Fire and explosion hazards during handling and use of nano dusts

Status:

completed 01/2015

Aims:

Objectives of the project are to determine and review, in which industries, plants and processes risk of fires and explosions during the handling of nanomaterials may occur, whether during the handling and production of nanomaterials a greater risk can be assumed than for micro dusts and to derive safe operating parameters. Furthermore it is intended to create the necessary preconditions for a safe determination of the fire and explosion characteristics of respective dusts. Therefore it is necessary - depending on different test methods - to change or improve experimental apparatuses and sample preparation with respect to health protection and avoidance of changes in particle size distribution compared to the condition at time of sample collection. The burning and explosion behaviour could be affected by agglomeration (or coagulation) in a way which might lead to an underestimation of the real hazard potential. Both explosion hazards of dust dispersed in air as well as hazards of dust deposits, such as fires as a result of spontaneous combustion have to be considered.

Activities/Methods:

Potentially endangered areas were investigated and assessed. Furthermore the work was focused on the investigation and determination of the fire and explosion behaviour of most critical dusts with particles produced within the nanometer range. Therefore first tests concerning health protection and suitability of test equipment were carried out. Based on the insights gained a glove box system was designed, that allows the examination of dusts within the nanometer range.

For the fire and explosion experiments various metal dusts produced within the nanometer range (aluminium, iron, copper, zinc and titanium), carbon nanotubes as well as a cellulose dust (micron particles with shares of nanometer particles) were chosen. With the tests the most critical fire and explosion behaviour of nanometer dusts should be determined. This means that all measures have been taken to avoid the contact of the test dust with oxygen before the start of the experiment.

Obtained results show that even almost unpassivated nano dusts do not show a higher explosion severity (maximum overpressure, maximum pressure rise) than most critical dusts with primary particles within the micrometer range. However, the investigated nano copper is flammable and explosible. In addition, the influence of passivation (oxidation of the particle surface) on the fire and explosion behaviour of metal nano dusts was investigated.

Results:

The test results clarify that contact with oxygen for a short period of time (several minutes) does not significantly change the obtained safety characteristics. This means that the standard test methods for determining fire and explosion characteristics of micrometer dusts are also applicable for the nanometer dusts that have been tested – at least down to the particle sizes that have been investigated.

With decreasing primary particle size especially unpassivated nanodusts can react very ignition sensitive. For smaller particle sizes than those tested in this work (below 50 nm) more materials might react pyrophoric.

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