LEAK TESTING OF AEROSOLS
All filled aerosol cans are leak tested before distribution to prevent an empty or near-empty product from reaching the patient. Four methods are currently used for leak testing.
- Hot water baths are maintained at temperatures above the boiling point of the product, such as 100°F. More common temperatures are 120–130°F, since the time to raise the can contents would be shorter. At least 1.5 to 3 minutes are required to bring the can contents to a temperature that would emit propellant vapor in a leaky unit. Cans are examined visually by inspectors who look for the presence of faulty crimps, valves, and so on. The emergence of bubbles signifies a probable reject. Protection from possible dangerous discharges should be taken. Filtered tap water has been used to test for leakage because the water does not come into contact with drug product. Currently companies are trying to use recirculated and filtered purified water in combination with ultraviolet lamps to minimize the microbial bioburden in the water. Various types of defects usually arise from poorly crimped valves (process defect), where bubbles appear from the side of a valve skirt or ferrule. Other rejects may be due to poorly assembled valves (valve defect), where leakage from the side of stem may occur.
- Induction heaters, in which cans are quickly heated and check weighed at a later time, heat the units instantaneously on the aerosol line after filling and crimping. Any faulty units or poor crimps would burst upon testing and be removed from the line. Subsequent check weighing is usually performed and any intact units that are leakers are removed. Induction heaters were introduced as an improvement over the visual inspection method. Storage of the filled units for a set period of time has become the most commonly used method for leak testing. Units are held for a sufficient period of time so that leakers will fail a subsequent check weighing step. Fourteen to 28 days have been used to ferret out faulty units. Inventory considerations have to be taken into account with this process requirement. Also, the probability that slow or latent leakers will pass undetected must be considered.
- Storage for a predetermined time period before check weighing.
- Pressure readings are designed to check the integrity of componentry before filling. This was designed to check the tightness of the crimp, which could be used later for performance evaluation.