LDX Confined Space Entry


Plasma Science and Fusion Center


Office of Environment, Safety, and Health

190 Albany Street, NW21 2nd floor

617-253-8440 (Catherine Fiore)

617-253-8917 (Matt Fulton)

617-253-5982 (Bill Byford)

617-258-5473 (Nancy Masley)

Fax 617-252-1808


Be Safe or Die






Reviewed and Approved By:



PSFC Supervisor





Catherine L. Fiore, PSFC Safety Officer









Title: Confined Space Operation on LDX


Author: D. Garnier


Version: 1.0


Date: May 21, 2004


Persons Responsible: D. Garnier, J. Kesner, M. Mauel


Other Personnel: See list of approved personnel below.





This document will outline the hazards involved with working inside the LDX vacuum chamber.  It will also detail the procedures which will be followed to minimize the risk to Plasma Science and Fusion Center workers.


The LDX vacuum vessel is a cylindrically shaped structure with internal dimensions of 128" high and diameter of 196". The structure is made of stainless steel (no Inconel is involved).  A cross section is shown in Fig. 1.  The vacuum vessel is accessed via one of four side ports that are 22 in diameter.  An alternate entrance point will be the bottom flange that measures 42 but must be accompanied by scaffolding platform raised to roughly less than 36 from the entrance of the vessel and that will be at least 42 by 42 in platform dimension. Access to the side ports will be available from the mid level platform and with the necessary stepladder to enable easy internal access.  At all times, at least two ports measuring no less than 8 will be open such that a continuous airflow will re-circulate the entire volume (~1200 ft^3) of the chamber at least 40 times per hour.


Work inside the vacuum vessel includes installation of diagnostics, stud welding, chamber cleaning and inspection.


The welding of the studs (which are 3/4" long, 5/16" diameter) is accomplished with a stud-welding gun, which uses up to 200 volts and 20 Amps. The stud is placed in the gun, which is then positioned at the desired location, and the trigger is pulled to weld the stud to the wall. The noise of the discharge is very loud and requires some hearing protection. Once these are welded, the area must be scrubbed clean with ethanol.


Chamber cleaning will be accomplished with acetone and ethanol solvents.  Solvents will be introduced to the space on moistened rags or with a plastic solvent dispensing bottle.   In order to ensure a safe environment, no more than 1 pint of solvent shall be in the chamber at any time.  Also, use of solvents should be limited to 1 pint in any one hour period.
















Figure 1.  Interior of the LDX Vacuum Vessel




This document is designed to provide for safe access to the interior of the LDX vacuum vessel.


Safety Analysis:


Air quality is a primary concern for working inside the LDX vacuum vessel. The air must be monitored for oxygen content and for the buildup of combustible and hazardous fumes. Ethanol will be used for cleaning internal vacuum hardware. Personal oxygen monitors will be provided for those inside the vessel to monitor their oxygen content.


The potential for electrical shock from the welding machinery exists, as well as ultraviolet radiation. The welding could cause spattering from the welding arc and a buildup of welding related fumes (CO, metal oxides.) The stud-welding gun is very loud during the discharge. 


Injury could occur from bumping into structures and studs installed inside the experiment.  Also, when accessing the ceiling of the vacuum space, an aluminum plank will be installed within the chamber.  A fall hazard exists when working on the plank.


Under certain circumstances scaffolding may be used to access space and in such cases, a fall hazard also exists.




Confined space - means a space that (1) is large enough and so configured that an employee can bodily enter and perform assigned work; and (2) has limited or restricted means for entry or exit, and (3) is not designed for continuous employee occupancy.


Entry - means the action by which a person passes through an opening into a permit-required space. Entry includes ensuing work activities in that space and is considered to have occurred as soon as any part of the entrant's body breaks the plane of an opening into the space. Entry permit means the written or printed document that is provided by the employer to allow and control entry into a permit space and that contains the information specified in this document.


