The risks of pneumatic conveying
It is easy to see why pneumatic conveying has quickly become such a popular solution for transporting bulk goods over relatively short distances. When done right, it is a highly effective, efficient, flexible and reliable method of moving a wide range of materials within a production facility or to and from vehicles.
Like nearly every production process, however, it does involve some risks, especially if subpar equipment is being used and the proper safety precautions have not been taken.
In the case of pneumatic conveying, the main hazard is dust.
Types of dust
There are two types of dust that pose a potential risk :
- Explosive dust is generated when certain materials are conveyed.
- Dust is present in very dusty ambient environments. This not only includes the dust concentration in the air but also dust that has accumulated on the equipment or other surfaces.
First, it is important to note that not every type of dust is problematic. In order to be dangerous, the dust needs to be capable of catching fire and exploding when it is mixed with the oxygen in the air.
What is explosive dust?
As a rule of thumb (although there are exceptions, which you will see below), this explosive dust is a byproduct of industrial processes, including pneumatic conveying, that involve combustible materials.
Unfortunately, there are more combustible materials than one might think. For example, the dust generated when handling many foods and other organic substances, such as sugar, flour, grain or wood, is combustible.
In addition, many chemicals and metals – and even some nonmetallic, inorganic materials – can be sources of explosive dust, which is practically invisible to the human eye. That means that some materials that are not usually considered to be “combustible” in large pieces (such as iron or aluminum) can burn or explode if they are present in the right concentration and if the dust is fine enough.
As a result, any workplace where dust is created or could accumulate is a potential hazard and should be evaluated for the risk it poses. Because explosive dust should not be taken lightly.
The dust explosion pentagon
However, to have a devastating effect, multiple conditions have to be met. This is often also referred to as the dust explosion pentagon.
Any fire needs three elements to burn: Fuel, oxygen and an ignition source. In order to combust, the right concentration of dust also needs to be dispersed (i.e., present in the air), and the resulting dust cloud has to be confined in an enclosed or limited space. All of these five conditions have to be met. That means, for example, that a dust explosion is not possible in an open-air setting or if there is no oxygen or spark.
The dust explosion pentagon also illustrates why some pneumatic conveying systems pose a risk. They are used to transport many of the aforementioned materials, they are enclosed spaces (piping network, silos,...), and the dust can be dispersed.
The dangers of working in a dusty environment
But not only does the dust in a pneumatic conveying system pose a potential risk. There are also inherent dangers of working in a dusty environment, i.e., if the ambient environment in which the system operates is very dusty itself.
In that case, the five elements of the dust explosion pentagon may be present outside of the pneumatic conveying system. And, if the wrong equipment is chosen, the system itself could provide the spark that leads to an explosion.
How to avoid an explosion
Fortunately, the risks of both scenarios can be mitigated with the proper technologies and safeguards. Essentially, all that has to happen is for one of the elements of the dust explosion pentagram to be taken out of the equation.
It is important to understand the risks and to be able to rely on the proper technology. And this is where the ATEX directives of the European Union come into play. They specify the requirements for workplaces and equipment in an explosive environment.
As a first step, you need to look up which the relevant ATEX zone(s) are defined for your site . With this information, you can contact an equipment supplier that can help you get the certified equipment you need. It is extremely important to note that there is no one-size-fits-all solution to mitigating the risk of an explosion. This means an equipment manufacturing company has to look into your specific case in order to build a customized solution that fits the needs of your process.
