This document will outline the hazards involved with working inside the Alcator C-Mod igloo top. It will also detail the procedures which will be followed to minimize the risk to Plasma Fusion Center workers.
The Alcator C-Mod experiment is surrounded by a concrete ïgloo" which consists of 2¢ thick neutron shielding material. There is sufficient space between the top to the liquid nitrogen dewar and the cap piece of the igloo for a worker to enter. Several diagnostic systems have parts located in this region which must be accessed on occasion.
Leakage of cold nitrogen from the dewar causes a decrease in the percentage of oxygen in the air in this space. Low oxygen is the primary hazard in this area. Introduction of volatile solvents or toxics into this area will create an air quality hazard.
A low energy plasma created by the injection of microwave radiation at 2.45 Ghz into the vacuum vessel is used to prepare vacuum surfaces for full power operation. Leakage of microwave power through windows or feedthroughs on the vertical ports could result in microwave radiation fields in this region. After significant neutron production, ionizing radiation from activated materials could also be present.
This document is designed to provide for safe access to the interior of the Alcator C-Mod igloo top.
Air quality is a primary concern for working inside the Alcator C-Mod igloo top. Leakage of nitrogen from the Alcator C-Mod cryostat could cause depletion of the oxygen available in this area. The air must be monitored for oxygen content. Should solvents be introduced, it should also be monitored for the buildup of flammable or hazardous fumes.
Entry into the space when the electron cyclotron discharge cleaning (ECDC) is operating is discouraged. If it is necessary, however, the area must be surveyed with the appropriate microwave meter to determine that leakage fields do not exceed 1 mW/cm2.
After activation of Alcator C-Mod components has been detected, a radiation survey of the area must be completed prior to manned entry. If dose rates exceed 2 mRem/hour, a radiation work authorization (RWA) must be obtained. All entries must be planned to maintain ionizing radiation exposures as low as is reasonably achievable (ALARA). Appropriate dosimetry must be worn.
Injury could occur from bumping into numerous structures installed inside the experiment.
Confined Space means a space that (1) is lage 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 atmosphere.
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 and 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.
Hot Work Permit means the employer's written authorization to perform operations (for example, riveting, welding, cutting, burning, and heating) capable of providing a source of ignition.
Oxygen deficient atmosphere means an atmosphere containing less than 19.5% oxygen by volume.
Oxygen enriched atmosphere means an atmosphere containing more than 23.5% 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 Entry Supervisor, in addition to the responsibilities ascribed to confined space entrants, is responsible for overseeing the permit entry process. This includes:
The Confined Space Entrant is responsible for:
Confined Space Attendant is responsible for monitoring and protecting confined space entrants. This includes
Personnel allowed access to area underneath the top of the igloo shall be trained in confined space entry and rescue procedures. The project supervisor or the project safety coordinator will oversee this training and approve personnel for entry. A trained confined space attendant must be standing by at any time workers are inside the top of the igloo. A telephone will be available in the Alcator C-Mod cell where this work is being done.
No person will be required to remain underneath the top of the igloo longer than he or she feels comfortable. Personnel working in this area will be required to exit after 4 hours or less.
A confined space permit shall have been obtained.
The space will be ventilated at a rate which will provide 2 air changes per minute (approximately 250 cfm) or as specified by the Industrial Hygiene Office. (It may be necessary to use a smaller blower to prevent a windy feeling). It will be lighted with low voltage lights, with emergency backup 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 top of the igloo 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. Head protection should be worn.
Only personnel who have been trained in entry and rescue techniques will be allowed to enter underneath the igloo top.
Personnel accessing confined spaces and attending confined space entrants must receive basic training in confined space entry.
The following items are added as suggestions or requirements of MIT safety offices or MIT's insurers.
This page maintained by Catherine L. Fiore FIORE@PSFC.MIT.EDU