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Privacy and Security Notice

Tour Safety

Jefferson Lab Environmental, Health & Safety Manual
Chapter 3230: Communication of Hazards to Visitors

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. Please review the advisory messages below. For more information, visit:

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.

Oxygen Deficiency Hazard advisory
Some areas that tour groups enter are classified as ODH or Oxygen Deficiency Hazard areas. These areas have equipment or pipe-transfer systems containing cryogens, or liquefied gases that expand greatly - should they be accidentally released they will return to their gaseous state. These cryogens could displace all of the oxygen in a given area, should a release happen. Although the probability of death due to this happening is very small (<1 in 10,000,000), visitors need to be aware of the following ODH warning/danger alarm signals:
A blue strobe light
A loud buzzing alarm
A visible white plume or indoor fog bank

If any of these occur, quickly leave the area WITH your escort, making sure not to pass through any plume. If your escort is lost or unconscious, go out the nearest EXIT, making sure not to pass through any plume. DON'T try to remove any unconscious person from the area. Go to the nearest phone and dial 5822.

Radiation Control area advisory
Most of Jefferson Lab's ODH areas are enclosed within the accelerator, its three separate experimental halls, and the Free-Electron Laser 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. So wearing dosimetry is required for entry into the accelerator, experimental halls and FEL. Tour groups are assigned one radiation dosimeter for every five visitors.