Experiment Safety Assessment Document
for the Base Equipment in Hall B



1.0   Introduction

Hall B is one of the three experimental areas at CEBAF. This manual attempts to describe the experimental equipment that makes up this facility, and to provide instructions for the safe and effective use of this equipment. In this operations manual, safety is addressed in the sense that proven procedures are provided. Responsible personnel are listed for each end station subsystem in Appendix.... of this document. The primary hazards are listed, and procedures detail how we address each of them.

2.0   General Issues

There are a number of potentially hazardous systems which are required at any accelerator complex. In this section we outline the extent to which these general site hazards effect the operation of experiments in Hall B, and list those which require special training. For more information on site safety systems and regulations the user is referred to the CEBAF EH&S Manual.

The principal contacts for the CEBAF EH&S group are:

  1. Bert Manzlak - x7556
  2. Charles Hightower - x7608
  3. Dennis Skopik - x7740

2.1   Oxygen Deficiency Hazard

Because of the presence of cryogens (for the CLAS superconducting magnets and for cooling the cryogenic targets) Hall B is listed as an Oxygen Deficiency Hazard (ODH) area of Class 0. This rating requires that those wishing to have unescorted access to the hall must take the CEBAF ODH training course once every two calendar years. This course is typically taught once monthly by a representative of the EH&S group. There are ODH alarms in the hall and blue lights. The alarms sound and the lights will flash if there is a potential ODH hazard. Further, those working above the crane railing must have more extensive ODH training as documented in the CEBAF EH&S manual.

2.2   Radiation Safety and the Personnel Safety System

CEBAF's high intensity, high energy electron beam is a potentially lethal radiation source and hence many redundant measures aimed at preventing accidental exposure of personnel to the beam are in place. This is the purpose of the Personnel Safety System.

The current status of Hall B is displayed in the Hall B counting house on a sign with red lighted letters. The possible conditions are:

Beam Permit   There is potentially beam in the hall.

Power Permit   In this mode all devices which normally prevent beam transport to the hall may be removed or energized. This is one level below that required for beam delivery. No personnel are allowed in the hall when it is at this level.

Sweep   The machine safety officers are securing the hall. No access is permitted during this process.

Controlled Access   Access is permitted only by using the keyed interlock system (A procedure for this type of entry is listed below).

Restricted Access   The entry gate to the hall is open, and trained personnel with appropriate dosimetry may enter.

If the hall is in either Beam Permit or Power Permit status, it is impossible for personnel to enter. If a situation arises that requires a hall entry, then the shift leader will call the Machine Control Center (MCC) and request an entry. The state of Hall B will then be lowered to controlled access, and a limited number of trained personnel can enter the hall via the two door entry gate from the labyrinth. It is required that personnel entering have a Jefferson Lab Radiation Dosimeter and be Jefferson Lab Radiation Worker qualified.

The controlled access procedure is as follows:

  1. Access to Hall B is allowed under a General Radiation Work Permit (GRWP). The GRWP specifies access requirements for areas within the Hall.
  2. The hall status sign in the counting house must read "controlled access." If not, the shift leader must call the MCC, and they will send a radiation survey team over to check the radiation levels in the hall.
  3. Proceed downstairs to the two door entry gate to the hall and call the MCC at extension 7050 before touching the door. Inform the MCC crew chief of your name and the names of those accompanying you and request that they open the outer door.
  4. Hang up the phone and enter the two door gate. The last person in should close the outer door after entering the gate area.
  5. Each person entering must take a key from the key bank and inform the MCC via the phone or intercom which key they have taken. The keys form a personnel accounting system, and all the keys must be in the bank for the hall to be returned to a beam permit state. Therefor, one should NEVER leave the downstairs area with a key. In addition to the individual key, there is a master key which must be removed from the key bank and placed in the master lock. This is normally done by the radiation officials who survey the hall.
  6. The MCC will need to see that all personnel entering have a Jefferson Lab radiation dosimeter. They verify this visually, and it is never permissible for both gate doors to be open simultaneously.
  7. After everyone has a key the inner door will be opened allowing entry into the tunnel leading to Hall B. The inner door must be shut behind the last person entering.
  8. When the work in the hall is complete you must either push the buzzer button by the inner door or call the MCC to get back into the gate area. The keys should be returned to the bank and the last person leaving must remove the master key from the master lock and replace it in the first position of the bank (This key is normally placed in the master position by the individual who first surveys the hall when it is opened for a controlled access).

