The process of conveying combustible dusts requires caution and expertise from start to finish.
Good engineering practice, dust-tight design, regular house cleaning and protection methods such as venting panels, flameless venting systems, chemical suppression systems help keep the conveying process safe and efficient.
There are many steps to consider, but in this blog, we are going to cover the following:
- What are combustible dusts?
- OHSA Regulations for Compatible Dusts
- How can I safely convey highly combustible bulk solids?
What are combustible dusts?
According to OSHA, NEP combustible dust is defined as particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape. However, NFPA standards and OSHA also indicated that combustible dust less than 40 mesh (425 microns) pose more hazardous.
A dust explosion can be catastrophic and cause employee deaths, injuries, and destruction of entire buildings.
That’s why the dry bulk material conveying solutions from Pneu-Con are designed to prevent any combustible dust explosions.
Across many industries, the manufacturing, processing, transportation, or storage of combustible materials can result in the formation of gases, vapors or combustible dust. Unfortunately, this can form an explosive atmosphere. These include but are not limited to:
- Food (e.g., candy, sugar, spice, starch, flour, feed)
- Metal Processing (e.g., aluminum, chromium, iron, magnesium, and zinc)
What are the 5 elements of a combustible dust explosion?
The five elements of a combustible dust explosion include oxygen, heat, fuel, dispersion, and confinement.
Knowing these five elements is crucial in preventing them from being present in a conveyor system.
OSHA Regulations for Combustible Dusts
After the Georgia Sugar explosion incident, OSHA released National Emphasis Program Directive NEP and declared that most of the powders dispersed in the air could cause dust explosion risk. The end-users should take prevention + protection measures. Below, you can watch more about the Georgia Sugar explosion incident:
Any product, regardless of particle size, can cause a dust explosion. However, finer particles pose more explosion risk.
A fire or explosion with victims is not acceptable for the operator, nor within the frame of the OSHA NEP DIRECTIVE NUMBER: CPL 03-00-008 dated 03-11-08 and NFPA Guidelines.
On top of that, an incident may jeopardize the production contingency, which of course, also is not acceptable.
This directive has the following demands:
A risk analysis (or Dust Hazard Analysis) must confirm that the residual explosion risk is acceptable: the protection measures to be taken should conform with the available knowledge and technology.
The product dust explosion characteristics are generally denoted by the following.
- Kst: Rate of Pressure rise in the event of an explosion, Bar/m-sec
- Pmax: Maximum explosion pressure, Bar
- MIE: Minimum Ignition Energy required to cause ignition (MJ)
Products are also classified in Classes ST0: Kst (0-200) ST1(Kst(200-400) St2 (Kst>400)
Generally, food powders are St0, and metal powder are ST1 or St2
Note: SC Vacuum Systems generally have filter receiver volume of less than 8 Cuft. Hence, they can be excluded from the requirement of explosion protection as per NFPA 652 and other industry-specific combustible dust standards.
Of the many benefits when dealing directly with Pneu-Con is our systems predominantly employ vacuum conveying with low risk. The applied vacuum will result in reduced oxygen content and hence less likely to initiate an explosion. At Pneu-Con, we have spent over four decades aggregating a vast amount of dry bulk material knowledge and pneumatic conveying system engineering expertise.
As the preferred one-stop resource chosen by some of the best-known companies in the world to design and engineer pneumatic conveying systems for food, grain, coffee, chemical, pharmaceutical, nutritional, dairy and plastics applications, we have developed the unique ability to solve almost any dry bulk material conveying issue and design.
Our pneumatic conveying systems are built to prevent combustible dust explosions. Learn more about our vacuum systems here.