IIndustrial Ecological Park (see Ecological Parks)

Industrial Ecology (see Ecological Parks)

Inlet Ducts and Silencers (see Acoustic Enclosures, Turbine; Air Filtration; Ducting)

Instrumentation (see Condition Monitoring; Measurement)

Insulation (see Some Commonly Used Specifications, Codes, Standards, andTexts)

Irradiation, Food Product*†

The push to improve food quality through irradiation began early in the 20thcentury, when researchers aimed newly discovered X rays at foodstuffs to preservethem. In the 1950s, the availability of manmade isotopes such as cobalt-60, used tosterilize medical equipment, changed the course of food irradiation. Gamma raysemitted by the isotope were able to destroy pathogens in food as effectively as moreexpensive technologies such as an electron accelerator. Since then, the techniquehas been applied to such items as poultry, fruits and vegetables, and spices.

For example, in 1986, a company called SteriGenics began irradiating dry-foodingredients such as pepper, onion powder, and dehydrated vegetable powder atfacilities in Tustin, Calif.; Schaumburg, Ill.; Rockaway, N.J.; and Salem, N.J. Theseplants irradiate approximately 50 million pounds of spices annually. The companywas founded in 1979 to sterilize single-use, disposable medical products such assyringes and gowns.

The spices arrive at SteriGenics plant warehouses in bulk form in bags anddrums, or sometimes in their final form in boxes. Workers affix dosimeters, such asthose made by Far West Technology in Goleta, Calif., on the containers beforeloading them into metal containers or totes. The totes are loaded onto carriers thatare suspended from an overhead monorail to move them into an irradiatingtreatment cell. The cell walls and ceiling are 61/2-feet-thick concrete poured aroundsteel rebar to ensure that no crack can penetrate the walls. See Fig. I-1.

The totes are exposed to gamma rays with short wavelengths, similar toultraviolet light and microwaves, emitted from an array of cobalt-60 “pencils”installed on either side of an 8- by 16-foot stainless-steel rack. The pencils areactually stainless-steel tubes containing two zircon alloy tubes that encapsulatenickel-coated pellets of cobalt-60. When the pencils are not in use—duringmaintenance, for example—they are submerged in a 26-feet-deep pool of deionizedwater, more than twice the depth needed to protect maintenance workers when thearray is submerged, and raised when irradiation recommences.

A U-shaped overhead conveyor in the cell guides the totes until they are exposed

I-1

* Source: Adapted from extracts from “Keeping Food Germ Free,” Mechanical Engineering, ASME,March 1998.

† Note: Financial figures in this section reflect known costs and prices in 1998.

for a timed interval to the desired absorbed dosage of gamma radiation, a maximumof 30 kilograys for spices. (A gray, measuring the absorbed dose of ionizing radiation,is equal to 1 joule per kilogram.) The treated totes are returned to the warehouseon the other side of the conveyor dividing the loading and unloading operations.The spice containers are removed from the totes and shipped to customers.

SteriGenics retrofit its Tustin plant in 1996 to treat low-dose foods requiring lessthan 1 kilogray of radiation: “fresh vegetables, including avocado, onions, celery,bell peppers, and broccoli, that are sold either for retail sale or as ingredients forother products such as a salsa.” The shelf life of fresh produce irradiated at Tustinis extended by up to two weeks.

Palletized Loads

The year before SteriGenics began irradiating food, FTSI, another American foodirradiator, was formed because the Florida Citrus Commission sought analternative to methyl bromide as a quarantine treatment for citrus. The agency wasacting on an Environmental Protection Agency suggestion that methyl bromide,used to prevent the spread of fruit flies, would be banned in 2001.

The company treats several truckloads of packaged agricultural products perweek for both local and national brokers and distributors. These foods are sold toretail establishments and institutions. The food-irradiation industry is based onpublic health concerns, such as food poisoning, rather than economic benefits,according to some, although such economic benefits do accrue, specifically byextending shelf life and serving as a quarantine measure. The process eliminatessprouting in tubers such as potatoes, garlic, and onions, for example. Irradiationalso delays the ripening of certain fruits and vegetables, including strawberries,tomatoes, and mushrooms, which are the main crops treated at FTSI.

As a quarantine measure, irradiation kills the larva of insect pests such as fruitflies and seed weevils in mangoes, preventing them from spreading betweengrowing regions. Irradiation can also be used to pasteurize seafood.

FTSI’s irradiator and safety control system were designed and built by MDSNordion in Kanata, Ontario, a major supplier of cobalt-60 as well as a designer ofmedical-sterilization plants and research-irradiator equipment.

The MDS engineers used their own controls and interlocks for the FTSI safetysystem, which also included radiation monitors, restricted openings, and aprocedure to replace cobalt-60 pencils underwater with magnifying lenses andmanipulators. Several hundred different conditions will automatically shut downthe system in case of component failure or system inconsistency.

