We utilize a central vacuum conveying system (like those from Conair and Novatec) to move dry material. If you know how this type of system works, feel free to skip the next paragraph; otherwise, read on for an explanation.
When the receiver needs material, the sequencing valve opens the receiver to the vacuum air flow. The vacuum line turns on, drawing material and air flow into the receiver. Pleated filter media (cartridge filters) in the upper portion of the receiver separates the material from the conveying air. This then directs the material downward into the cone of the receiver. When product is called for from the receiver, the discharge valve opens and gravity allows the material to flow out of the receiver. A blowback system directs accumulated, high-power blasts of compressed air through the cartridge filters, pulsing the filters and blowing off collected material, dust and fines to encourage total material evacuation from the receiver.
The compressed air that pulses the filter cartridge is at the heart of the issue. It is not used to dry or move the material. Presumably if air goes in as the vacuum is created to pull the dry material into the hopper, one would think it would go the other way when the air system is pulsed. The exposure to product is not absent, but limited to whatever was on the filter cartridge itself.
The compressed air system has two filters in series on the compressed air going to the plant. The first filter removes particulate to 1 micron and oil vapor to 1 ppm. The second filter removes particulates to 0.01 micron and oil vapor to 0.01 ppm.
We received a minor on a recent SQF audit for not checking the purity of the compressed air. Given this information, would a risk assessment be acceptable in the eyes of an auditor and/or a certification body? I'll likely spend more time writing the RA than it would take to test the air on a frequency to be defined, but this seems like it may be a worthy challenge.