Transcription

NON-IONIZINGRADIATION (NIR)SAFETY MANUAL

CONTENTSIntroduction to NIRRegulatory RequirementsThe Electromagnetic SpectrumStatic Magnetic FieldsMagnetic FieldsApplicationsHazardsSafety StandardsResponsibilitiesSuperconducting Magnets: Additional InformationSafe Handling of Cryogenic SubstancesRefill of Liquid HeliumRefill of Liquid NitrogenVentilationScreening form: Large Magnetic SourcesELF (Extremely Low Frequency)Electric FieldsApplicationsHazardsSafety StandardsResponsibilitiesMicrowave/RF FrequencyRF and MWApplicationsHazardsSafety StandardsResponsibilitiesNon-laser Light SourcesInfrared (IR) and Visible LightInfraredVisible LightApplicationsHazardsSafety StandardsResponsibilitiesUV HazardsUltraviolet (UV) LightApplicationsHazardsSafety StandardsResponsibilitiesUV Light: Frequently Asked Questions (FAQs)EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 2 of 45

INTRODUCTION TO NIRRegulatory RequirementsIn addition to its ionizing radiation safety program, the University of Washington (UW) responds toa wide range of non-ionizing radiation (NIR) concerns. In recent years there has been an increasein devices that use or emit non-ionizing radiation. Questions about acute or chronic effects havesubsequently become more important.The UW Environmental Health & Safety Department’s (EH&S’s) Radiation Safety team, therefore,has the role of providing safety information and monitoring exposure to operators of NIRequipment in order to reduce risk of injury and prevent overexposure. This guide is designed toprovide information about such hazards. The UW enforces all national protection standardsrelevant to each range of hazard, in particular the Threshold Limit Values (TLVs ) and BiologicalExposure Indices (BEIs ) of the ACGIH (American Conference of Governmental IndustrialHygienists).The Electromagnetic SpectrumLike ionizing radiation, such as x-rays and gamma rays, NIR is a part of the electromagnetic (EM)spectrum and is propagated as waves through a vacuum or some medium. However, NIR differsfrom ionizing radiation because it consists of lower quantum energies and, therefore, has differentbiological effects. NIR displays its own unique personality.Since NIR shares the same wave characteristics as ionizing radiation it can be described in termsof its wavelength, frequency, and energy. Though compared to its ionizing sibling, NIR is longer,less frequent, and lazier. It can still, though, inflict a good deal of damage.NIR is most often described as being bound by the following characteristics:EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 3 of 45

NIR CHARACTERISTICSWavelengths:Frequencies:100 nm to 300,000 km3.0 PHz to 1 HzPhoton energy: 1.987 x 10-18 J to 6.6 x 10-34 JEach characteristic (wavelength, frequency, and energy) will be discussed below.Basic Wave ConceptElectromagnetic radiation is the propagation of energy. This energy consists of oscillating electricand magnetic fields, which are transverse and perpendicular to each other. An electromagneticwave is essentially then made up of fields which are inter-related and interdependent. Both fieldscan exert a force. An electric field can affect an electric charge (for example, an electron). And amagnetic field can, in turn, affect a moving charge (current).Electromagnetic theory as developed by Maxwell and others describes a magnetic field that variesin time and that induces a perpendicular electric field. The changing electric field, likewise, inducesa perpendicular magnetic field. The two fields in essence produce each other and propagatetogether. The different regions of the EM spectrum have different properties but they are allpropagated at the same speed in a vacuum: 3 x 108 m per second, known as the speed of light,usually designated as c. The velocity of the EM wave in a medium, however, is determined by theelectric and magnetic properties of that medium.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 4 of 45

The image of a wave, of course, is a simplified representation of the EM spectrum. Electromagneticwaves are not simply waves, but have a dual nature. They can be described has having a waveaction with wave effects, but under some circumstances, especially at higher energies, they canbehave as a bundle of waves (a photon) and can interact with matter as a particle would.Wavelength (λ)The names of the different EM regions essentially refer to the methods of wave generation ordetection. There is no sharp distinction between the regions, though customarily they have beendefined as having the following dimensions:RegionionizingGamma and aveRadiofrequencyλ 1 nm (10-9 m)1 - 400 nm400 -700 nm700 - 1,000,000 nm (1 millimeter)1 mm - 1 m1 m – 100 kmThe range for NIR is quite large, from 100 nanometers in the ultraviolet to over 300,000 km in theradiofrequency region. Each range of wavelengths is absorbed differently by the human body,resulting in different biological effects.FrequencyEH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 5 of 45

