Safety Systems Group (SSG)

The Safety Systems Group (SSG) is responsible for the three systems in support of operations at accelerator, experimental end stations and other facilities at Jefferson Lab:

  • Personnel Safety System (PSS)
  • Machine Protection System (MPS)
  • Oxygen Deficiency Hazard (ODH) monitoring system

The Safety Systems Group provides the Personnel Safety Systems and the Machine Protection Systems on the accelerator site. Other areas protected by a PSS include the Vertical Test Area (VTA), the Injector Test Stand (ITS), and the Cryomodule Test Facility (CMTF).

Where necessary, monitoring systems are installed in the areas to mitigate oxygen deficiency hazards (ODH).

The group is involved in research in the use of programmable electronics for safety applications. Its expertise extends to risk and reliability analysis, fail safe design, programming techniques, and development of standards and practices.

SSG Pesonnel

Supervisory Organization Chart
Essential Personnel
Design Authority List

Engineering Work Requests (Service Request and Problem Solving)


The Personnel Safety System (PSS), which is composed of sensors, interlocks, warning devices, and PLC (Programmable Logic Controller) is designed to protect personnel from exposure to prompt radiation that could be present during accelerator operations.

The PSS is composed of two autonomous systems – chains, A and B, which can independently sense a fault and shut off hazardous equipment. Each of the multiple, diverse methods receives redundant control signals from the PSS. In addition, two methods are used to shut off a magnet or RF power supply, and three methods are used to shut off the electron beam (i.e., multiple methods). To avoid common mode failures, each of the methods is implemented using a different technology (i.e., the methods are diverse).


The Machine Protection System (MPS) is a hardware-based system used to shut off the electron beam in cases where sustained beam, or energy directly related to the electron beam, could damage beamline components. The MPS hardware network receives “trip” signals from around the machine, and directs them to outputs to devices capable of shutting-off the beam. The MPS receives inputs from target motion monitoring, beam loss detectors, superconducting cavity arc/quench detectors, vacuum valves monitoring etc.

The backbone of the MPS system is the Fast Shutdown system (FSD), consisting of the fiber connected network of the FSD interface cards, which has the ability to shut off the beam from anywhere in the accelerator in less than 40ms. The actual detection of a fault condition and the interface from the fault logic to the FSD system is the responsibility of the end user.

The MPS is composed of sensors, interlocks, and warning devices, which are designed to prevent or minimize damage to accelerator equipment.


The purpose of this system, usually referred to as the ODH System (Oxygen Deficiency Hazard) is to monitor the oxygen level in areas where there is a potential for oxygen displacement by other gases typically used in accelerator operations. This system is intended to function as an engineered control measure to mitigate ODH hazards and enables staff to work in a safe environment.

The most commonly used gases at Jefferson Lab are helium, which is lighter than air or ceiling-seeking gas and nitrogen, which is heavier than air or floor-seeking gas. When released to atmosphere, these gases, which are typically used in a liquid or compressed state, can expand up to 700 – 800 times their liquid volume, therefore, even a small leak may lead to an oxygen-depleted condition in a confined area. Exposure to reduced oxygen levels adversely affects human body functions and may cause reduced abilities, unconsciousness, or death.