The Challenge of Investigating the Dust Explosion Properties of Nano-Powders and Highly-Active / Highly-Toxic Substances

The safety laboratories of the Swiss Safety Institute in Basel (former Ciba-Geigy and Sandoz) perform since more than 30 years explosivity, combustibility and thermal stability tests on chemical substances in dust form.

These substances are often irritant or toxic. However the standard tests to determine the dust explosion relevant properties defined by the international norms are very frequently associated with an open handling of the material, at least for weighing samples. Up to now the high laboratory safety standards of the European pharmaceutical and chemical industry had proven to be effective in the health protection of laboratory technicians. However new industrial developments may require higher safety measures due to the need to perform safety tests on e.g., nanoparticles, synthesis intermediates and active pharmaceuticals ingredients. The particles of these materials may cause health damage in very low concentrations in the air, an open handling is not recommended.

Many standard methods for safety tests of chemicals involve open handling of substance. For highly toxic or highly active substances, new test methods and equipment are therefore necessary.

The Swiss Safety Institute has developed such test methods and has validated them against acknowledged standards.

 A new safety concept was developed in order to solve these problems. It is based in the combination of two technical solutions:

•  Development of tests methods that reduce or eliminate the open handling of substances
• Use of working stations, where the remaining open handling can be performed safely

 Examples of new developments:

• Closed Hartmann Tube for the determination of the Minimum Ignition Energy (MIE) of dust clouds
• 20 litres Sphere for the determination of Explosion Characteristics of Powders
• Screening for Self-Ignition (DSC under 5 bar of oxygen; equivalent to the basket test)
• Decomposition test with simultaneous recording of pressure in an autoclave
• Friction and Impact sensitivity under closed conditions.
• Powder resistivity / conductivity
• Charge relaxation time

With these new test methods the substances are enclosed completely. The transfer of the sample into the test equipment or sample tubes is done under laminar flow conditions in special laboratory work stations. After the test, the substance is either burned directly inside the equipment, washed out in place or the sample tube is sent for incineration without opening.