Subsections

• • Equipment Hazards
  • Equipment Hazard Mitigation
  • Hazards
  • Hazard Mitigation

Cryogenic and Oxygen Deficiency Hazards

Equipment Hazards

The energy stored in the HMS superconducting quadrupoles is sufficient to cause an unrecoverable quench if all the energy stored is dumped into the magnets. The same is true for the Møller superconducting solenoid. The HMS dipole has been designed to achieve cryostability up to a field of 2 T, and this property has been extensively tested up to a field of 1.11 T. Note that a quench can only happen if the superconducting magnets have their helium level dropped below the coil, and their coils energized.

Equipment Hazard Mitigation

In all cases quench protection circuit are incorporated. The dipole cryostable coils are equipped with an energy removal circuit to cover the possibility of an unrecoverable quench.

Hazards

Contact with cryogenic fluids presents the possibility of severe burns (frostbite). The release and subsequent expansion of cryogenic fluids presents the possibility of an oxygen deficiency hazard. Rapid expansion of a cryogenic fluid in a confined space presents an explosion hazard. Cryogenics in Hall C are present in the superconducting HMS magnets, the scattering chamber with its cryogenic targets ($\sim$12,000 STP liters of hydrogen), and the Møller superconducting solenoid. In the case of the superconducting HMS magnets and the cryogenic targets the ODH hazard is minimal, apart from the area above the Hall C crane. The Møller solenoid contains $<$2000 STP liters of target fluid. However, this solenoid is located in the alcove thus enhancing a possible ODH hazard.

Apart from cryogenic fluids, the gas in the HMS and SOS gas Cerenkovs pose also a potential oxygen deficiency hazard for access inside these detectors.

Hazard Mitigation

Normally accessible areas of Hall C are listed as an Oxygen Deficiency Hazard area of Class 0. No unescorted access is allowed without an up-to-date JLab ODH training.

All volumes in the cryogenic systems which can be isolated by valves or any other means are equipped with pressure relief valves to prevent explosion hazards.

All issues concerning the safe operation of both the HMS cryogenic magnet system and the Hall C cryotarget systems were reviewed by outside panels.

No one may enter the Cerenkov tanks while there is radiator gas inside these tanks. The tanks should be pumped out and filled with air before access to the interior of these tanks is permitted. Possible leaks do not impose an additional hazard, e.g the total enclosed volume of the SOS Gas Cerenkov is 30 cubic feet, while the air conditioning unit in the hut replaces the air at a rate of 1100 cfm.

The responsible personnel for access to an ODH-area are the principal contacts for the JLab EH$\&$ S group:

Bert Manzlak

- x7556 (Physics EH$\&$ S )

Charles Hightower

- x7608 (Physics EH$\&$ S )