The number of waves that pass a fixed point during an interval of time is referred to as the wavefrequency (f or the Greek letter ν). Frequency is measured by counting the number of wavesthat pass a fixed point in one second. From one wave crest to another is called a cycle, sofrequency is often described as cycles per second (or Hertz). One wave, or cycle, per secondwould therefore have a frequency of 1 Hertz (Hz).Since EM waves travel at the speed of light (in a vacuum), if the wavelength of any wave is given,then the frequency can be derived, and vice versa:f c/λExample: The frequency of a given wave is 7.5 x 1014 Hz. What would be thewavelength?Answer:f c/λ7.5 x 1014 Hz 3 x 108 m/secλλ 3 x 108 m/sec 4 x 10-7 m or 400 nm7.5 x 1014 HzA wavelength of 400 nm would place this wave in the visible region of the EM spectrum and wouldbe interpreted by us as being violet.EnergyUnlike ionizing radiation, NIR does not have energy levels high enough to ionize a molecule, thatis, eject an electron. Usually a photon energy near 1.987 x 10-18 J (12.4eV) is needed to ionizeatoms.Gamma and x-rays, as well as UV radiation near a 100 nm wavelength, have sufficient energy toionize molecules and are, therefore, considered to be ionizing radiation. In general, the UV portionof the spectrum is not included in the ionizing region because UV at wavelengths less than 295 nmare filtered by the atmosphere. UV at these short wavelengths, however, can be produced in sometypes of lasers, so would, under these circumstances, be considered ionizing.The energy of any given wave on the EM spectrum is proportional to its frequency, described inthe equation:E hfwhere h is Planck’s constant (6.63 x 10-34 J/sec).EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 6 of 45

Example: If we measure a band of light and find that its photon energy is 0.1 eV, what would bethe wavelength of this light? What would be its color?Answer:E hf hcλλ hcEλ (6.6 x 10-34 J/sec) (3 x 1010 cm/sec)(0.1 eV) (1.6 x 10-19 J)λ 1.24 x 10-3 cm 12.4 μmThis would place the measured light in the infrared region of the spectrum.In this guide each region of the EM spectrum that is defined as non-ionizing will be examined interms of hazards as well as levels of safety responsibility.STATIC MAGNETIC FIELDSMagnetic FieldsMagnetic fields are associated with magnets. Magnetic fields of force are created by the motion ofa magnet’s electrons and the alignment of its atoms. The greater the magnetic flux density of amagnet, the greater the chance for potential hazard. Magnetic fields are generally measured ineither Gauss (G) or Tesla (T).10,000 Gauss 1 Tesla (T)1 Gauss 0.1 mT 100 μT.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 7 of 45

Magnetic fields can surround any electrical device when there is a flow of current. The magneticfield increases in strength as the electric current increases.ApplicationsMost sources of static magnetic fields at the University are either an MRI (Magnetic ResonanceImaging) unit or an NMR (Nuclear Magnetic Resonance) system. There are also several largemagnets used for instructional purposes.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 8 of 45

HazardsSeveral reviews of laboratory and epidemiological research have been conducted by national andinternational organizations. None of the reviews has found a correlation between health hazardsand static magnetic fields encountered in residential and occupational environments. There is nodirect evidence that such fields are mutagenic or carcinogenic, nor are they likely to causedevelopmental abnormalities or chronic effects below an exposure of 20,000 G. Some of theconclusions of these reviewing organizations are provided below:American Conference of Governmental Industrial Hygienists (ACGIH), 1993, concludedthat:“no specific target organs for deleterious magnetic field effects can be identified at thepresent time Although some effects (of static magnetic fields) have been observed in bothhumans and animals, there have not been any clearly deleterious effects conclusivelydemonstrated at magnetic field levels up to 2T (2000 mT).”2T 20,000 GInternational Commission on Non-Ionizing Radiation Protection (ICNIRP), 1994,concluded that:“current scientific knowledge does not suggest any detrimental effect on majordevelopmental, behavioral and physiological parameters in higher organisms for transient exposureto static field densities up to 2 T (2000 mT). From analysis of the established interactions, longterm exposure to magnetic flux densities of 200 mT should not have adverse consequences.”Although there is no direct evidence of health hazards, there are indirect effects, such as flyingferromagnetic objects which can cause injury. Sometimes magnetic interference can occur withcardiac pacemakers and other precision electronic equipment. Safety standards, therefore, shouldEH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 9 of 45

