Metal powder production: OHS risks first!

To be a successful metal powder producer, you must first know your product and the desired production volume. Metal powders are often highly reactive and can also sometimes be flammable, carcinogenic and, under certain conditions, explosive. It is therefore necessary to be familiar with the Standard for Combustible Metals - NFPA 484 and the Occupational Safety and Health Administration’s Combustible Dust National Emphasis Program (U.S. Department of Labor). The necessary information to design production lines and other infrastructures can also be obtained from companies that specialize in metal powder characterization.

In short, when designing the best facilities without compromising operational efficiency or worker health and safety, it is essential to be familiar with both the environmental context and the properties of metal powders and their derivatives.

The risks

Metal powder production generally involves five stages. In Figure 1 below, those with the most risk are shown in red, and those with lesser risk in orange to yellow. Each stage has different risks that must be properly identified in order to mitigate them and minimize any operational impacts. Contingency plans must always be prepared, even in cases where the severity or probability of a risk is significantly reduced.

Stage 1: Producing raw metal powder

When raw metal powder is produced by means of atomization, evaporation, hydrometallurgy or plasma , the associated risks are mainly due to suffocation hazards, light glare, those inherent in the handling and manufacture of hazardous products, and the presence of electricity and/or heat. To address this set of risks, the design of safe and effective production and maintenance activities must be insightful and thorough. For example, these risks can be mitigated by the installation of electrical interlocks, gas detectors and light filters. Another extremely effective mitigation procedure is to integrate an inerting and shutdown (zero energy) sequence before either starting up equipment that contains raw powders or exposing the equipment to the atmosphere, provided that the proper execution of this procedure can be checked. The overall challenge in metal powder production lies in the wide range of risks involved. That is why considerable ingenuity is required to manage the risks associated with combustible dust in environments that combine heat and electricity.

Stage 2: Separation/classification

The risks involved in separating and classifying raw metal powders are mainly associated with the generation of dust clouds and the handling of fine particles. As fine particles are more reactive, they need to be handled with greater care. Risks can be mitigated by reducing the size of the containers for collecting fine powder and installing instrumentation to maintain an inert environment during handling. Since dust clouds can be a source of deflagration, the installation of dust detectors that can shut down the ventilation system so that the dust settles is an interesting mitigation strategy. The likelihood and consequences of dust cloud deflagration in the separation/classification area must be thoroughly and accurately assessed to determine whether the production environment should be electrically classified and designed accordingly.

We'll be discussing the reactivity associated with powder size in more detail in a separate article.

Stage 3: Homogenization

Homogenization consists of combining a set of powders to obtain a homogeneous mixture. The risk in homogenization mainly relates to the large quantity of swirling powders that contain high potential energy in the event of deflagration. Here again, the control of the atmosphere within the homogenization equipment and the electrical classification of the production environment must be assessed and then designed accordingly.

Stage 4: Conditioning

At this stage, large volumes of powder are handled and divided into smaller quantities in containers for transportation from one area to another without requiring special protection. The choice of these containers, including their size, is dictated by the properties of the powder concerned, transportation standards, and customer needs. The risks associated with this stage are related to the movement of large quantities of powder and the generation of dust clouds as the containers are filled. The mitigation approach is always the same, namely, the potential classification of the production area in order to control the atmosphere inside the equipment.

Stage 5: Packaging

At the packaging stage, the powder containers are prepared for shipment, where the risk is associated with handling containers of hazardous materials. At this stage, the powder is protected and can escape only if the containers are damaged. Mitigation of this risk requires an ergonomic layout of the work area in order to minimize handling errors.

Conclusion

Metal powder production involves many risks, some fatal, that need to be mitigated. In this context, investment costs are directly related to the number of mitigation procedures to be implemented and how these are carried out. There are numerous commercially available solutions to mitigate the effects of deflagration. To optimize use of post-deflagration solutions without compromising safety and thereby mitigate pre-deflagration risks, ingenious yet affordable solutions are the obvious choice. This can be achieved by grouping similar hazards, reducing the number of material handling operations, and implementing an evacuation system that detects and responds appropriately to any hazardous situation. Adoption of these solutions requires input from engineers and other experts to achieve an optimally balanced ratio of cost vs. operational efficiency vs. safety. For any project related to metal powder production, do not hesitate contact BBA.