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:
- Use the centrifuge on a level surface
- Check the unit before use
- Inspect tubes before use
- Check the maximum load tolerance and speed
- Balance tubes correctly
- Keep the lid closed during cycles
- Monitor the centrifuge
- Shut down in event of noise or vibrations
- 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.
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.
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.
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.