be followed by individuals and patients who may enter areas of large magnetic fields, such as inthe vicinity of MRI machines.Effects and LevelsCompass may be deflected0.1 GEarth’s magnetic field0.5 GPrecision instruments or TVmonitor colors may be affected1.0 GCardiac pacemakers and other implantedelectronic devices may be affected5.0 GCredit cards, magnetic storage systems,and analog watches may be damaged10.0 GFerromagnetic objects can become projectiles10.0 GCathode-ray devices and tubes may malfunction20.0 GField around small permanent magnets andAudio-speaker magnets at 1 cm from poles10 to 100 GMagnetic Resonance Imaging (MRI)1,500 to 20,000 GDue to the possible effect on older pacem akers, ow ners of large m agnets should havevisible m arkers as to w here the m agnetic field is 5.0 Gauss.Related EffectsIn addition to the effects of a magnetic field there are hazards not directly associated with themagnet itself but can pose a safety hazard. Essentially they fall into two categories: electrical andquench effects.Electrical HazardsSome electrically conductive materials (non-magnetic) can form resistance due to induced eddycurrents. Electrical supply circuits and magnetic cores should be grounded to prevent voltages,induced by eddy currents, from building up.Another concern can be exposed leads. If a metal tool, for example, should come in contact withan exposed lead it could result in an electrical short, which can then form an arc flash and possiblyvaporize the tool. More importantly, if the terminal voltages exceed 50V and if the inductive energyis greater than 0.5J (due to the loss of conductor continuity), the result can be theelectrocution of anyone w ho touches an exposed, energized lead.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 10 of 45

Quench HazardsWith superconducting magnets there is the chance of a sudden discharge of magnetic field energy,which can cause serious injury to personnel (via electrical shock or burns) or damage toequipment. This sudden discharge is known as quench. Eddy currents can form, as well as a greatdeal of heat. If a superconducting magnet does quench, in addition to the electrical energy andheat discharge, there can be a sudden venting of boiled-off cryogens, leading to cryo-burns.When quenching occurs there will also be an unexpected loud noise which may startle personneland cause other injuries.Safety StandardsThe University enforces the ACGIH (2004) standard with regards to static magnetic sourcesafety. The recommended limits are as follows:ACGIH (2004)Occupational Continuous Exposure(whole body)600 GOccupational Extremity Exposure6,000 GCeiling Exposure (whole body)Ceiling Exposure (extremity)20,000 G50,000 GThe above levels are for routine occupational exposures on a daily, 8-hour-time-weighted basis.Persons with the following conditions are NOT eligible for MRI scanning:Aneurysm vascular clips, intracranial bypass graft clips, eye orbital prostheses (metal shankanchors), metal middle and inner ear prosthesis, cardiac pacemakers, recent post operativecases with metal clips or wire implants, and some types of implanted therapeutic deviceswith metal (such as insulin pumps). Individuals with bullet or shrapnel fragments must haveeligibility evaluated by a physician. Individuals with certain metal implants are eligible forscanning, such as tantalum mesh plates and gold or amalgam fillings in teeth.ResponsibilitiesRadiation SafetyThe RSO will provide training when requested by the Department, supervisor, or individual.Upon request, Radiation Safety can monitor an area for potential hazards and providerecommendations.DepartmentThe Department will notify Radiation Safety when magnetic equipment is scheduled to bepurchased or transferred.SupervisorThe supervisor will ensure that all appropriate signage is posted and that the 5 Gauss line isclearly indicated.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 11 of 45

