Aerosol Anatomy - The Aerosol Laboratory Part 2By: John Chadwick
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The series began in April 2006 with Part 1, which covered basic concepts relating to the installation of an in-house aerosol laboratory, including: the functions and advantages of the on-site lab; factors to consider in selecting a suitable location; various safety systems built into the infrastructure; and, the basic equipment required to crimp and charge single aerosol units. Part 2 addresses outfitting the lab with basic and optional equipment, and, also explores routine quality control testing of samples made in the aerosol tab.
At a minimum, the charging of flammable propellants should occur in an explosion proof (XP) hood. This hood, as well as the surrounding area, should be equipped with propellant leakage monitoring equipment installed and calibrated for the flammable propellants to be used in the lab. A new XP hood unit may be installed in an existing lab space, or, an existing hood may be upgraded to the XP requirement by replacing the electrical components, lights and fan motor with the appropriate XP counterparts. Note, however, that appropriate safety procedures must be followed when filling any aerosol product.
The gas monitoring-detection-alarm system typically consists of a control unit and one or more gas detection heads located in the hood and at floor level around the hood. Flammable hydrocarbon gas is heavier than air, and the system is designed to monitor gas build-up at the floor level. The system includes alarms (both audible and visual), which are activated when a relatively low level of explosive gas is detected.
This first stage activation alerts personnel to shut down the equipment immediately and look for the source of the leak, possibly a loose pressure hose connection, poor can crimps, or a faulty gas valve.
MSA and Bacharach are two suppliers of gas monitoring and alarm systems. System design and pricing are quite variable depending on the options selected and the specific location to be monitored. An on-site visit by the supplier's sales representative can be arranged to ascertain specific needs. (An additional description of the operation of these systems can be found in the previous article in this series.)
Another "typical" fixture in the aerosol lab is a spray booth. Regardless of the type of aerosol product, all spraying should be done inside a vented enclosure to contain and safely exhaust aerosol fumes. If propellant charging is conducted in an XP hood, and the hood is large enough, this component may be able to function as both a gassing area, as well as a spray booth.
The advantage in this scenario is that the gas detection system and the XP rated components of the hood will service both functions. An additional utility requirement is a cold water feed for clean-up of the spray collection system, which deposits product run-off into accumulation containers for later disposal. Depending on the products being evaluated, several accumulation containers may be required, such as individual receptacles for water-based products, oil-based products, paints, insecticides, etc.
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