More than the people or the equipment, the one element virtually guaranteed to contact food during processing is the air inside the plant. Indoor air can become the vector that delivers contaminants to food and food contact surfaces. HVAC systems are critical control points (CCPs) in ensuring that food production remains safe from pathogens, allergens and other airborne contaminants.
Explore this issueApril/May 2005
In-plant air quality must be managed as part of the HACCP program. As FDA advises in its 21 dFR 110.20 document, the food processing plant and facilities shall “locate and operate fans and other air-blowing equipment in a manner that minimizes the potential for contaminating food, food-packaging materials, and food-contact surfaces.”
Best practices incorporate a consistent program to test and monitor interior air quality, including regular testing for levels of airborne particulates. Airborne particles may include allergens or other food contaminants, such as dust from deteriorating lead paint, and particles that can carry disease-causing microorganisms.
Regular air quality testing, including the use of hand-held particle counters to monitor particulate levels, can help ensure that changing conditions are detected early and emerging problems are dealt with before production is disrupted or, even worse, contaminated product reaches consumers.
Keeping the Outside Out
Sanitary design to control airborne hazards starts outside of the facility. Any contaminants found outside of the plant, such as insects, rodents, birds and windborne microbes contained on dust particles, are liable to enter. Outside air may contain high counts of particles carrying microbes, and particle concentrations indoors tend to “track” those outside.
The FDA identifies maintenance of the plant and grounds (trimming weeds, maintaining roads and parking lots and providing adequate drainage) as an important factor in preventing contamination. Best practices in food plant operation prevent the intrusion of outside air. Doors and windows must be kept closed and loading doors must be closed or, during operations, sealed to limit the entry of contaminated air, insects, birds and rodents.
In addition, air inside the plant should be maintained at a higher pressure than outside. The HVAC system is managed to draw in some outside air, condition and filter it and pump the filtered air into the facility to maintain positive pressure. Inside air will prevent contaminated outside air from entering through any gaps, or when doors or windows are opened.
Best practices in sanitary design and operation of HVAC systems emphasize maintaining positive air pressure, air filtration to remove particulates, and maintaining the system to prevent microorganism growth.
Incoming air must be filtered. Many plants use standard spun-glass or low efficiency filters, which only capture up to 35 percent of particles 50 microns (µm) or larger. Particles 10 µm or greater in size typically settle out of the air stream, so such filters do little to remove smaller airborne particles.
Increasingly, food plants use HEPA filters that are 95 percent efficient at 5 microns (µm). This level of filtration will remove many dust particles carrying microbes and will also trap most allergens in recycled air.
The HVAC system must be properly maintained to prevent air quality problems. Particles generated inside a processing plant are often organic in nature, providing a food source for microorganisms. These particles may settle in ductwork or collect on fan blades and cooling coils. The right combination of temperature and humidity can contribute to the rapid growth of bacteria and/or mold, and turn the HVAC system into a breeding ground for contaminants.
Indoor Air Diagnosis
Identifying and solving indoor air quality problems before they become costly require a consistent and methodical approach to air quality testing and diagnosis.