Which of the following are safe work practices when working with centrifuges?

(The following has been adopted from the University of Minnesota Centrifuge Safety Fact Sheet.)

Centrifugation may present two serious hazards: mechanical failure and dispersion of aerosols.  This page describes safety and maintenance procedures to minimize centrifuge hazards.

• Train each operator on proper operating procedures, review the user manual.
• Use only rotors compatible with the centrifuge.
• Check the expiration date for ultracentrifuge rotors.  Check tubes, bottles, and rotors for cracks and deformities before each use.
• Make sure that the rotor, tubes, and spindle are dry and clean.
• Examine O-rings and replace if worn, cracked, or missing.
• Never overfill centrifuge tubes (don’t exceed ¾ full).
• Always cap tubes before centrifugation.
• Always balance buckets, tubes, and rotors properly.
• Check that the rotor is seated on the drive correctly, close the lid on the centrifuge, and secure it.
• When using swinging bucket rotors, make sure that all buckets are hooked correctly and move freely.

• Keep the lid closed at all times during operation. Never open a centrifuge until the rotor has stopped.
• Do not exceed safe rotor speed.
• The operator should not leave the centrifuge until full operating speed is attained and the machine appears to be running safely without vibration.
• Stop the centrifuge immediately if an unusual condition (noise or vibration) begins and check load balances.

• Allow the centrifuge to come to a complete stop before opening.
• Wear appropriate gloves to remove rotor and samples.
• Check inside of centrifuge for possible spills and leaks, clean centrifuge and rotor thoroughly if necessary.
• Wash hands after removing gloves.

Centrifuging Infectious Materials or Human Samples:

• Place a biohazard label on the centrifuge.
• Always wear gloves when handling tubes or rotors.
• Avoid the use of celluloid tubes with biohazards.  If celluloid tubes must be used, an appropriate chemical disinfectant must be used to decontaminate them.
• Always use sealed safety cups, safety buckets, or sealed rotors with O-ring as secondary containment if available.

• Wipe exterior of tubes or bottles with disinfectant prior to loading into rotor or bucket.  Seal rotor or bucket, remove outer gloves, and transport to the centrifuge.
• Always wait at least 10 minutes after the run to allow aerosols to settle before opening the centrifuge.  Check for possible spills or leaks.  For spills of infectious materials, see Emergency Procedures below.
• Decontaminate centrifuge interior, safety cups or buckets, and rotors if tube breakage occurs. See Emergency Procedures below.
• Include centrifugation procedure and decontamination plan in lab SOPs.

• If there is a spill in the centrifuge
• If centrifuge malfunctions
• If there is rotor failure
• If there is tube breakage

• Turn centrifuge off immediately, close the centrifuge lid.
• Notify others, evacuate the lab, close the door, post a biohazard spill sign at the lab door.
• Leave for 30 minutes to reduce the risk of aerosols.  For spill clean-up, the operator should wear proper gloves, remove debris, clean and disinfect centrifuge interior, rotors, safety cups or buckets following the manufacturer’s instructions.
• Place any contaminated protective clothing, gloves and all clean-up materials in a biohazard bag.  Wash hands and any exposed skin surfaces with soap and water.  Call 911 or seek immediate medical attention if overtly exposed to recombinant or synthetic nucleic acid molecules or Risk Group (RG) 2 infectious agents.
• • Report incidents to P.I. or Lab Supervisor and call the CHO for assistance.

Moisture, chemicals, strong cleaning agents, and other substances can promote corrosion of centrifuge parts and cause centrifuge failure.  The following are general maintenance recommendations:

• Follow manufacturer instructions for maintenance and cleaning.
• Keep the centrifuge clean and dry.
• Cleanup all non-infectious spills immediately.  For infectious spills see Emergency Procedures above.
• Decontaminate the rotor after use with biological or radioactive materials.  Use 10% bleach for 30 minutes followed by 70% ethanol and let air dry to clean rotors and cups.
• Never clean rotors and associated parts with abrasive wire brushes.
• Store the rotor upside down in a dry place, with lids or plugs removed, to prevent condensation.
• Remove adapters after use and inspect for corrosion.
• Inspect rotor regularly.  Remove rotors from use that show any sign of defect, and report it to a manufacturer’s representative for inspection.

Maintaining a Log Book:

To avoid rotor failure, keep a log book for high speed rotors recording the length of time and speed for each use.  Track and discard rotors according to the manufacturer’s recommended schedule.

By Aimee O'Driscoll, 19 December 2018

If used incorrectly, a lab centrifuge can be a dangerous piece of equipment. The biggest concerns is the potential for injury and damage if a rotor fails. The resulting flying metal fragments can cause considerable damage and pose a risk to any nearby personnel. In one case, the shock wave caused by a failed rotor blew out a laboratory’s windows. The safety shielding was unable to contain the damaged rotor and metal fragments damaged nearby equipment, walls, and the ceiling.

In addition, injury can occur if lab personnel come in contact with moving parts while the centrifuge is in use, and aerosols produced during spinning can pose potential health risks.

According to the Occupational Safety and Health Administration (OSHA), most centrifuge accidents occur as a result of user error. In order to ensure you and your colleagues remain safe, there are several precautions to take, including:

1. Use the centrifuge on a level surface
2. Check the unit before use
3. Inspect tubes before use
4. Check the maximum load tolerance and speed
5. Balance tubes correctly
6. Keep the lid closed during cycles
7. Monitor the centrifuge
8. Shut down in event of noise or vibrations
9. Wait before opening the centrifuge

In this post, we explain these factors in more detail to help you ensure the safe operation of your lab centrifuge.

