Some food manufacturers have reservations about the adoption of x-ray inspection as a method of product inspection. They are concerned that their staff will object to bringing x-rays into the workplace and that consumers could switch to another brand that hasn’t been subjected to x-ray inspection. People are cautious about radiation, but that doesn’t mean they should be worried about the use of x-rays in food inspection.
The levels of radiation used for x-ray inspection in the food industry are extremely low, and the use of x-ray inspection equipment is both highly regulated and increasingly common. Food manufacturers use x-ray inspection technology to ensure product safety and quality, and x-ray inspection gives them exceptional levels of metal detection for ferrous metal, non-ferrous metal, and stainless-steel. The technology is also extremely good at detecting other foreign bodies such as glass, mineral stone, calcified bone, and high-density plastics and rubber compounds.
In addition, x-ray systems can simultaneously perform a wide range of in-line quality checks such as measuring
mass, counting components, identifying missing or broken products, monitoring fill levels, measuring head space, inspecting seal integrity, and checking for damaged product and packaging.
This chapter covers the health and safety aspects of radiation, and puts permitted radiation limits in the context of everyday exposure to different radiation sources, both natural and man-made.
Energy from a given source is generally referred to as ‘radiation’ – and different forms of radiation have been harnessed by science for use in many different types of equipment that we now take for granted in everyday life.
There are two main sources of radiation: natural and man-made. Examples of both types of radiation include natural heat or light from the sun (and beyond), radiation from the ground, and gamma rays from radioactive elements. Man-made radiation includes microwaves from an oven and x-rays from an x-ray tube.
Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing procedures, in which matter can be studied and characterised through the use of radiation. X-rays are used for many purposes, from medical examinations to the identification of contaminants in foodstuffs and other materials.
X-rays used in food inspection systems should not be associated with radioactive materials such as uranium. Radioactive materials are physical sources of radiation, and they emit radiation in the form of alpha particles, beta particles, and gamma rays. They do so continuously, which is why they cannot be switched off – and the only way to contain radiation from a radioactive material is to encase it in a substance (such as lead) that absorbs radiation.
X-rays used in food inspection are different; like light from a bulb, they can be turned on and off at will. Switch off the electricity supply to the x-ray system, and the flow of x-rays ceases instantaneously.
To understand radiation levels, it is important to compare dose rates from some natural and artificial sources of radiation that we are exposed to in day-to-day life.
Each member of the world population is exposed, on average, to 2400 µSv a year of ionising radiation from natural sources. Typically, this far exceeds the radiation exposure received from a properly installed and maintained x-ray inspection system.
The irradiation of food doesn’t cause it to become radioactive, just as a person doesn’t become radioactive after having a chest x-ray.
Food irradiation, which is regulated by the FDA (the USA’s Food & Drug Administration) and WHO (the World Health Organisation), involves exposing food to a radiant source, such as x-rays. The benefits include extended shelf-life, improved product quality (because ripening is delayed) and reduction in the number of micro-organisms present. A WHO study in 1997 confirmed that food radiation levels up to 10 kGy (10,000 gray) did not affect its safety or nutritional value.
The ‘gray’ (Gy) is a measure of the absorbed dose of radiation, and is defined as the absorption of one joule of radiation energy by one kilogram of matter. One gray is equivalent to one sievert.
The FDA doesn’t regard a dose below 1 kGy as an irradiation process. For example, to kill salmonella in fresh chicken requires a dose of up to 4.5 kGy, which is about 7 million times more radiation than a single chest x-ray. The radiation dose received by objects scanned by an x-ray system is typically 200 µGRAY (i.e. 200 micro-grays, each micro-gray measuring a millionth of a gray) or less – a level that is too low to affect the safety or nutritional value of food. Organic food producers, and others who may be concerned about the implications of irradiation, will be reassured to know that this low-level dose is less than background radiation, and has absolutely no effect on the food product.
In the UK, the Food Standards Agency (FSA) conducts independent nationwide reports on radioactivity in food. The survey measured radioactivity from different parts of the food chain, including radioactivity levels applicable to people who live close to nuclear sites and eat local food.
The FSA combined this data with radiation levels from possible exposure to other authorised radioactive discharges. The report found that the total UK dose is under the EU annual dose limit for members of the public. That annual dose limit is 1 millisievert (a thousandth of a sievert) for all exposures to radiation.
X-ray radiation has practical uses in medicine, research, and product inspection applications, where it can be used safely for many valuable purposes. However, if utilised improperly, it can present a health hazard to humans.
It’s sometimes assumed that any dose of radiation, no matter how small, is a health risk. However, there’s no scientific evidence of any health risk at doses below 20,000 µSv a year, which is the adult limit for occupational radiation exposure when working with radioactive material.
Modern x-ray systems for food and pharmaceutical applications don’t contain sources of live radiation, such as uranium; in fact they are designed to provide a perfectly safe working environment for operators. Provided safety guidelines are followed, there are no restrictions for anyone, including pregnant women and young adults, operating this type of equipment.
The x-rays within an x-ray inspection system are electrically generated, which means they can be turned on and off. This differs from radiation sources (such as uranium), which naturally emit radiation in the form of alpha, beta or gamma rays. These sources can only be made safe by proper containment.
To protect the user from the effects of radiation, x-ray inspection systems are safe because they have been specifically designed with safety in mind. That’s why they are designed with the x-ray generator installed in an enclosure; this is known as a ‘cabinet system’.
It’s still worth bearing in mind that the risk of being exposed to radiation can be controlled through a series of protection principles: time, distance and shielding.
X-ray Inspection System Safety
When using x-rays for product inspection, the x-ray system must be built to comply with safety standards such as the Ionising Radiation Regulations 1999 and the American Standard 1020.40 CFR. Meeting safety standards ensures that all personnel and production staff are safe when operating the machine, providing everyone follows the safety procedures. For this reason, x-ray inspection systems should be built utilising the following safety requirements:
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