Characteristics of biological aerosols in dairy processing plants

The viable aerosol in dairy processing plant environments was characterized by using an Andersen six-stage sieve sampler and a Reuter centrifugal sampler. Artificially introduced Serratia marcescens were detected in the air during drain flooding and after rinsing the floor with a pressured water hose, thus illustrating the ability of a specific microorganism to be disseminated from drains and wet surfaces via physical disruption activities often observed in food plants. Once a high concentration of wet viable aerosol was generated, it took 40 or more min to return to the background level in the absence of forced ventilation or other activity. The greatest reduction in viable particles occurred during the first 10 min. Estimated mean aerosol particle sizes were decreased from approximately 4.6 to 3.2 mu with time lapse. The estimated mean aerosol particle sizes from actual dairy processing plant environments ranged from approximately 4.3 to 5.3 mu. In addition, a more heavily contaminated dairy processing environment contained larger aerosol particles. These results indicate that the RCS sampler will often overestimate the true aerosol concentration in highly contaminated air, because mean particle sizes are over 4 mu in diameter.