Air Quality Factors to Consider when Choosing Compressed Air Systems
The process of choosing appropriate compressed air systems for pharmaceutical applications comprises a number of selection criteria, all of which contribute immensely to air quality and equipment performance.
A major factor affecting final air quality is the appropriate selection of equipment, since compressed air is generated on site by the pharmaceutical manufacturer. For process applications where air is an ingredient in the process, such as blanketing or fermentation, a risk-based assessment is recommended to determine the critical air quality attributes. Maximum allowable levels for moisture, particulate (viable and nonviable), and hydrocarbons (oil in vapour and liquid) are to be established in the design.
An example of a risk-based approach may include an assessment of compressed air that is exhausted into a clean room. The air would be required to have the same air quality as the air already present in the clean room.
Once the attributes are defined, equipment selection begins. One error in design is defining user requirements as per equipment ratings. For example, a filter which is rated at 0.01 mg/m3 can become the attribute to be measured. This creates undue pressure on the facility to generate maximum 0.01 mg/
m3 contaminant, whereas air quality is considered sterile at 0.2. While 0.01 rating exceeds the requirement, it allows for filter loading, fouling, and changes in temperature and pressure, which affect filter performance. Typically, equipment selection includes, as a minimum, the compressor(s), dryer(s) and filters. Air-storage devices and distribution systems are also included, but will not be addressed here.