Will make sure that all personnel or visitors entering the magnetic field area are qualified todo so and that they understand the potential hazards.PersonnelIndividuals will obtain authorization to enter a designated static magnetic field area from themagnet supervisor or department.Individuals will also check and comply with all posted requirements.If an individual does not feel qualified or sufficiently trained to perform a specific task in amagnetic area or feels that there is a health condition that could be affected by a magneticfield, he/she should notify the supervisor or Radiation Safety.Individuals will remove all ferromagnetic tools, jewelry, and other objects from a field thatcould pose a ferromagnetic hazard ( 10 G).Superconducting Magnets: Additional InformationWith Nuclear Magnetic Resonance (NMR), Magnetic Resonance Imaging (MRI), andother superconducting magnetic equipment there are a number of unique safety concerns.Radiation Safety is responsible for determining specific hazards for each facility housing suchmagnetic sources, identifying hazardous areas, reviewing safety precautions, and providingtraining when needed.Supervisors and principal investigators are responsible for ensuring that all personnel are trained toperform safely the tasks assigned to them and that all protective control measures are maintained.Non-user staff such as administrators and custodians should also be trained not to enter themagnet room. Supervisors are responsible for ensuring that work done, in the vicinity of highmagnetic fields, by facilities personnel or contractors will be carried out appropriately and safely.All contract work should be reviewed for safety concerns prior to scheduling.Magnetic Field Hazards Ferromagnetic objects shall be kept outside a pre-determined radius in order to preventthose objects from becoming projectiles, which can cause severe injury to personnel aswell as equipment damage. Examples of such ferromagnetic objects are fireextinguishers, tools, radios, wheelchairs, keys, defibrillators, jewelry, hearing aids,magnetic stirring bars, watches, scissors, badges, flashlights, etc. If the magnetic field is 100 gauss or greater, gauss lines of 100, 10, and 5 gauss shouldbe clearly indicated. No work stations should be within the 5 gauss line, nor should theline intrude into public thoroughfares, nor entrances or exit spaces. This also includeslocations above and below the magnet room. All gas cylinders shall be secured. If used within the 100 gauss line, all tools should benon-magnetic. Magnetic objects in general should be secured or kept outside the 100gauss line.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 12 of 45

Magnetically-sensitive equipment, such as implants and cardiac pacemakers, can beadversely affected, resulting in injury or death. All individuals with pacemakers arerestricted to areas that have a magnetic field of less than 5 gauss. Metallic implants (even if not ferromagnetic) can move in a magnetic field and in somecases become dislodged. In cases of a rapidly changing field, eddy currents couldpossibly be induced in an implant, resulting in a serious heating of the implant.Examples of such implants include pins, shrapnel, insulin pumps, aneurysm clips,cochlear implants, and prosthetic limbs. All magnetic storage media, especially credit cards, can be destroyed by magneticfields. Credit and ATM cards should be kept beyond the 10 gauss line. Room size should be considered when installing an NMR. During a quench event nearlyhalf of the helium volume will boil off very rapidly and form a white vapor above themagnet. Once a quench begins (boil off of cryogens when the magnetic field is lost) itwill not stop until all the helium boils off. The result is a very large and expanding vaporcloud. The room must be large enough to accommodate the initial cloud. Exhaustventilation must be adequate for the room under quench event conditions. If room size or ventilation is inadequate, then helium vent pipes should be installed tothe quench valve, or oxygen monitor-connected exhaust fans should be used.Cryogen Hazards Both liquid helium and liquid nitrogen are colorless and odorless. If a sudden magneticquench occurs then these gases can now displace oxygen in the magnet room, causingasphyxiation. Oxygen sensor alarms should be installed. Liquid helium is at – 452 F and liquid nitrogen is at – 320 F. The liquid itself or itsvapors can cause severe frostbite. During cryogen filling operations personnel shall use at least thermal gloves, faceshields, lab coats, long pants, and covered shoes. Proper procedures for filling andtransport should always be followed. At least two staff members should be presentduring filling. Quench prevention is paramount. Training of personnel should include quenchprevention and emergency procedures, including evacuation.Fire Hazards Magnetic systems fire can cause the magnet to dangerously rupture. If a magnetic quench occurs the extreme cold of the gases may cause the air tocondense on surfaces. The moisture on these surfaces is most likely liquid oxygen andwould be a potential fire hazard.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 13 of 45

