change of density, fracturing and other changes can occur during flight, whether in the ambient air or in the lungs. As one more example, the drug Ribovarin at 1.27 microns swelled to 3.4 microns in the nose and then to 4.5 microns in the lung, due to humidity. The tiny size of the drug particles permitted these expansions to be almost instantaneous. Many technicians have only a general idea of the huge numbers of particles and the enormous increase in surface area that can result from the spraying of just 1mL of an aerosol product. From the basis that a 1mL cube produces eight 0.5mL cubes, 64 0.25mL cubes, 512 0.125mL cubes and so forth—this last having all sides 125 microns long—it follows that a typical 31.3-micron diameter spray would have 62,582 particles. Considering that the 31.3-micron diameter is the arithmetic mean, there would be millions of particles smaller than this size. Lastly, some would be thousands of times heavier than others. Solid particles are particularly challenging, since they come in all shapes and sizes and rotate in all three dimensions. Platelets sometimes stick together. Filamentous types, like carbon, may be a hundred times as long as they are wide. Some form clusters as they react to humidity. The “diameter” of oddly shaped solids can be controversial. Metal oxide pigments can have high densities, leading to such perplexing concepts as aerodynamic particle size. While the vast majority of aerosol products do not affect the human pulmonary system in any way, even if abusively used, regulators and nongovernmental organizations (NGOs) (both in the U.S. and Europe) are now considering safety measures that may include the PM-2.5-micron particle size limits. This article illustrates the many complexities in realistically determining this rather elusive parameter. Spray SEM microphotograph of a drug substance with a mean diameter of 2.4 microns. Therapeutically useful range 1.0 to 6.5 microns. Particle edges emphasized for better contrast. REFERENCES Particle & Fibre Toxicology, Donaldson, K. and Seaton, A., PubMed Central, 6-MAY-2012. Understanding Ultrafine Particles Indoors, Nazaroff, W.W., Air Pollution Seminar, California Air Resources Board, 2-FEB-2010. (Auspices of the University of California, Berkeley.) The Importance of Particle Size to Spray Hazard Analysis,Virden, A. Spray Technology & Marketing, 41, MAY-2014. GRIPPER SERIES HOT WATER LEAK TEST TANK INLINE SERIES WITH OPTIONAL PLC CONTROLLED CHANGEOVERS Terco, Inc. 459 Camden Drive, Bloomingdale, IL 60108 U.S.A. | Tel: +1 630-894-8828 | www.terco.com sales@terco.com March 2016 Spray 25 AUTOMATED PLC CONTROLLED PRODUCT FILLING MEASURING CHAMBERS AUTOMATED PLC CONTROLLED PROPELLANT CHARGER MEASURING CHAMBERS
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