Hazardous atmosphere - means an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue, injury, or acute illness from one or more of the following causes: (1) Flammable gas, vapor, or mist in excess of 10% of its lower flammable limit (LFL); (2) Airborne combustible dust at a concentration that meets or exceeds its LFL; (3) Atmospheric oxygen concentration below 19.5 % or above 23.5%; (4) Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in Subpart G, Occupational Health and Environmental Control, or in Subpart Z, Toxic and Hazardous Substances, of this part and which could result in employee exposure in excess of its dose or permissible exposure limit; (5) Any other atmospheric condition that is immediately dangerous to life or health.


Oxygen deficient atmosphere - means an atmosphere containing less than 19.5% oxygen by volume.


Permit-required confined space (permit space) - means a confined space which contains one or more of the following characteristics: (1) Contains, or has a potential to contain a hazardous atmosphere; (2) Contains a material that has the potential for engulfing an entrant; (3) Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section; or (4) Contains any other recognized serious safety or health hazard.




The Assistant Radiation Protection Officer for the PSFC shall determine if the Radiation Work Authorization Procedure (PSFC-RP-91006) and/or the ALARA Procedure (PSFC-RP-91005) need to be implemented.


The Entry Supervisor, in addition to the responsibilities ascribed to confined space entrants, is responsible for overseeing the permit entry process. This includes:


 1.    Preparation and verification of permits. This includes verification that all prescribed tests and procedures have been performed, that all required equipment is available, and that rescue services and a means to summon them are available. This includes radiation work authorizations and ALARA reviews as well as any necessary welding permits.


 2.    Monitoring of the entry to see that conditions and procedures are consistent with the permit.


 3.    Removal of unauthorized persons from the area.


 4.    Termination or cancellation of an entry permit as required.


The Confined Space Entrant is responsible for:


 1.    Understanding the hazards associated with the confined space entry from all sources, which pertain: chemical (from MSDS), reduced O2, electrical, radiation, engulfment, mechanical, etc.


 2.    Proper use of all required equipment.


 3.    Communication with attendant.


 4.    Recognition of requirements for self-rescue, and proceeding with self-rescue when necessary.


 5.    Obeying orders from the attendant and the entry supervisor.


 6.    Complying with all applicable safety procedures established for his/her project, and with the procedures established by the MIT Safety Office and by the MIT Plasma Fusion Center Safety Committee.


The Confined Space Attendant is responsible for monitoring and protecting confined space entrants. This includes:


 1.    Understanding the hazards associated with the confined space entry from all sources which pertain: chemical (from MSDS), reduced O2 , electrical, radiation, engulfment, mechanical, etc.


 2.    Proper use of all required equipment.


 3.    Communication with the entrant.


 4.    Recognition of requirements for self-rescue, and ordering the entrant to proceed with self-rescue when necessary.


 5.    Ordering evacuation if an uncontrolled hazard is detected, if the entrant exhibits behavioral effects of hazardous material exposure, if predetermined entry times are exceeded, if a situation develops outside the space, which could endanger entrants, or the attendant can no longer perform his/her duties.


 6.    Summoning rescue personnel as required.


 7.    Following instructions of the entry supervisor.




Personnel allowed access to the vacuum vessel would be trained in confined space entry and rescue procedures on the vacuum vessel. The project supervisor will oversee this training and approve personnel for entry. A person capable of accessing the vessel must be standing by at any time workers are inside the vacuum vessel. A telephone will be available in the LDX cell where this work is being done. No more than 4 people will ever be allowed inside the vessel simultaneously.


All personnel approved to enter the vacuum vessel will be trained in rescue procedures. At least one person approved for access will be standing by at any time there is a worker inside the vacuum vessel. This person must maintain frequent verbal communications and, when possible, visual contact with the worker inside the vessel.


No person will be required to remain inside the vessel longer than he or she feels comfortable. Personnel working inside the vessel will be required to exit after 4 hours or less.


