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Shutting the Door on Pathogens
by Kurt Angermeier
Most of our food travels a long way from the farm to the dinner plate. The most crucial yet controllable part of that route is within the four walls of the food processing plant. After raw food hits the delivery dock at the processing facility, it can travel hundreds of feet through various rooms as it is transformed into packaged product. Food can be exposed to any number of contaminants at critical control points.
Pathogen Air Raid
Airborne microorganisms represent a serious threat to quality and safety as product moves from one part of the processing plant to another. According to a study commissioned by the American Society of Heating, Refrigerating, and Air Conditioning Engineers and conducted by Dr. A. J. Heber of Purdue University’s Department of Agriculture and Biological Engineering, these bioaerosol emissions may be carried throughout a processing plant via airflow through doorways and other openings. Dealing with these doorways can reduce the flow of contaminated air and mean additional benefits for the food operation as well.
An aerosol is the suspension of fine solid or liquid particles in gas. Bioaerosols are airborne contaminants that include bacteria, fungi, viruses, and pollen. These free-floating microorganisms may be present in the air as solids (dust) or as liquids (condensation and water) and they are an important bacterial vehicle.
In their paper “Controlling Airborne Microbial Contamination,” Chris Kerth and Crystal Braden from Auburn University state that “with air being considered a potential source of product contamination, the avenues which can allow the air inside the facility to become contamination must be controlled.”
It’s said simple practices such as keeping doors closed is essential in controlling air contamination. That’s easier said than done. Doors with heavy traffic suffer from maintenance issues that arise from frequent usage and damage caused by crashes. Deficiencies in door design can mean that even when the door is closed, contaminants still find a way through. As a result, proper door selection becomes important in preventing contamination.
Doors—Passage and Protection
Walls and doors are used to separate clean and unclean areas, but improperly sealed doorways can defeat the protection these barriers provide. The door industry has engineered doorway solutions that minimize bioaerosol travel and transport as product moves through the process. These doors not only meet the demand for increased productivity and reduced maintenance costs, but also satisfy compliance standards set forth by Hazardous Analysis and Critical Control Points (HACCP) and other food safety programs.
In order to contribute to bioaerosol flow suppression, doors should offer the following measures of protection.
Leaving Microbials Behind in the Rush. According to Dr. Heber, “the speed at which a door operates definitely could affect dispersion or movement of bioaerosol emissions to clean rooms in a food processing operation.“
Slow operating doors compromise quality and safety by enabling dust and fumes to travel with the forklift between areas. Slow speed can also reduce control over desired temperatures, threatening food quality. The faster a door operates, the more effective it serves as a barrier.
Rapid door operation means that food is not only moved faster along the process, but it is moved safer. Seconds count when it comes to outracing bioaerosols while maximizing efficient product handling. For an 8-foot high door that opens at speeds up to 100 inches per second, the doorway will be open for as little as 5 seconds as the forklift hurries through.
High-speed doors and minimal opening time mean doorways are closed as much as possible, maintaining air balance.
Protection All the Way Around. A tight seal on all four sides of the door panel is as crucial as the seal on product packaging. The optimal roll-up door barrier consists of full-height seals enclosed by the side guides and brush or vinyl seals along the header and bottom bar. If seals prevent air infiltration and energy loss, pathogens can be stopped at the door.
This seal is compromised when the door is hit by a forklift. The doorway could be unprotected for hours until the repair crew arrives or for days if there is panel damage. Repairs can disrupt the flow of ingredients and products to the production and shipping areas, especially if there are few doors into the room.
For a high-speed door, the rapid opening should make these occasions rare. But when collisions do happen, the door panel should have the capability to break away from its guide to prevent damage. The ability to quickly reset the door into the guides minimizes room exposure.
In this high-speed setting, high performance puts high demands on the door. Effective counterweight design eliminates stress and overworking of the door motor.
Clean Getaway. The door must be as easily cleaned and sanitized as all other processing equipment and containers used in the process. Like the equipment, the doors must be made of nontoxic materials, particularly if the doorway leads into areas designated as clean rooms.
