TOPIC 5: Administrative Controls & Levels

Let’s explore Administrative Controls & Levels.

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Working with radiation requires controls to protect workers and the public from inadvertently entering a radiation area.  The controls define the areas where radiation exposures may occur.  There are several levels of control.

The dose rate concept is crucial to defining levels of control and establishing perimeters. Dose rate tells us the dose received per unit of time and gives us an idea of the intensity of the radiation. We know that dose is directly proportional to the total time spent in the radiation field. We can make some cautious assumptions about how much time people could possibly spend there, and then calculate a dose rate limit that is protective of human health.

For example, if radiographers are examining pipes in an area frequented by members of the public, we want to keep the public doses well below the annual limit of 100 mrem. We know that the job will take far less than 50 hours to complete and members of the public are not likely to spend 50 hours on site, so a dose rate based on 50 hours will be conservatively protective of public health. So, 100 mrem divided by 50 hours equals 2 mrem/hr dose rate. Since we already know that the exposure to the public will actually be far less (< 10%) than 50 hours, the allowed dose rate of 2 mrem/hr will deliver a public dose that is far less than 100 mrem.

The source strength of the device used by the radiographers is known, so we can calculate the distance from the source where the intensity will decrease to 2 mrem/hr, and we set up a perimeter with warning signs at that distance.  We also make sure people do not loiter in the area.

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A controlled area is defined as any area under positive control of the company.  An example of the control would be a fence, a gate keeper (security guard), or a locked door.  The controlled area would normally be the workplace.  Any area where the general public is not allowed and is controlled, would be considered a controlled area.

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A restricted area is defined within the controlled area.  This area is restricted to individuals who work with the radioactive material.  Access to this area generally requires training and the permission of the Radiation Safety Officer (RSO).  An additional requirement of access to the restricted area may be the use of a dosimeter or radiation measuring equipment.  A restricted area is entered with permission only.

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A radiation area or Radiation Controlled Area is defined, in the regulations, as being within the restricted area and is an area that results in an individual receiving a dose equivalent in excess of 5 mrem in 1 hour at 30 centimeters from the source.  30 centimeters is about one foot.

While the 5 mrem/hour is the regulatory limit, an ALARA limit for a radiation area is the possibility of exposures exceeding 2 mR/hr.  The rationale is that if any non-radiation worker is in or around a radiation area that has 2 mR/hour exposure rate, and they frequent that area for one hour per week, that is 50 weeks/year X 2 mR/hour/week = 100 mrem/year – the annual dose limit for member of the public.

Access to this area is also restricted by the RSO. If work is to be done in a radiation area by a radiation worker, the RSO determines whether a special Radiation Work Permit detailing conditions and restrictions, such as the level of PPE and whether a personal monitoring device is required.  This protection factor is to be approved by the regulatory agency.

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A high radiation area (HRA) is any area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 100 mrem in 1 hour from any source.  This type of posting is used in extremely hazardous exposure areas.  Industrial radiography or Non-Destructive Testing (NDT) uses high activity sources with no shielding that can generate high radiation areas.  When these areas are posted, it requires an assistant to roam the perimeter to keep employees from inadvertently venturing into the area while the work is being performed.

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Signs are required to notify everybody of the presence of radiation.  Signs vary in size and shape but have several common features.  The signs are yellow and the radiation symbol, the trefoil, must be present and colored magenta.  The trefoil is the internationally accepted warning sign for radiation, and it looks like a propeller with three blades.  It also looks like my body.

Here are signs for Radioactive Material, Radiation Area, and High Radiation Area.  Any location that contains radioactive material must have a sign mounted to be easily visible that warns individuals of the presence of the radioactive materials or a potential radiation are.