All required permits, e.g., confined space entry, radiation work authorization, or welding permits have been obtained. All special equipment and protective clothing required by these permits have been obtained.


All external hazards, e.g., ECRH, magnet currents, glow discharge electrodes, gas puffing system, have been locked out.


Required Equipment:


The space will be ventilated at a rate, which will provide 40 air changes per hour (approximately 900 cfm) or as specified by the Industrial Hygiene Office. It will be lighted with low voltage lights.  The attendant will be equipped with a flashlight in the event of a power failure. Continuous oxygen and flammable gas monitoring will be done at all times that the space is occupied.


Those working inside the vacuum vessel will wear protective clothing appropriate to the tasks, which they are performing. Welding operations will require the wearing of leather gloves, protective eyewear, etc. Use of the stud-welding gun will require ear protection.  Flame retardant suits should be worn during welding instead of Tyvek, which burns too easily.




Only personnel who have had confined space training and have been trained in entry and rescue techniques will be allowed to enter the vacuum vessel. A list of the approved persons will be posted at the site.


 1.    The ventilation system must be set up on the vacuum vessel and be operating before entry is attempted.


 2.    An oxygen and flammable gas monitor will be inserted into the vessel and checked before entry is attempted. This monitor must be operating at all times that personnel are inside the vacuum vessel. Anyone working inside the vessel must exit immediately if an alarm is registered on this meter. No one may enter this space if an alarm is registered. A maintenance schedule for this meter is attached to this procedure.


 3.    Low voltage lighting must be inserted into the vessel, or fluorescent port lighting fixtures must be turned on before entry is attempted.


 4.    A second person approved for entry into the vacuum vessel (confined space attendant) must be standing by. This person must maintain frequent verbal communications and, when possible, visual contact with the worker inside the vessel. An additional person, capable of assisting with the removal of a worker from the vessel from outside of the vessel must be in the area as well.


 5.    Materials to be taken inside the vessel must be reviewed for toxicity by the Industrial Hygiene Office. Any precautions specified by IHO must be observed. Vacuum protective clothing must be non-flammable for welding and spot welding applications.


 6.    The set up of any welding operations inside the vessel must be reviewed by the welding supervisor and approved for safety. The workers welding inside the machine must wear the appropriate clothing and protective gear.


 7.    A fire extinguisher must be available on the deck. The fire extinguisher on the scaffolding shall consist of one of the following three items: A water hose with spray nozzle; A bicarbonate of soda dry chemical fire extinguisher; or several fire blankets. The water or dry chemical extinguisher is preferred.


 8.    An audible alarm must be available for emergencies. The fire pull alarms in the cell are deemed acceptable for this purpose. In an emergency situation, the rescuers should pull one of the fire alarm switches.


  9.    Any person entering must be familiar with these procedures. That person should verify for his or herself that the oxygen-flammable gas monitor is installed, that the lighting is provided from a low voltage source, that the blower is operating, that the fire extinguisher is at hand, and that approved spotters are standing by.


10.    These procedures must be posted at the site.


In addition the entry supervisor shall:


 1.    Check the entry procedure and make sure that all of the required equipment has been assembled.


 2.    Make sure that any ventilating equipment has been installed and is operating satisfactorily.


 3.    Check that all required measurements of atmosphere have been performed and that levels are in a satisfactory range.


 4.    Satisfy him/herself that the attendants and entrants understand their responsibilities and the procedure to be followed.


 5.    Fill out the permit (blanks should be obtained from the ES&H office) and post it at the entry site.


 6.    At completion of the entry the entry supervisor shall return the permit to the ES&H office.




       The supervisor must observe this training and verify that the worker is capable of performing simple rescue techniques. The supervisor must also verify that the worker is capable of entering and exiting the vessel under his or her own power.


       Personnel allowed access to the vacuum vessel would be trained in confined space entry and rescue procedures on the vacuum vessel. The project supervisor will oversee this training and approve personnel for entry.