NMR and MRI Medical Scanners: Surviving the "Invisible Force"

Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body. MRI and nuclear magnetic resonance (NMR) scanners are found in hospitals, nuclear medicine clinics, radiation departments, research facilities and universities across the country. Response personnel must rely on education, signage, on-site visits and knowledgeable facility personnel to understand the hazards posed by MRI and NMR facilities during emergency responses.

In many cases, MRIs give different information about structures in the body than can be seen with an X-ray, ultrasound or computed tomography (CT) scan. MRIs also may show problems that cannot be seen with other imaging methods. NMR uses magnetic fields for research involving radiation and atoms and the identification of structures of organic compounds. While the MRI is used for medical imaging and the NMR is used for research, they have one thing in common – the “invisible force,” a powerful magnetic field that cannot be detected by the human senses.

Signs posted throughout these facilities alert emergency responders to dangerous locations. Primary hazards for responders are magnetic fields and cryogenic liquids used to cool magnets. These magnets can range from 30,000 to 60,000 times greater than the magnetic field of the earth. The fringe magnetic field extending around the scanners creates an environment where ferromagnetic objects become high-speed, potentially fatal projectiles. Metal implants, prostheses and foreign metallic bodies (even those not ferromagnetic) can move or dislodge, causing severe injury.

Firefighter equipment, including but not limited to self-contained breathing apparatus (SCBA), axes and other tools, radios, flashlights, stretchers and defibrillators and any other objects that are ferrous (iron-containing) are not safe to be used around the magnet, nor are metal belt buckles, steel-tipped shoes and any steel protection in firefighter boots. This includes portable fire extinguishers as well. Most facilities have non-ferromagnetic fire extinguishers on site.

Unusual incidents

Accidents have occurred where tools, mop buckets, floor polishers, chairs, acetylene and oxygen tanks and other equipment have been drawn into the magnets during daily operations and during maintenance and repairs. Cell phones, ID cards and credit cards may not work after exposure to a magnetic field.

In 2002, a 6-year-old boy was killed during an MRI scan when a metal oxygen tank was drawn across the room into the scanner by the magnetic force, fracturing his skull and causing brain damage. In 2003, a repairman broke his arm when a piece of metal pinned him to an MRI. He carried the metal into the room and the force of the magnet attracted the metal and the repairman carrying the metal against the MRI machine. Firefighters were called to release him from the machine and treat his injuries.

When responding to an accident where someone has been pinned by a metal object, determine whether the object pinning the victim can be removed without causing further injury. If removal is successful, immediately evacuate the victim to an area outside the magnet room and restrict entry into the magnet room by others. Resuscitation or treatment aided by ferromagnetic devices can be administered once the victim is outside the magnet room.

If a life-threatening emergency exists and there is no way to free the victim without eliminating the magnetic field, then it will be necessary to initiate a magnet “quench” to bring down the magnetic field. The quench procedure will create a dangerous environment. Expect a loud noise from the escape of cryogens and a release of a dense white fog. There is a high risk of asphyxiation and potential for frostbite. As the magnetic field decreases, the object pinning the victim may fall and could cause further damage. Do not perform this procedure unless you are prepared to immediately evacuate yourselves and the victim if oxygen is displaced from the room.

In 2006, two people were injured when an MRI machine they were moving exploded. It is reported that nitrogen and helium still in the machine mixed, causing the explosion. One of the injured had shrapnel in his head and the other an injured arm. Firefighters were called to the facility following the explosion to investigate and treat the injured.

Beware of the force

The power of these magnets should not be underestimated and great care should be exercised by emergency response personnel working near them. All ferromagnetic metals should be removed without exception before entering the facility magnet area. If metal cannot be removed, personnel should not enter.

Magnets at MRI and NMR facilities are always on and there is always a magnetic field present, even if power to the facility or the magnet is disconnected. The only way magnets can be shut down is by quenching. This can occur by instigation through a quench switch located in facility or spontaneous quenching caused by a malfunction in the system. Instigation of a quench using the switch can discharge the magnet in about 20 seconds. Even a partially quenched magnet can pose a hazard and attract ferrous objects such as gas cylinders.