At minimum, one fire extinguisher (that is magnetically compatible) should be availablejust outside the magnet room.Other Hazards Caution should be taken around high energy power supplies to prevent accidentalcontact. Every attempt should be made to keep power cords and cables off the floorand reduce tripping hazards. Evacuation routes should be clearly visible. Unescortedvisitors should never be allowed in the area of high magnetic fields. Electrical transformers could be magnetically saturated above 50 gauss. If flooding occurs there could be the risk of electrocution.Signage The appropriate signage shall be posted at all entrances to the magnet room indicatingthe hazards and prohibiting unauthorized personnel in the area.Emergency Procedures Emergency procedures are specific for each facility and should be organized with theassistance of Radiation Safety and posted.Magnetic Field Units and Conversion Factors Magnetic Fields are generally measured in tesla (T) or millitesla (mT). In the US, fieldsare often measured in gauss (G) or milligauss (mG):1T 1,000 mT1G 1,000 mG1T 10,000G1mT 10,000mGSafe Handling of Cryogenic SubstancesA superconducting magnet uses two types of cryogens, liquid helium and liquid nitrogen.Cryogenic liquids can be handled easily and safely provided certain precautions are obeyed. Therecommendations in this section are by no means exhaustive, and when in doubt the user isadvised to consult the supplier.Types of substances: The substances referred to in these recommendations are nitrogen, heliumand air. Contact your cryogen supplier or EHS for the appropriate MSDS sheets for these cryogens. Helium: This is a naturally occurring, inert gas that becomes a liquid at approximately4K. It is colorless, odorless, non-flammable and non-toxic. In order to remain in asuperconducting state the magnet is immersed in a bath of liquid helium.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 14 of 45

Nitrogen: This is a naturally occurring gas that becomes liquid at approximately 77K. Itis also colorless, odorless, non-flammable and non-toxic. It is used to cool the shields,which surround the liquid helium reservoir.Cryogen transport Dewars: During normal operation, liquid cryogens evaporate and will requirereplenishment on a regular basis. The cryogens will be delivered to site in transport Dewars. It isessential that these cryogen transport Dew ars are non-m agnetic.Physical properties: Safe handling of cryogenic liquids requires some knowledge of the physicalproperties of these liquids, common sense and sufficient understanding to predict the reactions ofsuch liquids under certain physical conditions.General Safety RulesGeneral safety rules for handling cryogenic substances include, but are not limited to: Cryogenic liquids remain at a constant temperature by their respective boiling pointsand will gradually evaporate, even when kept in insulated storage vessels (Dewars). Cryogenic liquids must be handled and stored in well ventilated areas. Passengers should never accompany cryogens in an elevator. There is a risk ofasphyxiation. The very large increase in volume accompanying the vaporization of the liquid intogas and the subsequent process of warming up is approximately 740:1 for heliumand 680:1 for nitrogen.Cryogen Transport DewarsThe rules concerning the cryogen Dewars used to transport cryogenic liquids include, but are notlimited to: All cryogen Dewars transporting cryogenic liquids must not be closed completely as thiswould result in a large buildup of pressure. This w ill present an explosion hazard andm ay lead to large product losses! All cryogen transport Dewars must be constructed of non-magnetic materials.Health HazardsMain health hazard related rules include, but are not limited to: Evacuate the area immediately in the event of a large spillage. Provide adequate ventilation in the room to avoid oxygen depletion. Helium can displace airin the upper area of a room and cold nitrogen can displace air in the lower area. Please seethe “Ventilation” section for detailed information.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 15 of 45

Do not come in direct contact with cryogenic substances in liquid or vapor form (or as lowtemperature gases), since they will produce “cold burns” on the skin similar to burns. Do not allow insufficiently protected parts of the body to come in contact with noninsulated venting pipes or vessels (see “Ventilation” section), since the body parts willimmediately stick to them. This will cause the flesh be torn if the affected body part isremoved.First AidFirst aid rules include, but are not limited to: If any of the cryogenic liquids come into contact with eyes or skin, immediatelyflood the affected area with large quantities of cold or tepid water and then applycold compresses. Never use hot water or dry heat. Medical advice should be sought immediately!Protective ClothingProtective clothing rules include, but are not limited to: Protective clothing must be worn mainly to avoid cold burns. Therefore dry leather orcryogenic gloves must be worn when handling or working with cryogenic liquids. Gloves must be loose fitting so that they can be removed easily in case of liquid spillage. Goggles must be worn to protect the eyes. Any metallic objects (e.g. jewelry) should not be worn on those parts of the body whichmay come into contact with the liquid.OthersOther rules of handling cryogens include, but are not limited to: Handle the liquids carefully at all times. Boiling and splashing will always occur when fillinga warm container. Beware of liquid splashing and rapid flash off of cryogens when immersing equipment atambient temperature into the liquid cryogens. This operation must be carried out veryslowly. When inserting open ended pipes into the liquid, never allow open ended pipes to pointdirectly towards any person.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 16 of 45