While downstairs the status of the beam is visible on the yellow run-safe boxes. The lights should either be green or yellow. If the run-safe box in an area where you are working has a red light lit you should hit the "push to safe" button immediately.

If the hall status reads restricted access then there is free access for trained personnel.

2.2.1   Induced Activity

In addition to the hazard of direct exposure to the electron beam you must be aware of the potential for induced radioactivity in objects near the path of the beam. The GRWP specifies the requirements for hall entry after beam shutdown. Typically, a radiation survey is done to evaluate conditions in the hall. If radiation levels exceed certain thresholds, then specific signs, postings, and barriers will be installed by the RCG or ARMs. In addition, verbal instructions may be given to personnel in the area regarding access to various locations. In any case, always read radiological postings, and follow the instructions. If it is necessary to remove or modify beam line or target components, or to perform any work in a posted Radiation Area, you must consult the RCG before beginning work. In many cases a specific RWP (SRWP) is required for work. SRWPs for many activities will be available in the Counting House for review.

Any item which was in or near the beamline during beam delivery and needs to be removed from the hall must be surveyed by the RCG prior to removal. All hardware, materials, or components which are waste items from these immediate areas should be placed in the large blue drums available for potentially activated material. The RCG will survey these items before disposal.

2.2.2   Radiation Control Personnel

The radiation safety group at CEBAF includes the following personnel:

 

TABLE 1. Radiation Control Group

Name

Extension

Pager

Home Phone

Bob May

7632

680-7632

424-5525

Dan Dotson

7296

680-7296

1-804-693-9590

David Hamlette

7219

680-7219

766-3827

Earl Ratliff

7118

680-1682

1-804-642-1832

Geoffrey Stapleton

5059

680-2967

898-6726

George Walker

7417

680-7417

1-804-693-5146

Keith Welch

7212

680-7212

875-1707

Melvin Washington

6243

680-6243

599-0241

Scott Schwahn

7551

680-7551

564-1957

Zach Edwards

7147

680-7147

872-7519

2.3   AC Power

There are two Voltage levels of three phase, AC power service available in Hall B, 480Y/277 V and 208Y/120 V. These two voltages are available on four separate feeders.

The first feeder is distributed form the Hall B Truck Access Electrical Room and it is rated for 1200 A at 480Y/277 V. 280Y/120 V power is derived from this feeder for other low voltage uses via transformers. This feeder supplies utility loads in the Truck access Tunnel (lights, vent fans), the Beam Dump (lights and utility power in the Beam Dump Alcove) and the Experimental Hall (dome lights, vent fans, A/C fan coils and all receptacles mounted on the concrete walls of the Experimental Hall). Circuits from this feeder generally have a "TBxx" prefix identification mark. This power originates from a transformer located near SB1 (Bldg. 92. This transformer also supplies power to SB1 which furnishes chilled water for A/C and LCW in the Experimental Halls and cooling tower water for the End Station Refrigerator (ESR) Bldg. (Bldg. 102).

The second feeder is distributed form Hall B and is rated for 1800 A at 480Y/277 B. 208Y/120 V power is derived from this feeder for other low voltage uses via transformers. This feeder supplies loads to large magnet power supplies and to utility loads (lights, convenience receptacles and fan coils) on the steel structures (Space Frame, Forward Carriage, Clamshells and Pie Tower) located in the Experimental Hall. Circuits from this feeder generally have of two prefix identification marks; "SB ESB" or "B-UP." This power originates from a transformer is dedicated to Experimental Hall B.

