5.
OPERATIONAL REQUIREMENTS
5.1
Training of Cryogenic Personnel
All personnel working with cryogenic fluids must be thoroughly
familiar with the hazards involved. They must also be familiar with all
emergency measures that might be required in the event of an accident.
Employees who have not worked with cryogenic fluids and systems must be trained
on the job by experienced employees until thoroughly familiar with safe methods
of operation.
The training will address:
● The
physical, chemical and physiological hazards associated with cryogenic fluids
● The
proper handling procedures for cryogens and cryogenic containers
● The
emergency procedures required in case of an accident
● The
reporting procedures in case of an accident
Additionally, each employee will receive training by the
responsible scientist on the specific cryogenic equipment or system he is
expected to use. This will cover:
● Description
of the equipment
● Operating
procedures
● Maintenance
schedule and procedures
● Specific
hazards
● Reporting
of incidents
The training shall be documented. The documentation
shall include: 1) content of training, 2) date, 3) name of trainer, 4) a
dated training attendance list showing names of the trainees (typed or printed)
and their signatures.
5.1.1 Cryogen Handling
The hazards associated with the handling of cryogenic fluids
include:
● Cold
contact burns and freezing (contact with cold liquid, gas or surface)
The
potential for freezing by contact with the extreme cold of cryogens
necessitates varying degrees of eye, hand and body protection. When a
cryogenic fluid is spilled on a person, a thin gaseous layer apparently forms
next to the skin. This layer protects tissue from freezing, provided the
contact with the cryogen involves small quantities of liquid and brief
exposures to dry skin. However, having moist skin, exposure to moving
cryogens, or extended periods of time, can freeze tissue.
The
most likely cause of frostbite to the hands and body is contact with cold metal
surfaces. Since there is no protective layer of gas formed, frostbite
will occur almost instantaneously, especially when the skin is moist.
The
damage from this freezing (frostbite) occurs as the tissue thaws. Intense
hypothermia (abnormal accumulation of blood) usually takes place.
Additionally, a blood clot may form along with the accumulation of body fluids,
which decreases the local circulation of blood.
Adequate
protection and clothing is required at all times when handling, transferring or
operating near cryogenic fluids (see 5.1.2).
● Asphyxiation
(displacement of oxygen by inert gas)
When
liquid cryogens are expelled into the atmosphere at room temperature, they
evaporate and expand on the order of 700 to 800 times their liquid
volume. Even small amounts of liquid can displace large amounts of oxygen
gas and decrease the oxygen content of the atmosphere below a safe level with a
possibility of asphyxiation.
Whenever
possible, handling of cryogenic fluids where release into the atmosphere is
possible should be done in open, well ventilated areas.
When
there is the possibility of an oxygen deficiency hazard (ODH) with a level of
risk greater than Class 0, (see Appendix 3) oxygen monitors will be
installed. If such a monitor triggers an ODH alarm, personnel are to
leave the area immediately.
● Explosion
(excessive buildup of pressure in container of cryogenic fluid)
Heat
flux into the cryogen is unavoidable regardless of the quality of the
insulation provided. Since cryogenic fluids have small latent heats and
expand 700 to 800 times to room temperature, even a small heat input can create
large pressure increases.
Dewars
must be moved carefully. Sloshing liquid into warmer regions of the
container can cause sharp pressure rises.
Pressure
relief devices must be provided on each and every part of a cryogenic
system. Satisfactory operation of these devices must be checked
periodically and may not be defeated or modified at any time.
Vents
must be protected against icing and plugging. When all vents are closed,
enough gas can boil off in a short time to cause an explosion. Vents must
be maintained open at all times.
Liquid
helium is cold enough to solidify atmospheric air. Only helium should be
introduced or allowed to enter the helium volume of a liquid helium
dewar. Precautions should be taken to prevent air from back-diffusing
into the helium volume.
Some
materials may become brittle at low temperature and fail in the case of
overpressure or mechanical shock. Only suitable materials may be used to
store or transfer liquid cryogens.
● Fire/explosion
(condensation of liquid oxygen)
Liquid
oxygen liquifies at a higher temperature than liquid helium or nitrogen.
Consequently, liquid oxygen can condense on the exterior of cryogenic
containers or transfer lines. An explosive situation may result if this
oxygen-rich liquid is allowed to soak insulating or other materials which are
not compatible with oxygen.
Some
oils can form an explosive mixture when combined with liquid oxygen.
Surfaces where there exists a possibility of liquid oxygen condensation must be
thoroughly cleaned and degreased.
5.1.2 Protective
Clothing
Whenever handling or transfer of cryogenic fluids might
result in exposure to the cold liquid, boil-off gas, or surface, protective
clothing shall be worn. This will include:
● face
shield or safety goggles
● safety
gloves
● long-sleeved
shirts, lab coats, aprons.
Eye protection is required at all times when working with
cryogenic fluids. When pouring a cryogen, working with a wide mouth dewar
or around the exhaust of cold boil-off gas, use of a full face shield is
recommended.
Hand protection is required to guard against the hazard of
touching cold surfaces. Loose insulating gloves can be used.
5.2 Maintenance and Inspection
Cryogenic systems and equipment must be inspected and
maintained on a regular basis by qualified personnel to ensure safety.
The schedule and nature of the maintenance must be included in the operating
procedures manual. The inspection and maintenance shall be documented.
Every cryogenic system or equipment shall be inspected by
qualified personnel before being put into operation for the first time or after
modification. Inspection by qualified personnel shall also take place
after an unusual incident which might affect the integrity and safety of a
piece of cryogenic equipment.
One should note that these requirements for inspection,
maintenance, calibration and documentation extend to the monitoring systems for
oxygen deficiency.
5.3 Lockout-Tagout Procedure
The Lockout/Tagout Policy establishes basic requirements
involved in locking and/or tagging out equipment while installation,
maintenance, testing, repair or construction operations are in progress.
The primary purpose is to prevent hazardous exposure to personnel and possible
equipment damage. The procedures shall apply to the shutdown of all
potential energy sources associated with the equipment. These could
include pressures, flows of fluids and gases, electrical power, and radiation.
The formal lockout/tagout procedure for the Physics Division
has been written and is the responsibility of the Physics Division Electrical
Safety Committee. It is included as Appendix A of the Physics Division
Electrical Safety Policy and Manual. The ANL-E lockout/tagout policy and
procedure is included in the ESH Manual. The Physics Division procedure
conforms to the ANL-E policy and procedure.
All personnel who are involved in the installation,
maintenance, testing repair, or construction of cryogenic equipment in which
there are energy sources associated with the equipment must undergo documented
training in the use of the Physics Lockout/Tagout procedure.
5.4 Emergency Procedures
In case of emergency, e.g. explosion of a dewar, leave the
area immediately and dial 911.