Metal Additive Manufacturing enables entire 3D structures to be painstakingly built layer-by-layer. This method of production offers powerful advantages over traditional techniques but carries potential risks. To safeguard both operators and machines, Process Sensing Technologies provides state-of the art SIL rated technology to monitor any hazardous environments created during this process.
Metal powders used in Additive Manufacturing can react explosively when exposed to oxygen. In the case of Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing processes, which rely on lasers for fabrication, these hazardous conditions can pose a risk, resulting in an explosive atmosphere with an ignition source at its core.
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.
The European Union Machinery Directive (2006/42/EC) [1] states machinery should be designed and constructed to avoid the risk of explosion posed by gases, liquids, dust, vapours, and other machine-produced or used substances. To reduce the risk of explosions, machinery must be constructed in a way that contains any potential blast. Additionally, eliminating ignition sources in accordance with ATEX directive (2014/34/EU) [2] and avoiding external hazards (similar to an internal combustion engine).
Preventing explosion risk by controlling inert atmospheres
Additive Manufacturing machines use lasers or other high-energy systems and therefore have the potential to spark explosions without proper safety protocols in place. To keep such dangers under control, inert atmospheres must be created which reduce oxygen levels below a certain threshold known as the limiting oxygen concentration (LOC). This method is essential for guaranteeing hazard prevention during manufacturing processes utilizing these types of energy sources.
ATEX directive (1999/92/EC) [3] also includes inert atmospheres to prevent explosions, where atmospheres are classified into zones depending on when an atmosphere capable of sustaining an explosion is likely to happen:
- 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.
The employer and operator of the equipment hold responsibility for ensuring any area remains at an acceptable level of safety, classifying it in terms either 'safe' or a specific zone.
The role of SIL2-rated Oxygen Analyzers
Oxygen analyzers are essential for safeguarding workplaces and keeping personnel safe. 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.
Oxygen analyzers from Process Sensing Technologies are supplied with solid state ceramic, thermo-paramagnetic or electrochemical oxygen sensors. These highly reliable oxygen analyzers are usually supplied with sample handling panels that are designed for safety critical applications in additive manufacturing processes. Analyzers with a separate control unit and sensor mounted in or very close to the process are also available. The safety concepts employed are intrinsic safety (IS) and explosion-proof (EXd) cases with flame arrestors and breathers for increased safety.
SponCon - 1
SIL-O2 Oxygen Analyzer
The SIL-O2 Oxygen Analyzer is a compact SIL2 rated unit with 3 configurable alarm outputs and push button calibration. It features an analyzer and galvanic isolation barrier in one device. Measurement range: 0 to 25% O2.
SponCon - 1
Microx Oxygen Analyzer
A compact oxygen analyzer with remote sensor and three display module mounting options. The Microx utilizes zirconia or electrochemical technology and measured; 0 to 100ppm, 0 to 1,000ppm, 0 to 25%, 0 to 96% O2.
SponCon - 1
Oxygen Transmitters
Minox i - Intrinsically safe compact O2 transmitter with 0-10ppm (v) to 0-25% measurement range.SenzTx - Compact and robust O2 transmitter with measurement range: 0 to 100ppm up to 0 to 100% O2.
For more information on PST’s range of Hazardous Area and SIL-rated Oxygen Analyzers, click here.
References:
[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)
