Explosion risks and safety hazards of nanomaterials
14 March 2012
An article entitled Review of the Explosibility of Nontraditional Dusts in the American Chemical Society journal Industrial & Engineering Chemistry Research by a team from Dalhousie University in Canada claims that nanomaterial dust could explode from a spark with only 1/30th the energy needed to ignite sugar dust, or less than 1/60th the energy required to set wheat dust aflame.
The researchers looked into the explosion risk of three types of non-traditional dusts: nanomaterials; flocculent (fibrous or fuzzy) materials used in products such as floor coverings; and hybrid mixtures of a dust and a flammable gas or vapor.
After reviewing results of the relatively few studies that exist on the topic, the researchers concluded that the energy needed to ignite nanomaterials made of metals, such as aluminum, is less than 1 mJ, which is less than 1/30th the energy required to ignite sugar dust
Dust is defined as a solid less than 420 microns in diameter, but that would not usually extend down to the nanoscale world. A general rule of thumb in the world of dust research holds that the smaller the particle size and the greater its surface area, the more explosive it is. Nanoparticles are tiny, but have a large relative surface area because of the way atoms are arranged in them. They also tend to agglomerate together, and these large clumps of nanoparticles, called nanopowders, are also very explosive, igniting with just 1 millijoule of energy. They could ignite with a spark, a collision or mere friction, according to the researchers.
Also, because they are so small, nanoparticles can remain suspended in the air for days or weeks without any obvious evidence of their presence.
Flocculent dust also usually does not fall under the normal definition of dust, but the researchers say this too is dangerous. Flocculent materials are often manufactured using electrostatics, so they also could easily ignite.
The third category, hybrid mixtures, behave in a more variable way, according to the Dalhousie team.
The article concludes that significant research is still needed into dust explosions in industry, especially of non-traditional dusts.
Meanwhile, a report entitled 10 Years of Research: Risk Assessment, Human and Environmental Toxicology of Nanomaterials by a joint DECHEMA/VCI working group in Germany, has also looked into the risks of nanomaterial use.
In the report, experts from industry and research institutions compiled a 60-page update on the current status of safety research in the area and give an overview of national and European projects on the safety of various nanomaterials, both for humans and the environment.
They conclude that at present, no extraordinary risks are known. The researchers point out that the ‘nano’ size label does not in itself represent an intrinsic hazard characteristic; instead, the impact of nanomaterials depends on other factors as well, such as the nature of the material. However, newly developed nanomaterials have to be submitted to a risk assessment just like any other new product.
The researchers call for increased toxicology and safety research into nanomaterials, based on international standards.