Unlike the process loops at other facilities, FTSI can irradiate large pallets ofpackaged foods. MDS engineers had to build a plant that would handle the heavierloads than their earlier systems could. This involved scaling up the 48- by 24-inconveyors used in facilities like the Canadian Irradiation Facility in Montreal to 48by 42 in to handle U.S. pallet sizes. This involved testing monorails, bearings,wheels, and I-beams to build an overhead conveyor that could transport the 2-tonloads in a single carrier. They also used hydraulic cushions to gently stop the largerloads, and built forklift clearances so the pallets could be loaded and unloaded fromthe carriers.

These carriers are 18-feet-tall, 4-feet-wide, 4-feet-deep aluminum boxes holdinga shelf at floor and mid-level. Forklift operators load a pallet on each shelf of thecarrier. The carriers are transported from the warehouse into the 61/2-feet-thickconcrete treatment cell via a pneumatic overhead monorail. Once inside, hydraulicsmove the carriers, primarily because greater locational accuracy of movement isrequired; this also reduces the number of cylinders needed to carry the heavy loads.

I-2 Irradiation, Food Product

As in the SeriGenics process, the FTSI carriers follow a U-shaped trajectory inthe treatment cell that exposes them to gamma rays from cobalt-60 pencils. Theexposure time in the concrete cell and other process parameters is directed byOmron programmable logic controllers.

After being irradiated, the carriers return to the warehouse on the other side ofan interior chain-link fence that separates the two halves of the irradiating process.The pallets are removed by forklift and placed on trucks for delivery.

Irradiation’s Future

The most likely scenario for plant construction in the future is building dedicatedfood-irradiation plants either at or as near as possible to the point of transportationand distribution, after the final packaging and labeling is complete, to prevent thepossibility of recontamination after irradiation.

Location is important, especially because rising freight costs could exceedirradiation costs. (An increase in gasoline prices could also affect the economics ofirradiation.) Relatively few plants for FTSI, each estimated at $10 million to $12million, would suffice. For example, a well-built, well-located spice plant could treatup to 150 million pounds of product a year.

Food irradiation is a technology whose time has come, until a better alternativeis found, because food inspection and testing are revealing more incidents of food-borne disease.

Accelerating Irradiation

Only two companies—SteriGenics International in Tustin, Calif.; and Food Technology Service Inc. in Mulberry, Fla.—irradiate food in the United States, andboth use the same basic process involving cobalt-60 isotopes. Linear accelerators,however, may be the technology of future plants. These devices emit a beam ofelectrons that directly contact the product or convert the accelerated electrons intoX rays, which can penetrate deeper than an electron beam but are less efficient.

Most linear-acceleration operations opt for showering the product with electrons.The Utilization Center for Agricultural Products at lowa State University in Amesuses this technique. A meat scientist and director of the center is conducting food-irradiation experiments on meat products with a Circe 3 irradiator built byThomson CFE in Saint-Aubin, France (see Fig. I-2). The center’s work is sponsoredby the U.S. Army, the Agriculture Department, and the Electric Power ResearchInstitute in Palo Alto, Calif., with grants from meat producers’ groups including theCattlemen’s Association and Pork Producers.

The device is used to address two major concerns facing linear-acceleratorirradiation. The first is to determine which packaging materials can be used inirradiation without causing compounds to migrate into the food. The second goal isto determine the optimum packaging environment for meat products beingirradiated—specifically, vacuum packing, a modified atmosphere such as nitrogenblanket, or oxygen.

The researchers load meat products onto carts attached to conveyor chains thattransport the carts through the 93/4-feet-thick concrete walls of the irradiation area.The floor-mounted Circe 3 contains an electron gun comprising a cathode and anodethat generate electrons, which are pulsed into an accelerating tube. At the sametime, radio-frequency power is pulsed into the accelerating tube by a klystron,forming waves for the electrons to follow.

A series of alternating magnets in the tube accelerate the electrons to the highenergy levels required for irradiation. When they reach the end of the tube, the

Irradiation, Food Product I-3

electrons pass through a Glaser lens that focuses them into a beam. The beam isbent by a magnet to a 107° angle, so only the particles of the selected energy levelare emitted. Those filtered electrons pass through a scanning magnet and sweepacross the meat’s surface, changing the DNA of microbes in the food and killingthese pathogens.

Three different energy levels can be selected: 5 million, 7.5 million, and 10 millionelectron volts, which can penetrate 3/4 in, 1 in, and 1.5 in on one side, respectively,or 13/4 in, 21/4 in, and 31/2 in if both sides are irradiated. Some electrons are pickedup when irradiating both sides, which is why the penetration is more than double.

I-4 Irradiation, Food Product

FIG. I-1 A worker at the SteriGenics irradiation facility in Tustin, Calif., loads drums of spices ontocarriers that will be transported to an irradiation cell to reduce the presence of microbes in thefood. (Source: “Keeping Food Germ Free.”)

FIG. I-2 Dennis Olson conducts research using a Circe 3 linear accelerator to irradiate meatproducts at lowa State University. (Source: “Keeping Food Germ Free.”)

A multilayered safety system is used at the Ames irradiation facility, startingwith the maze through which the carts are conveyed—three 90° turns that serveas a biological shield, preventing electrons or X rays from ricocheting to the product-handling area. This and other safety devices are wired to the control panel and tothe Circe 3. If one electric path fails, the other will trip the electron source and shutdown the facility.

Irradiation, Food Product I-5