How to Control Inert Environments in Metal Additive Manufacturing using SIL-Capable Oxygen Analyzers

Metal Additive Manufacturing is a process of creating three-dimensional objects by adding successive layers of material. It offers significant advantages over traditional manufacturing techniques, but the process can present a risk. In this blog post, we look at how SIL-capable technology to control inert environments is used to ensure the safety of operators and machinery.

Metal powders in Additive Manufacturing, when exposed to oxygen, can react explosively, and present a potentially serious risk to life. For this type of danger to exist, the metal powder must be in an explosive atmosphere with an ignition source, such as the laser at the heart of the Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing process.


What is an explosive atmosphere?

An ‘explosive atmosphere’ is a mixture of air, under atmospheric conditions, and flammable substances in the form of gases, vapours, mists, or dusts, where combustion spreads to the entire unburned combination after ignition has occurred. A 'potentially explosive atmosphere’ is one that could become explosive due to local and operational conditions, which could be part of the process or due to a machine fault.

In the European Union, the Machinery Directive (2006/42/EC) [1] requires machinery to be designed and constructed to avoid any explosion risk posed by gases, liquids, dust, vapours, and other substances produced or used, or by the machinery itself. This can be achieved by either making the machinery sufficiently robust so that any explosion is contained within it, avoiding external hazards (in the same way as an internal combustion engine), or by eliminating ignition sources in accordance with ATEX directive (2014/34/EU) [2].

Controlling inert atmospheres to prevent risk of explosion

Additive Manufacturing machines employing lasers or other high energy systems, have an ignition source intrinsic to the design, as well as the presence of a fuel in the form of the powder. Explosion prevention relies on the principle of an inert atmosphere, ensuring the concentration of oxygen in the atmosphere is reduced below the limiting oxygen concentration (LOC) of the powder used when the ignition source is present.

ATEX directive (1999/92/EC) [3] also covers inert atmospheres to prevent explosions, where atmospheres are classified into zones depending on when an atmosphere capable of sustaining an explosion is expected to occur:

  • Zone 20: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, for long periods, or frequently (more than 1000 hours per year).
  • Zone 21: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur occasionally during normal operation (10 to <1000 hours per year).
  • Zone 22: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is unlikely to occur during normal operation but, if it does, will persist for a short period (<10 hours per year).
  • Safe Area: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is unlikely to occur under any condition for a period that would pose an intolerable risk to the employer/operator of the equipment.

  • Responsibility for deciding whether an area is a particular zone or safe area, and for maintaining the area at that zone or safe area, belongs to the employer and operator of the equipment.

    The role of SIL2-capable Oxygen Analyzers

    Oxygen analyzers are critical in aiding the employer and operator to ensure their zones or safe areas are maintained reliably to achieve at least tolerably safe working conditions. The oxygen analyzers may be used as part of the basic process control system, for control and operation of the inerting system. They can also be used separately, as an independent safety system to monitor the correct functioning of the basic process control system and initiate a suitable response if a fault is detected.

    For more information on PST’s range of SIL-capable Oxygen Analyzers, Click here.


    [1] Directive 2006/42/EC of the European Parliament and of the Council on machinery, and amending Directive 95/16/EC
    [2] Directive 2014/34/EU of the European Parliament and of the Council on the harmonisation of the laws of the Member States relating to equipment and protective systems intended for use in potentially explosive atmospheres.
    [3] Directive 1999/92/EC of the European Parliament and of the Council on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres (15th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC)

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