Visitor Safety Information

Visitor Safety Information

We hope your visit with us is both safe and enjoyable. Most of the areas you visit at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) will not expose you to radiation above normal background levels. However, you may be exposed to radiation if you enter a Radiologically Controlled Area (RCA) or handle radioactive material.

Some of the areas where you may encounter radiation are listed below. Briefly passing by or through these areas will not expose you to measurable radiation if you respect the designated boundaries as posted.

Jefferson Lab is classified as a low-hazard facility. This means the hazards encountered here are comparable to those typically found in an industrial setting. There are a few places on-site where minimal personal protective equipment (PPE) is required: hard hats, safety glasses, solid shoes (no open toes or high heels on tours), or hearing protection. All visitors must comply with posted safety notices and the instructions provided by their escort/tour guide.

When scheduling a tour, consider the mobility needs of your group. Many facilities available for tours do not have elevators. Individuals touring these facilities must be able to walk down and back up several flights of stairs, be able to navigate group transportation easily and walk/stand comfortably for the entire length of the tour.

Microwave and RF-Radiation Advisory

Microwave or radiofrequency radiation is usually well contained at Jefferson Lab. Slight leakage, however, could interfere with instruments and electrical apparatus, including medical devices such as heart pacemakers. If you wear a pacemaker or other sensitive electronic biomedical equipment, please consult your personal physician prior to entering microwave or radiofrequency areas at Jefferson Lab.

Strong Magnetic Fields Advisory

Jefferson Lab has a few areas (predominantly in the accelerator tunnel and the experimental halls) that contain strong magnetic fields. Venturing into these magnetic fields could pose safety hazards to individuals with implanted surgical and/or bioelectronic devices (e.g. cardiac pacemaker, heart valve implant, ear implant, aneurysm clip, joint replacement, etc.). If you have metal in your body, you should consult your personal physician prior to entering areas at Jefferson Lab that contain strong magnetic fields. Sources of metal include, but are not limited to residual metal flecks in the eye from past accidents, shrapnel, surgical clips, pins, or other objects or devices that are implanted surgically.

Access to these areas is controlled, visitors are escorted, and they receive a safety awareness briefing before entering these areas.

Radiation Control Area Advisory

Most of Jefferson Lab's Oxygen Deficiency Hazard (ODH) areas are enclosed within the accelerator, its four separate experimental halls, and the Low Energy Recirculator Facility (LERF) vault. These areas are also posted as radiation control areas. When these areas are running, large amounts of X-ray radiation is produced. The radiation stops when the machine is turned off, but there is always a very small chance of exposure to small amounts of residual radiation. Wearing dosimetry is required for entry into the accelerator, experimental halls and LERF. Tour groups are assigned one radiation dosimeter for every five visitors.

 Possible Radiation Exposure Areas

  • Continuous Electron Beam Accelerator Facility (CEBAF) and various locations and buildings inside the CEBAF site fence, including the tunnel and end-stations
  • Low Energy Recirculating Facility (LERF) - Building 18, inside the CEBAF site fence
  • Test Lab - Building 58, specific areas within the building
  • Experimental Equipment Laboratory (EEL) - Building 90, specific areas within the building
  • Calibration Range - Building 54

Radiation Safety Guidelines

To minimize your exposure to radiation while at Jefferson Lab, simply follow these three guidelines:

  • Minimize your time around radioactive materials and radiation-generating equipment
  • Maximize your distance from sources of radiation
  • Use shielding whenever possible

In addition, please do not handle radioactive materials or bring any radioactive materials or sources onto the Jefferson Lab property.

    Radiological Postings

    Upon entering the CEBAF site, you will pass a large sign reading Controlled Area.

    After this point, you must be with your escort at all times.  He/she will ensure that you do not go into any areas that are hazardous.

    Do NOT enter the following areas, even with an escort

    • Radiation Area, High Radiation Area, Very High Radiation Area
    • Contamination Area, Airborne Radioactivity Area
    • ODH-2, ODH-3, ODH-4 Areas
    • Confined Spaces

    All areas containing radioactive materials, radiation producing machines, or creating a measurable radiation level are clearly identified by various signs and labels. Each sign has the following characteristics:

    • The international symbol for radiation
    • Yellow background with magenta or black writing
    • Special instructions, if applicable

    Below are some examples of radiological signs at Jefferson Lab:


    Yellow and magenta rope is often used to designate the boundaries of radiological areas. 

    Individual items stored within a designated RCA do not need to be labeled as radioactive. It is important to consider all items within an RCA boundary as radioactive. Do not remove anything without specific permission from the Radiation Control  Department.  Radioactive material which is transported or stored outside an RCA must be controlled through the Jefferson Lab Radiation Control Department's inventory system and must be appropriately labeled. 


    A dosimeter is a device which monitors the amount of radiation to which you are exposed. The areas into which you may enter are routinely monitored, and are not expected to expose you to any measurable radiation.

    If you are given this dosimeter, you are being monitored for an official record. You must still be escorted, but you are allowed to work in an RCA and on radioactive materials, with your escort’s direct observation.

    If you are given this dosimeter, you may access RCAs with your escort, but you are NOT allowed to handle any radioactive materials or perform any radiological work.  Please do not press any buttons on the electronic dosimeter.

    Notify your escort immediately if:  

    • You drop or bump your dosimeter
    • Your dosimeter goes off scale or appears to malfunction
    • Your dosimeter starts alarming

      Your Risks

      Acceptance of a risk is a highly personal matter. It requires a good deal of informed judgment. The risks associated with occupational radiation doses are considered acceptable as compared to other occupational risks by virtually all the scientific groups who have studied them. The following chart may help put your potential risk from exposure to radiation into perspective based on the potential number of days of life lost.


      Fetal Exposure

      An embryo/fetus is especially sensitive to radiation. For radiological workers, limits are established to protect the embryo/fetus from any potential effects which may occur from a significant amount of radiation exposure. Such an exposure could be the result of exposure to external sources of radiation or internal sources of radioactive material. The probability of any effects occurring in the embryo/fetus from occupational exposure is small. For a visitor, the probability is infinitesimally small. In addition, you should know that the children of occupationally exposed personnel have no known increase in birth defect rates.

      ODH Briefing

      Some areas that you may enter are classified as Oxygen Deficiency Hazards (ODH).  They may contain cryogens (liquid gases) that expand greatly when they turn into gas. When this occurs, the cryogens can replace all the local oxygen supply.  Although the probability of death due to such an event is very small (<1 in 10,000,000 per hour), you need to know the danger signs.

        If you see a blue strobe light, a white plume, or hear a loud buzzing alarm, quickly leave the area with your escort, making sure not to pass through the plume. If your escort is lost or unconscious, go out the nearest exit, making sure not to pass through the plume - do NOT try to remove any unconscious people from the area. Go to the nearest phone and dial 911 or 5822.

        Do not enter ODH-2, ODH-3, or ODH-4 areas, even with an escort.

        Safety/Emergency Information

        You have a right to know about all the hazards you may encounter while at Jefferson Lab.  If you have further questions, please call the appropriate number.

        Radiation Safety

        • Radiation Department Manager (757) 876-5342
        • Field Ops (757) 876-1743
        • Dosimetry (757) 269-7236

        Non-Radiation Safety Issues

        • ES&H Division (757) 269-7277

        Emergency Phone Number

        • 911


        • x5822 or (757) 269-5822