Instigated quenching is the removal of the nitrogen and helium from the magnet and exhausting to the outside of the building. Spontaneous quenching results from a breakdown in the system, which may result in vapors of nitrogen and helium displacing the oxygen in the room and causing simple asphyxiation to anyone not wearing SCBA. When entering an area where oxygen deficiency is suspected or possible, portable oxygen monitoring equipment should be used. During instigated quenching it has also been reported that exhausting equipment has failed resulting in vapors in the room as well.

Quenching cannot only be a dangerous operation, but is very expensive. It can cost over $50,000 to reenergize the magnet and result in a one- to two-month down time. If the magnet needs repair as a result of the quenching, it can cost over $100,000 with several months of down time. If the machine cannot be repaired, replacement can cost more than $2 million. Quenching should only be done under the supervision of facility personnel when there is a life-threatening situation, like a person pinned to the magnet by a large object that cannot be removed by hand or as the result of a large fire so that firefighters can enter the room safely. If an emergency quench is necessary, pressure generated by the quench may prevent doors from opening, so prop open the magnet room door. Allow no others to enter the room through the open door. All personnel must know to leave the room and not return until the cryogenic gases have dissipated and the room is safe to reoccupy.

Ultra-cold materials

In addition to the asphyxiation hazards they present, cryogenic liquid nitrogen and helium are very cold materials and can cause thermal burns and solidification of body parts. Contact with the liquids can solidify personal protective equipment (PPE) normally worn by emergency responders. Avoid contact with the materials. Special gloves are used within the facilities for handling cold or frosted surfaces. These gloves will not provide any protection if submerged in the liquids themselves. Solidification of hands and fingers can occur quickly.

Cryogenic liquids also have large liquid-to-vapor expansion ratios and a small amount of liquid can cause a significant amount of vapor. Helium has a boiling point of 452 degrees below zero. Helium is the only substance on Earth that does not exist as a solid. There is nothing colder to solidify helium. Helium’s expansion ration is 754-1, meaning one gallon of liquid helium would expand to 754 gallons of helium vapor. Nitrogen has a boiling point of 321 degrees below zero and an expansion ratio of 697-1. Extreme caution should be exercised when working in areas where cryogenic liquid or vapor has been released. Both helium and nitrogen gases are odorless and colorless. However, cryogenic gases are so cold they can freeze water vapor in the air, causing a vapor cloud appearance.

Response precautions

Facilities where MRI and NMR are used will be equipped with oxygen monitors and alarms to indicate whether the air is safe to breathe without respiratory protection or if respiratory protection is necessary. If the alarm is sounding, it is likely helium or nitrogen vapors are present and have displaced oxygen in the area. Helium and nitrogen vapors are lighter than air, so crawling on the floor would provide an atmosphere of less helium and nitrogen and more oxygen. Material safety data sheets (MSDS) on helium, nitrogen and any other chemicals in use should be available at the facility.

During firefighting or other emergency operations at an NMR facility, care should be taken to not overturn magnets – they are very top heavy and not very stable. Cryogenic containers called dewars are also top heavy and easily overturned.

In addition to other hazards mentioned above, radiation hazards are present in NMR facilities that may present unique hazards to emergency response personnel. Become familiar with MRI or NMR facilities in your response areas. Consult knowledgeable magnetic resonance personnel, as they are the best source of information when it comes to dealing with the magnetic fields and associated cryogenic hazards.


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ROBERT BURKE, a Firehouse® contributing editor, is a Certified Fire Protection Specialist (CFSP), Fire Inspector II, Fire Inspector III, Fire Investigator and Hazardous Materials Specialist, and has served on state and county hazmat teams. Burke is the author of the textbooks Hazardous Materials Chemistry for Emergency Responders and Counter-Terrorism for Emergency Responders. He can be contacted at robert.burke@windstream.net.