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Balanced Pressure Differentials and High-Speed Doors
While clean processing areas are routinely kept at a positive pressure, one of the keys to contamination control within most processing plants is creating a negative-pressure environment in the first stage processing areas. Effectively maintaining this condition through maintenance and facility design -- including air-handling systems and doors that connect process areas -- presents an ongoing challenge that all plants face in providing a safe processing environment. The first trick is finding a way to maintain that negative-pressure condition in the relatively "dirty" areas in poultry processing, for example, such as receiving, shackling and evisceration. If you picture 20,000 frantic birds entering the process each day, amidst a flutter of high-pressure water sprays and rotating picking equipment, it's easy to see where the problem starts. Preventing this dirty, moisture-laden air from entering the clean portions of the plant is critical. Though so much attention is focused on the cleanliness of tools, tables and processing equipment - and rightfully so - airborne pathogens can't be ignored. Fortunately, the negative pressures, created by large exhaust fans (12,000 to 50,000 cfm) in the picking, evisceration and scalding areas remove most of the bioaerosols before they have a chance to contaminate product as it's processed and packaged. When all ventilation systems are working as designed and the pressure differential is balanced, fresh air will flow from hygienic, pressurized meat cutting and packaging operations to exhaust fans in areas where bioaerosol emissions are contained. Unfortunately, there are dozens of variables that can disrupt this flow and allow the airborne contaminants (potentially including Listeria Monocytogenes, Escherichia Coli and Salmonella) to find their way out into the plant. Even "fresh air" intakes, located too close to areas where bird holding trailers are parked, can introduce humidity, molds, bacteria and bioaerosols as well as fertilizers and herbicides from nearby fields. Facility and system improvements The selection of construction materials for clean rooms and processing areas is a critical procedure, and if owners are not selective, they may unknowingly build sources of contamination into their own facilities. Maintenance plays a vital role in maintaining a proper balance of pressure and airflow as dirty or defective fans can also disrupt the original airflow and pressurization design scheme. Similarly, any holes, vents, leaks or openings in interior or exterior walls will create problems as well. When you consider the amount of worker and product movement, at docks and between processing rooms, it's also easy to see the role that doors (especially those that open to the outside) play in maintaining proper pressures and clean environments. Outside air infiltration It's important to note that common, overhead, perimeter doors frequently leak (500 cfm per exterior door is typical) due to sealing deficiencies, internal pressurization and wind. And, when they're left open too long, either from neglect, slow operation or for comfort, the inward flow capacities can permit air infiltration of 18,000 cfm - or more, depending upon internal pressurization, wind direction and velocity. To provide an alternative to the slow, overhead "garage doors" that frequently leak air, manufacturers like Rytec Corporation (Jackson, WI), offer a variety of high-speed doors that minimize potential air infiltration time. Quick opening time and full perimeter sealing help prevent air infiltration caused by winds or negative internal pressures. High-speed doors are an economical yet effective alternative to other more advanced and expensive contamination control methods. Cross contamination reduction High-speed door activation is an advantage for inside applications as well. Not only do shorter "open times" speed transportation of product between processing areas, they also help maintain the proper pressurization of each area. It's totally logical that faster door speeds will limit the migration of airborne contaminants and ultimately play an important role in protecting food quality and safety. And in the processing/packaging areas, where hygiene is most critical, you should look for doors with stainless steel components and fully washdown surfaces. The Clean-Roll® door (opens and closes @ 32 inches/second) features stainless steel construction and USDA/FDA-compliant panel material; it's also classified by UL, to meet hygienic standards for food, chemical and pharmaceutical applications. Other standard features that are essential in this environment include a stainless steel run-off trough to prevent accumulation of water and bacteria as well as a severe-duty, food-grade washdown motor with USDA-grade oil. Monitor plant air quality. Talk to the specialists. Since plant designs, as well as their internal and external operating environments are subject to constant change, it's important to make routine air sampling (of all preparation and processing areas) a standard component of your HACCP program. Plant management should also work with professional engineers to optimize HVAC systems while enforcing air handling equipment maintenance and operating procedures. For a complete report describing the importance of "Ventilation of Poultry Slaughtering and Processing Plants" contact Dr. A. J. Heber, Purdue University Cooperative Extension Service, West Lafayette, IN, 47907 (request Building Ventilation Series "BV-2"). For additional information on high-speed doors for food, chemical or pharmaceutical processing facilities, contact Rytec Corporation, One Cedar Parkway, Jackson, WI 53037-0403. |