1. Use the Centrifuge on a Level Surface

It’s important to use most, if not all, pieces of lab equipment on a level surface, but it’s especially important with a lab centrifuge. An uneven surface could cause the rotor to be imbalanced. Centrifuges are designed with the assumption that the axis of the rotor will be in line with the direction of gravity. If that's not the case, it would be out of balance, even before you’ve loaded the tubes.

It’s also important to have a stable surface to work on. When the rotor starts moving, it creates a rotational force in the opposite direction. The reason that the whole centrifuge doesn't start spinning in that opposite direction is that it's firmly planted on a non-moving surface. A surface which is not sturdy and stable could move in response to this force. That movement could potentially throw the centrifuge out of balance.

2. Check the Unit Before Use

Long-term exposure to moisture, salts, and aggressive chemicals can cause corrosion of the rotor and buckets. If ignored, this can even result in small holes forming, especially where there are already existing scratches and cracks.

Aside from shortening the life of your machine, corrosion can render a centrifuge unsafe to operate, and could even lead to rotor failure. Many centrifuges are manufactured such that users and other bystanders should not be injured in case of a mechanical failure. However, the centrifuge itself could end up being destroyed.

Rotors should also be inspected regularly by a trained technician. Rotors undergo metal fatigue after repeated use, but may show no visible signs of wear to the everyday user. Metal fatigue was the suspected cause in a 1999 incident at MIT, in which a rotor split down the middle part way through an application. Thankfully no one was hurt.

3. Inspect Tubes Before Use

Centrifuge tubes should be rated for temperature, speed, and chemical resistance. Before using tubes, check that they are compatible with your application and settings. Tubes should be part of a matched set that fits your centrifuge.

You should also check the condition of tubes before use. Even a tiny fracture could result in the tube breaking easily once the centrifuge is up and running. Additionally, check caps, O-rings, and adapters to ensure they’re not degraded. Any imperfection in a vessel should be considered to render it unusable in a centrifuge.

4. Check the Maximum Load Tolerance and Speed

For each unit, the manufacturer will specify the maximum load tolerance and the maximum speed. Using a larger load at the maximum speed could result in mechanical failure of the rotor, causing injury to the user.

In some cases, you can go above the maximum load tolerance but the maximum speed will need to be reduced. This should be outlined in the manual, along with instructions for calculating the adjusted maximum speed.

Note that in cases where a material can precipitate, such as with cesium chloride and other salts, the density gradient of the precipitate (not the solution) needs to be considered. A group of researchers found this out the hard way when their rotor failed due to a miscalculation.

5. Balance Tubes Correctly

Balancing tubes correctly is crucial for the safe operation of a lab centrifuge and this topic is grounds for a separate post entirely (we’ll be publishing one shortly). However, here are some basic tips:

• Load tubes symmetrically with adjacent and opposing loads balanced according to the manufacturer’s recommendations.
• When there aren’t enough tubes to balance, additional tubes filled with water or another substance can be used. The material in the “dummy” tubes should be of a similar density to the sample material.
• Balance tubes by mass, not by volume. (Although if you are using materials of similar density, as you should be, both the masses and volumes will balance.)
• Follow the manufacturer's instructions for filling tubes. For example, they will often stipulate that they not be filled more than two-thirds full.

Some units come with an imbalance sensor; when an imbalance is sensed, the unit will stop running immediately.

The Frontier FC5306 Mini Centrifuge and the Frontier FC5706 Series Multi Centrifuge both come with an imbalance sensor.

6. Keep the Lid Closed During Cycles

When the centrifuge is running smoothly, it may not make sense why closing the lid is absolutely necessary. However, the lid plays an imperative role in keeping you, other bystanders, and nearby equipment safe. Should the rotor fail, the closed unit will hopefully contain any debris and contaminants that could otherwise cause injury.

Most centrifuges come with features that ensure this safety step is followed. For example, many come with a lid lock, that can only be unlocked once the rotor has stopped completely.

The NU-C300 General Purpose 3 Liter Centrifuge and the Centrisart A-14 Micro-Centrifuges come with a lid lock.

If you really need to see what’s happening inside the centrifuge, you might opt for a unit with a clear lid for safe observation of samples.

7. Monitor the Centrifuge

For some applications, especially those that require the unit to run for a prolonged period, a lab centrifuge is considered a set-it-and-forget-it piece of equipment. However, it’s wise not to be too quick to leave the centrifuge running unattended.

It’s best to at least monitor it until the set speed has has been reached and the centrifuge appears to be running without issues. It’s likely that if anything were amiss you would spot it fairly quickly at the the start of the process.

8. Shut Down in Event of Noise or Vibrations

Tell-tale signs that there are issues with the machine are vibration or an increase in noise as compared to normal. If you observe either or both of these, you should shut the machine off immediately.

If you have already followed the advice provided above, then chances are there is something wrong with the unit and a technician needs to take a look. Remember to always wait until the machine has stopped completely before opening the lid.

9. Wait Before Opening the Centrifuge

Some samples can aerosolize during spinning, and inhalation of the aerosolized sample can cause injury or illness. For such samples, to prevent exposure to aerosols, you should wait for a period of time (OSHA advises a ten minute waiting period) before opening the centrifuge.

There may also be the danger of aerosols leaking out during processing and contaminating the lab environment. In order to combat this, you may opt to purchase a unit that has aerosol-tight gaskets.

The Z207-M Compact Microcentrifuge has the option of a hermetically sealed rotor, and the D3024 High Speed Micro-Centrifuges come with a bio-safe rotor.

Conclusion

A lab centrifuge can pose a number risks, and with most accidents being due to user error, many of these risks can be mitigated. By thoroughly reviewing your manufacturer manual and following the advice in this article, you should be able to run your centrifuge safely.