The third feeder is distributed form Hall B and is rated for 800 A at 480Y/277 V power is derived from this feeder for other low voltage uses via transformers. This feeder supplies clean power to electronic loads on the steel structures located in the Experimental Hall and in the Beam Dump Alcove. Circuits fro this feeder generally have a "B-CP" prefix identification mark. "Clean power" should be used for noise sensitive applications such as power supplies for detectors. It is not permissible to power machinery or convenience outlets from the clean power. If you are uncertain about the use of AC power in a given situation, ask the shift leader or any Hall B staff member. `This power originates from a transformer located near the Counting House (Bldg. 97). This transformer also supplies clean power to Experimental Halls A and C.

The fourth feeder is distributed from the Hall B Truck Access Electrical Room and it is rated for 225 A at 480Y/277 V. This feeder supplies emergency loads in the Experimental Hall (lights and smoke removal fans) and in the Truck Access Tunnel (lights, smoke removal fans and roll-up doors). Circuits from this feeder generally have a "TBEM" prefix identification mark.

There are kill switches on each level of the Experimental Hall structures, which allow the power to be shut off in the vicinity of the switch. The power may be deenergized locally with a red mushroom switch or remotely in the Counting House.

There are many circuit breaker panel boards located around Hall B. If you encounter equipment that seems unpowered, it is always worth checking the status of the breakers in these panelboards. All outlets and disconnects in Hall B have a label that indicates the panel and circuit number of the branch circuit which sup9plies it. Aside from resetting of circuit breakers, you should not attempt to solve any other problems associated with the AC power distribution system without consulting responsible personnel.

Anyone working on AC power in Hall B must be familiar with the EH&S manual and must contact personnel responsible for the system.

2.4   LCW Operations

The low conductivity water (LCW)system for Hall B is located on the North wall of the Hall. The system has two outputs, one at 120psi for most power supplies, magnets and turbo pumps and another at 230psi for the Pair Spectrometer magnet and Møller Quadrupole magnets. The return pressure is typically 30-50psi on both the low pressure and high pressure lines.

2.4.1   Normal Operations

During normal operations the split of the input LCW into the low and high pressure lines is automatically controlled. The controller located on the North wall should read 125psi and be in automatic mode. If the LCW control system becomes unstable the pressure reading will fluctuate by more than 10 psi, this is unacceptable and Plant Services should be contacted immediately. Noise from the system can be reduced during restricted accesses by manually closing the large ball valve. This restricts the flow into the low pressure system before the automatic diverting valve, and lowers the amount of noise the diverting valve makes.

2.4.2   Maintenance

Whenever terminating LCW flow to a device or line, it is important to shut the supply line first then the return line. If the LCW circuit is to be opened, it is important to remember that the closed circuit still has 30-50psi of pressure. The LCW water should be drained in a convenient manner that does not get moisture on any electronics.

When restoring LCW flow to a circuit the return line should be opened first then the supply line. If any connections have been remade they should be carefully inspected for leaks. Major changes to the LCW demands in the hall should be reviewed by Plant Services before implementation.

2.5   Fire

Issues related to fire hazards in Hall B are addressed in a separate document, the "Hall B Fire Assessment Document," CLAS-NOTE 98-007.

There is a map indicating the evacuation routes of the end station complex posted outside the Hall B counting house.

2.6   Mechanical

2.6.1   Crane

Hall B is equipped with a 20 ton polar crane that rotates 360 degrees around the Hall. A space frame with three levels has been erected in the upstream end of Hall B with the uppermost beam having approximately 6" of clearance under the polar crane bridge.

In the center of Hall B a toroid magnet is hung by two support rods attached to beams supported by four columns from the floor. The support posts separating the six cryostats of this magnet are carbon fiber material which would shatter under a lateral collision. Therefore, the area above and inside of the support columns of this magnet is a keep-out zone for the crane hook.

2.6.2   Carriage Movement

During installation and maintenance of the CLAS detector, the carriages that support the calorimeters, scintillators and Cerenkov counters must be moved in and out of their installed positions. Due to the weight of these objects and the precision with which they must be located special care must be taken to insure safe movement. Detailed procedures for these operations are given in Appendix C .