Use only metal or Teflon tubing connected by flexible metal or Teflon hose fortransferring liquid nitrogen. Use only gum rubber or Teflon tubing. Do not use Tygon or plastic tubing. They may split or shatter when cooled by the liquidflowing through it and could cause injury to personnel.SmokingPlease obey the following basic rules concerning smoking: Do not smoke in any rooms in which cryogenic liquids are being handled. Designate all rooms in which cryogenic liquids are being handled as “No Smoking” areas,using appropriate signsAdditional facts and precautions While nitrogen and helium do not support combustion, their extreme cold Dewar causesoxygen from the air to condense on the Dewar surfaces, which may increase the oxygenconcentration locally. There is a particular fire danger if the cold surfaces are covered with oil or grease, whichare combustible. Self-ignition could occur!DewarEH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 17 of 45

PropertiesNitrogenHeliumMolecular weight284Normal boiling point ( C)( K)-19677-2694.2Approximate expansionratio: volume of gas a 15 Cand atmospheric pressureproduced by unit volume ofliquid at normal boiling point680:1740:1Density of liquid at normalboiling point (kg m-3)810125Color (liquid)NoneNoneColor (gas)NoneNoneOdor (gas)NoneNoneToxicityVery lowVery lowExplosion hazard withcombustible materialNoNoPressure rupture if liquid orcold gas is trappedYesYesFire hazard: combustibleNoNoFire hazard: promotesignition directlyNoNoFire hazard: liquefies oxygenand promotes ignitionNoNoEH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 18 of 45

Refill of Liquid HeliumR ead This First!Please read this carefully and make it accessible to anybody working with the magnetsystem.A shielded superconducting NMR Magnet System can be operated easily and safely providedthe correct procedures are obeyed and certain precautions observed.The recommendations in this section cannot cover every eventuality and if any doubt arisesduring the operation of the system, the user is strongly advised to contact the supplier.General Rules When Handling Liquid HeliumBe aware of these general rules including, but not limited to: Liquid helium is the coldest of all cryogenic liquids. Liquid helium will condense and solidify any other gas (air) coming into contact withit. Liquid helium must be kept in specially designed storage or transport Dewars. Dewars should have a one way valve fitted on the helium neck at all times, in orderto avoid air entering the neck and plugging it with ice. Only vacuum insulated pipes should be used for liquid helium transfer. Breakdown ofthe insulation may give rise to the condensation of oxygen.The Helium VesselThe superconducting NMR magnets contain an inner vessel with liquid helium. The helium vessel should be checked weekly for boil-off and helium level. Use a helium flow meter or a helium gas counter! A one way valve is supplied to be mounted on the helium manifold to ensure that thehelium neck tubes cannot be locked by the ingress of air or moisture. This valveshould be mounted at all times except during a helium transfer.Refill of Liquid HeliumPlease follow the following instructions concerning the refill of NMR magnets with liquidhelium: Refill the helium vessel within the specified hold time period and certainly before thelevel falls below the allowed m inim um level listed in the magnet manual.EH&S Radiation Safety Non-ionizing Radiation Safety Manual June 2017Page 19 of 45

Important Note: Transfer of liquid helium can be done easily and safely,provided: The handling of the helium transfer line is correct, The helium transfer line is not damaged, and The transfer pressure does not exceed 2 psi.Never insert a warm helium transfer line into the cryostat, since the warm helium gas couldlead to a quench of the magnet!Always allow the helium transfer line to cool down to helium temperature before inserting itinto the right helium neck tube. You should see liquid helium leaving of the short endtransfer lines for a few moments, before inserting it into the right helium neck tube.Rapid Helium TransferDo not rem ove the nitrogen security flow system during any transfer liquidhelium !During a rapid transfer of liquid helium, super cooling of the liquid nitrogen occurs. This canlead to the following: Decrease of static boil off to zero, and produ

Electromagnetic theory as developed by Maxwell and others describes a magnetic field that varies in time and that induces a perpendicular electric field.