One of the major avenues for the entry of contaminants into a facility is through the gaps between the dock leveler and the dock walls.

The Bug Stops Here

Plugging the points of entry against infiltrating contaminants helps food facilities ensure a safer product.

For years, the food industry has tried to control product quality and safety of food products by focusing on three primary factors: (1) the quality of the initial food materials, (2) the "cleanability" of the processing equipment, and (3) the quality and cleanliness of packaging materials. All of these factors affect the spread of pathogenic microorganisms that can spoil food and make it dangerous to consume.

Microorganisms can be transported around a food plant in many ways: Water spray during the cleaning process, employees and plant visitors, and plant drains are just a few sources of transmission. Food quality degradation also can be caused by the transport of microorganisms through the air.

For years, industry placed too little importance on the possible factor of airborne contamination. "The food industry is now coming to realize that the air in and around a critical process area, which comes into direct or indirect contact with the food product, is a possible vehicle for the spread of pathogenic organisms," said Bruce Paulson, an engineer with Evapco Inc.

Airborne contamination can result in product returns, damage to a company's reputation and market share, and increased regulatory surveillance. The Centers for Disease Control and Prevention estimates approximately 87 million people suffer from food poisoning each year; 371,000 become so sick they require hospitalization, adding severe cost to our already overburdened health care system.

As much as possible, processing plants and food handling operations attempt to set up a closed-circuit operation to prevent or at least minimize exposure of food to the air during processing. Certainly this can be achieved in operations where raw ingredients arrive packaged at a plant and are piped into the processing system. But for much of the industry, particularly the segment that deals with meat, the product is exposed through much of the process.

Limiting exposure means sealing up the building as much as possible. Dock doorways, measuring on average 8 feet by 10 feet, are big holes in the walls that provide big opportunities for pathogens to invade. Raw ingredients and finished product must be brought into and out of the building as efficiently as possible.

The air in and around a plant contains not just nitrogen and oxygen, but also "dust." Atmospheric dust is a complex mixture of smokes, mists, fumes, dry particles, and natural and synthetic fibers, among other light inorganic particles. When suspended in a gas, this mixture is called an aerosol. This aerosolized "dust" can transport living microorganisms such as molds, bacteria, pollens, yeasts, and viruses. In the air, individual microorganisms typically cannot grow or multiply because of the absence of nutrients, but they can be transmitted by air currents for long distances. If this aerosol finds its way into the processing area, the food product becomes that nutrient.

In critical process areas, infiltration -- the exchange of indoor air with either outdoor air or air from an adjoining space -- is a big deal. For infiltration to occur, two conditions must be fulfilled: (1) there must be an opening or crack in the building envelope, and (2) there must be a pressure difference between the two sides of the wall at that location. Pressure differentials can be caused by wind, temperature differences between rooms, and process exhaust equipment or stacks, either in the critical process area itself or in other areas in the plant, such as the dock.

Some openings are obvious: doors, conveyor openings, and other necessary wall penetrations. Other openings or cracks are less obtrusive, such as small openings around doors and windows and cracks in wall materials and roofing.

The dock affords many opportunities for contaminants to enter a building. The functionality of loading dock equipment has evolved over the years, primarily in the interest of worker safety. Recently, energy concerns have begun to stimulate closer attention to how a facility outfits the dock. Today, the same initiatives for blocking energy loss can be applied to preventing the entry of contaminants into the building.

There are two major sites at the dock that need to be sealed: the perimeter gap between the pit leveler and pit walls, and the perimeter gap between the dock door and the doorframe.

Mind the Gaps
For typical docks, the perimeter gap between the pit leveler and pit walls and the open hinge gap on trailer swing-out doors can have a combined exposure of 3.63 square feet, on average. Dock levelers are necessary to allow forklifts to safely access truck trailers and to create the level interface between the warehouse and the trailer. Dock levelers are typically mounted in a concrete pit; however, that configuration creates small gaps between the edge of the dock leveler and the pit wall, exposing the facility to interior and exterior airflow exchange.

With a pit-style leveler, any breeze outside can be detected simply by standing over the gap between the floor and the leveler platform. Tightly closing the dock door all the way to the floor and installing standard neoprene or brush weatherseal does not completely cut off this airflow.

Both new and existing pit-style dock levelers can be outfitted with an advanced weatherseal system comprising a durable combination of open-cell foam and heavy-duty vinyl that effectively fills the gaps around the sides and rear of the dock leveler, providing a superior seal around the dock leveler perimeter. Although microcontaminants are an issue, this sealing system also closes off an avenue of entry for insects and vermin, which too can be carriers of microcontaminants.

The pit-leveler seals are effective when the leveler is stored and not providing access to the truck trailer and throughout its working range. These systems are designed to avoid the risk of being cut, torn, or damaged by trailers or debris to ensure the seal remains effective.

For the trailer, hinge gap dock seals are critically important. Dock seals have fabric-covered foam pads that compress when the trailer backs into them, providing a tight seal around the sides of the trailer and sealing off the gaps between the trailer's door hinges. Dock shelters consist of fabric attached to side/head frames to create a canopy around the full perimeter of the trailer; they allow full, unimpeded access to the interior of the trailer.

Galvanized steel backing offers many advantages over wood backing that is used on some models. Wood backing has a solid mass (1.5 inches thick) that does not yield when the seal is compressed. This often results in damage to the building. On steel backing, the solid mass is replaced with compressible foam on a steel frame. Steel backing also offers superior durability because it does not rot, split, crack, or warp. It uses plated screws with load-spreading washers in the steel to provide a stronger, more durable hold on the fabric.

Though largely regarded as a safety device, the vehicle restraint also plays a role in helping to seal off the dock doorway. Many docks use rubber wheel chocks in an attempt to hold trucks in place during loading and unloading. However, rubber chocks are no match for the forces exerted by forklifts driving in and out of trailers.

This force can gradually cause a trailer to "walk" away from the dock, forming a doorway gap. A powered truck restraint ensures the trailer is held snuggly to the dock, with the back end of the trailer fully enveloped by the dock seal.

Moisture is a vehicle that allows contamination to enter the dock area; droplets can remain airborne until they eventually settle on a product. Dock seals and shelters can be combined with rain-sealing systems that literally wipe off moisture from the roof of backing trailers to keep it out of the dock area. These rain-sealing systems attach to the top or header of the dock seal/shelter; they are fitted with a wiper pad that sweeps rain, snow, and condensation off the roof of the trailer.

Dock Door Defense
The combined exposures for the perimeter gap between the dock door and the doorframe on typical docks can average 2.71 square feet. Even though the door is closed, the building envelope may not truly be sealed. On busy docks, forklifts moving product often hit and damage the door or the door track. Though a damaged door requires immediate attention, a partially damaged door may still function, yet it allows gradual energy loss. Even a slight bump can cause the door to be misaligned and the resulting gap, however slight, can lead to a significant infiltration of outside, microcontaminant-bearing air.

Impactable dock doors are the first line of defense. These doors are built to stand up to the occasional bump or the most severe collision. Rather than becoming damaged from the force of a major impact, the door panels release and can be easily set back in place. Fully impactable models have the door seal attached to the door panel rather than the doorframe. The door can roll up, taking the gasket out of harm's way, to maintain a consistent seal.

The use of dock equipment by food processors has always been about safety. Now this policy of caution can be applied to the safety of the workforce, the consumers who buy the product made within the facility, and the reputation of the company making the product.

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  • OHS Magazine Digital Edition - January February 2021

    January February 2021


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