preventing fire or explosion. Organic dust explosions and fires have caused numerous workplace deaths and injuries, underscoring the potential for catastrophic outcomes without proper planning.

Materials that can be combustible or explosive include:

• Polymers
• Solid organic materials (including grains, sugars, starches, cellulose, etc.)
• Lipids (can also be present alongside starches in grains)
• Minerals (coal, sulphur, etc.)
• Metals (such as aluminum, lithium, magnesium, etc.)

KSt and Pmax are two important measures that characterize the hazard associated with various combustible or explosive materials. KSt estimates the expected rate of pressure rise in an explosion, while Pmax estimates the maximum pressure (i.e., the violence) of the potential explosion. Materials are classified into four St classes; St 0 indicates no risk of explosion as is the case with silica, while aluminum and magnesium are classified St 3, a “very strong explosion.”

Knowledge is Key to Prevention

Among the first questions your toll processor’s team of material scientists and technical experts needs to answer is whether a material is combustible. Because materials can pose a risk not only during processing but also in storage or while being handled or moved, the appropriate safety data sheet (SDS) is a primary source of information, and any knowledge gained through customer experience is also welcome.

This information can help your toll processor determine which risk management resources and fire protection equipment to employ, such as appropriate PPE, special ventilation systems, isolation apparatus, inerting systems, and fire protection equipment. All of that is no small capital investment, and it delivers risk mitigation value that also protects your equipment, processes, people, and materials.

The more transparency about mill feed materials that you can provide to your processors, the more efficiently — and safely — they can mill, blend, and dry your product. So it’s worth spending a little time understanding the basics of toll processing and particle reduction technology. A great place to start is this Particle Technology Glossary. Just click the link below for your own copy!