Since nanotechnology is used to produce a wide range of products and solutions, many workers can be exposed to nanomaterials at work. Nanomaterials are often produced in closed systems, but exposure can also take place during maintenance work or during the handling of finished products.
Legislative guidelines are therefore of the utmost importance. The European Union is pushing the development of new technical standards for nano-materials. This concerns standards that can also be used for characterizing the exposure to nanomaterials in the workplace. The European Commission has issued a specific directive to develop new standards related to nanomaterials in the workplace. Several technical committees are working on this mandate, including CEN.
The Comité Européen de Normalisation, also known as the European Committee for Standardization, introduced the NEN-EN 17199-4:2019 in February of 2019. Essentially the document offers a guideline for Measurement of dustiness of bulk materials that contain or release respirable NOAA or other respirable particles in relation to workplace exposure; Part 4 specifically focusses on the small rotating drum methodology.
What are NOAA
NOAA stands for (engineered) nano-objects and their aggregates and agglomerates. But what are these NOAA? NOAA have found a wide array of applications in many different production processes and industries. NOAA can generally be viewed as structures on a scale comparable with viruses, molecules or in some cases even atoms and can be found in industrial processes such as silver nanoparticle synthesis, production of thin nanocarbon layers, 3D-printing based on a nanohydroxyapatite-polymer composite and so on.
Health risks and NOAA
Apart from its many advantages, the use of engineered nanomaterials can also threaten human well-being, primarily because of their potential toxicity.
While human exposure to NOAA may in theory happen during any stage of the material lifecycle, it is most likely to occur in the workplace where these materials are produced or handled in either large quantities or over long periods of time. Because of its small size, diameters in the lower nm range, the material is easily absorbed either through the skin or through inhalation.
The respiratory system is one of the primary methods of exposure in the work place. The inhaled nanomaterials, because of their very small size, can reach the bloodstream, passing through membranes and accumulate in the organs which may lead to the compound crossing of the blood-brain barrier. These nanometer NOAA compounds can be internalized by cells and affect basic cellular activities such as metabolism, proliferation and differentiation.
Challenges when measuring Nano-dust
The problem that arises when measuring nanoparticles is that many instruments are non-specific. The measured results don’t distinguish between the engineered nanoparticles from environmental nano-sized particles. For this a three-tiered approach was written based upon a systematic evaluation of previously proposed and used strategies and assessments. The EN 17199-4 has a different approach to this.
What does the EN 17199-4 specifically refer to?
This standard sets out to give clear guidelines in regards to dustiness measurement and characterization to provide manufacturers and producers with information on the potential for dust emissions when materials are handled, processed or stored. In this way the standard can help handlers of bulk materials to reduce dustiness.
It gives the required guidelines for handling and working with the NOAA materials. The small rotating drum method has been designed to simulate workplace scenarios and to represent general bulk material handling processes, such as materials being poured, mixed, scooped, dropped or tipped.
The small rotating drum method presented in EN 17199-4 differs from the rotating drum, continuous drop and the vortex shaker methods.The rotating drum and small rotating drum methods both perform repeated pouring and agitation of the bulk solids material.
The small rotating drum (SRD) method measures the dustiness of bulk materials in terms of the respirable dustiness mass fraction, the number-based dustiness index, the number-based emission rates and the time period it takes to generate 50% of the emitted particle number.
The SRD method has been applied to test powders, granules or pellets containing or releasing respirable NOAA or other respirable particles in either unbound, bound uncoated and coated forms.
The SRD methods measures a range of materials including nanoparticle oxides (such as TiO2 and SiO2) and nanoflakes, organoclays, clays, carbon black, graphite, carbon nanotubes, organic pigments, and pharmaceutical active ingredients.
The method has been proven to enable testing of many different materials that can contain nanomaterials as its main component.