These kinds of doors must meet the requirements for current Good Manufacturing Practices (cGMP) as defined under the Food, Drug, and Cosmetic Act, which dictates that equipment and utensils in food production areas must be chosen and designed to prevent disease and adulteration. Metal parts should be constructed of stainless steel, including the frame and the roll-up drum. Some models have removable frames for easy cleaning.
For roll-up style doors, nonporous USDA/FDA approved curtain fabric enables doors to easily shed dirt and debris during wash down. Door curtains should be completely extended when doors are closed, preventing microorganisms and debris from collecting around the drums.
Chasing Moisture Away. Major sources of contamination in food processing facilities are wastewater, rinse water, and spilled product that become aerosolized. Airborne bacteria, yeast, and mold are generated in processing facilities by heating, ventilation, and air conditioning systems. These systems contribute airborne microorganisms under normal operation because they provide fertile areas for growth due to moisture.
Sink and floor drains can harbor microorganisms because they are humid and contain nutrients from wastewater that provide a fertile growth environment. Flooded drains cause microorganisms on the surface to become aerosolized and air disperses them, causing increased levels of aerosolized bacteria in the food processing facility. High pressure spraying also causes an increased level of aerosolized bacteria.
Here’s where the door itself, especially a roll-up door, can sometimes become part of the solution yet part of the problem. The curtain plays an excellent role as a large catcher’s mitt for aerosolized microorganisms, blocking the entry of these invaders into the next step in the process. But these pathogens are rolled up with the door curtain as it opens. As product passes underneath the opening door, the bioaerosol can drip on the food below.
A roll-up door can be outfitted with a pneumatic drip-catch tray that moves under the roll drum when the door opens to prevent adulteration and contamination. When the tray is in place, contaminated liquid is stopped from raining on the food.
After traffic passes through the doorway, the tray moves out of the threshold and back to the original position, allowing the door to close. These trays do not interfere with efficient door operation, and they are the first line of defense in enabling compliance with cGMP, HACCP, USDA, and other regulations.
Because of floor drains and water accumulation from wash downs, the floor is a common source for bacteria growth and the roll-door bottom bar can make contact with these contaminant pools. As another measure of protection against this microorganism habitat and bioaerosols, manufacturers are adding a sloped bottom bar to their roll-up curtains. The design prevents water from dripping on product by channeling it off to the side of the doorway.
No Pooling. Walls that separate freezer areas must be properly insulated, as must the doors that cover the doorways leading into them. Doors that fail to minimize heat transfer can provide a cool surface on the warm room side of the door, turning the door panel into a condenser and creating water droplets and an environment for microorganism growth.
Whether the doors are solid panel or, for high-traffic doorways, roll-up style, the doorways must be insulated properly to handle the temperature differentials between the freezer area and the room outside. Even roll-up doors with insulated curtains do not equal the insulation provided by a solid wall. And with heavy traffic, these doors rarely stay closed for long. To minimize air infiltration, these doors must open and close rapidly.
When door are shut, curtains must provide some measure of insulation. When doors fill the role as vapor barriers between cold room and the warmer area on other side of wall, the operation enjoys the dual benefit of minimizing energy loss and reducing contaminated air infiltration.
An uninsulated door on this kind of a doorway becomes a condenser when the cold room chills the warm side of the door. When the door is closed for a period of time between accesses, moist air can hit the chilled panel surface. Water will form and then pool up on the floor. Not only does the pooled water create a pathogen breeding ground, but the slippery floor can lead to worker injuries.
No Admittance for Undesirables
As always in the real world of the plant floor, it is impossible to keep airborne bacteria, yeast, and mold in food processing areas at a zero level. Nevertheless, combating the assault of airborne contamination on food is a multifront war that processors fight with a variety of weapons.
Installation of recirculating air infiltration units, constant monitoring, consistent room temperatures, and even limiting employee traffic are among the many means to reduce contamination throughout the route to the shipping door. Though total confinement of pathogens to their place of origin is beyond practicality, proper door selection and application can ensure that food travels through the plant safely and that an unacceptable level of the microorganisms do not.
Angermeier is vice-president, marketing, for Rytec High Performance Doors. Reach him at firstname.lastname@example.org.