July 2014 SPRAY 79 meriting a paradigmic transition to alternative technologies. In the U.S., the DOT has approved special exemption petitions wherein BOV nitrosols can be checked for proper pressure by a device that measures the minute deflection of the can body wall when a horizontal force is applied. Deflections are compared with those of a same specification can containing a known pressure. Such lines can avoid the use of a hot tank, although most will have a small one (usually a drum type) for leak detection and a final rinse. In Europe, a different regimen has emerged. Empty cans are tested on a rotary machine to at least 67% of their design pressure to ensure that they do not deform when filled or leak at a rate of less than 0.033 mbar.liter/sec. Filled cans must be check-weighed so that overfilled cans can be rejected. Finally, another rotary machine is used to briefly enclose all filled cans and reject those that leak at a rate greater than 0.002 mbar.liter/sec. at 68°F (20°C). These steps are required by the road transportation agency Accord European Relatif le Transport International of Dangereuses por Route (ADR), whether the aerosols are hot tanked or tested by alternative means. The criteria established by the ADR (2007 Section 6.2.4.3.2.2) have been presented to the U.N. Subcommittee of Experts on the Transport of Dangerous Goods. They have supported the regimen, noting that a micro-leak detector would be required on the filling line to assure 100% inspection. These devices, which cost about $10,000, would have to be installed on every line. While these detectors would work for hydrocarbon detection, provided the air between the water level and sensors is tranquil and not ventilated, it is doubtful that they would work for non-flammable HFC-134a and HFO-1234ze(E), or for water soluble propellants like carbon dioxide and dimethyl ether. They would certainly not work for aerosols pressurized with nitrogen, argon or compressed air. Through the efforts of the FEA, the EEC Aerosol Dispenser Directive (75/324) has been modified through its Adaptation for Technical Progress (ATP) 2008/47/EC to permit “alternative methods” to hot tanking aerosols. In effect, these documents support the production of aerosols with alternatives to hot tanking and their transportation to all EU countries in dispensers carrying the reversed epsilon. The U.S. DOT has now been approached to adopt equivalent regulations in the interest of global harmonization. In the U.S., serious questions have been raised regarding the maximum leakage rates, such as 0.002 mbar.liter/sec. This standard, while scientifically correct, must be converted to more easily understandable terms to be more useful. The first conversion is that it connotes a seepage rate that would raise the pressure in a one liter container by 0.000002 atmosphere per second (1.00 bar equals 14.5 psi-gor the average pressure of 1.00 atmosphere at an altitude of about 400 feet). Considering a 1.00mL container, the pressure gain would be 0.002 atmosphere per second. Similarly, a theoretical 0.002mL container would be pressurized to 1.00 atmosphere—or the gas pressure inside a propellant bubble. This equates to a 0.126mm cube, equal in volume to a 0.134mm diameter bubble. For a hot water bath moving aerosols at 6" (152mm) per second, one gas bubble 0.134mm or 0.0053" in diameter would have to be detected every 6". If a bubble escaped once every 24" (608mm), at the same seepage rate it would be equal in volume to a 0.200mm cube or a 0.248mm (0.0098") diameter sphere. Similar calculations can be made to clarify the maximum allowable seepage rate for empty cans in the pressure tester; i.e 0.033 mbar.liter/sec. It is very doubtful if visual observation in hot tanks could reliably detect seepage rates as low as the 0.002 mbar. liter/sec. limit now imposed in Europe. In a specific test conducted recently, only about 8.4 cans per million were found to be leakers. All were slow leakers, passed by a weigh-checker. Considering there are up to 60,000 cans per truckload, that would equate to about one leaker or less in every two truckloads, if not detected in the hot tank or by alternative processes. This is far less than the leakage needed to produce any significant hazard, regardless of propellant selection. The superb transport safety record of U.S. aerosols supports this conclusion, especially since, of the billions of dispensers produced and shipped each year, it is inevitable that some will have been undetected slow leakers. SPRAY References 1. Guide to Hot Water Bath Testing & Its Alternatives, FEA, (32 pages), 2009. 2. The Aerosol Handbook, Second Edition, by Montfort A. Johnsen, 405-6, (1982). Available in electronic form from Spray Technology & Marketing. 3. European ADR, Sections 6.2.4.3.2.2.1, 6.2.4.3.2.2.2 and 6.2.4.3.2.2.3 (2007) for international road transportation in E.U. countries.
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