How to Safely Operate a Nuclear Magnetic Resonance (NMR) Magnet System

by Jennifer Reilly, Senior Safety Consultant, Safety Partners, Inc.
Denise Aronson, President, Safety Partners, Inc.
Robert Vassallo, Consulting Safety Officer, Safety Partners, Inc.
Kim Caserta, Consulting Safety Officer, Safety Partners, Inc.

While nuclear magnetic resonance (NMR) spectroscopy is an important tool for determining the structure of chemical compounds, its application is not without significant risk of injury or worse. Anyone using or in the vicinity of this important tool needs to be aware of the significant hazards associated with its use.

Nuclear magnetic resonance spectroscopy is a technique that chemists utilize in research laboratories to study the structure of chemical compounds, how temperature affects the reaction of mixtures, and to accurately detect the molecular structure and function of proteins and carbohydrates. The main risks of working with NMR magnet systems come from its high magnetic field, the handling of cryogens, and high voltage/RF sources.

NMR Risks and Hazards

Nuclear magnetic resonance spectroscopy employs the use of a nuclear magnetic resonance magnet system. While NMR systems have many inherent safety features, significant hazards still exist. If these hazards are not managed safety, risks can include:

• skin burns from splashes or spills,
• asphyxiation due to leaks or spills,
• interference with medical devices, including pacemakers or metal implants, and
• the magnetic field swiftly drawing an object to the magnet, resulting in injury.

How NMRs Operate

The NMR magnet is a large vessel supported on a cushion of air by "magnet legs" to minimize mechanical vibrations. It contains a very powerful, superconducting solenoid in its electrical core. When certain metals are cooled to near absolute zero, -273C, they have no electrical resistance, making it possible for electrons to freely travel through them. As a result, the cooled metals can carry large amounts of electrical current for long periods of time without losing energy as heat.

The magnet is not plugged into an electrical outlet. The solenoid is energized when the magnet is initially installed and continues to maintain the same electrical current level indefinitely. To maintain the state of superconductivity, the solenoid must be kept at a temperature near absolute zero, -273C. To reach and maintain a temperature, the solenoid chamber is insulated by liquid nitrogen and liquid helium.

Magnetic Quench Risks

A quench in a NMR magnet is the most significant risk to NMR magnet use. The results can be injury or worse, costly downtime, and the expense of repairing or replacing the equipment.

A quench is the rapid boil off of the liquid nitrogen and liquid helium. This can occur when a metal object comes in contact with the magnet or when the magnet is bumped by a person or an object. This disruption of the magnetic field around a localized region of the superconducting coil can lead to localized heating of that area of the coil causing the superconducting wire in the coil to lose superconductivity. The increased resistance of the wire will heat the liquid helium, causing a chain reaction that heats all the liquid helium in the magnet almost at once and changing it from a liquid to a gas. When this happens, the gas expands approximately 700 to 1 in volume, risking asphyxiation as the gas leaves the magnet, quickly fills the room, and creates an oxygen-deficient environment.

NMR Magnet Safety Considerations

Below are some safety considerations when operating a NMR magnet in a research facility:

• Only trained individuals can access the NMR area.
• Maintain a safe operating distance from the magnet known as the 5-Gauss line. People should not approach this line without operator training.
• Metal objects must remain outside the 5-Gauss perimeter. NMRs continuously exert high magnetic fields that can pull metallic objects tools and equipment uncontrollably toward the magnet. Objects can become dangerous projectiles.
• Magnetic fields are produced three dimensionally from the magnet. The 5-Gauss line perimeter must also be given to the areas above and below the location of the magnet.
• Individuals with cardiac pacemakers, biostimulators, neurostimulators, medical implants, and metal prostheses must remain outside the 5-Gauss line area. The high magnetic fields can affect their operation or cause serious injury.
• Wear proper protective clothing, including thermal gloves and face protection, while handling cryogenic liquids. This will help prevent skin burns.
• Only authorized and trained personnel should refill the magnet with liquid nitrogen. This will help reduce the risk of asphyxiation due to quenching of the magnet. Obtain the services of a company that specializes in cryofills when filling the magnet with liquid helium.
• The site location of the magnet should be evaluated by trained individuals to determine the precautions and facility considerations needed for each specific location. Considerations should include ventilation and oxygen sensors.

These are just some of the key ways that you can minimize risk when using an NMR magnet. It is most important that employees are informed of safety recommendations and trained and updated on the best practices you put in place. Doing so will help prevent equipment damage and personal injury or even death.

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Safety Partners efficiently and cost-effectively implements hands-on environmental, health, and safety (EHS) programs at emerging life sciences companies. Safety Partners tailors its programs to each client's unique science, processes, procedures, and facilities, while reducing program implementation burdens. Its expertise is unmatched, clocking over 85,000 hours at over 120 New England life sciences firms.