Centrifuges are used in many aspects of laboratory research to separate or concentrate particles in a liquid medium. Tubes/bottles of samples are placed in balanced positions in rotors (the mobile part of a centrifuge); when loaded rotors are rapidly spun by a centrifuge, constituents in the samples will sediment differently according to their physical properties, and the sample’s density and viscosity. Some centrifuges are refrigerated to reduce the frictional heat created by this process.
- Microfuge or microcentrifuge – Small benchtop centrifuge that accommodates small tubes with capacities of 250 microliters to 2.0 milliliters; spins up to 15,000 rpm.
- Benchtop – Counter-top models typically spin from 10,000 to 20,000 rpm.
- High speed centrifuge – Usually floor model; spins at 26,000 to 30,000 rpm.
- Ultracentrifuge – Usually floor model; spins up to 100,000 to 150,000 rpm.
Rotors for centrifuges typically are made of dense, heavy material to create momentum when spinning, and thus require less energy input to keep spinning. Rotors are often stored in refrigeration to keep them at or near centrifuge refrigeration temperatures.
Different makes and models of centrifuges use different rotors, and each model comes with a table or graph that relates centrifugal force to rotational speed (rpm) for each rotor or swing bucket it can use.
Things to consider:
- DO NOT EXCEED THE PARAMETERS ON THESE TABLES/GRAPHS WHEN SETTING CENTRIFUGATION CONDITIONS.
- ONLY USE THE SPECIFIC ROTORS AND BUCKETS LISTED ON THESE TABLES/GRAPHS WITH A PARTICULAR CENTRIFUGE; using a rotor that is not designed for a centrifuge is hazardous. It also could ruin both rotor and centrifuge.
- A given centrifuge typically offers several rotor or bucket types/sizes for flexibility in choosing centrifugation conditions, and accommodating various sample containers.
The centrifugal force (expressed in number of gravities, or # xg) generated is proportional to the rotation rate of the rotor (rpm) and the distance between the rotor center and the sample tube. In lab write-ups, always record the centrifugal force used (# of gravities), and the duration of time elapsed while that force was applied; this is because centrifugal force is the only transferable unit among different centrifuges.
4.20.2 Centrifuge Hazards
- Injury or death can occur if centrifuge mechanical failure leads to loss of integrity and explosive breakup during operation. Damage leading to failures can be caused by 1) metal stress or fatigue reaching a critical state, 2) rotor corrosion or structural damage (i.e., forced loading of rotor onto a centrifuge spindle such that the alignment fittings are disabled and rotor is unmoored), 3) grossly imbalanced sample load in rotor, 4) attempted use of a rotor not designed for the unit.
- Back injury can occur from leaning over to lift heavy rotors.
- Crush injuries can occur from dropping a heavy rotor on hands/feet.
- Ensure that centrifuges and rotors receive regular preventive maintenance from a qualified service provider.
- DO NOT USE A DAMAGED ROTOR; report it to a supervisor.
- When operational problems appear (vibration, etc.), take centrifuges out of service immediately until repairs can be made.
- Keep rotors clean and free of sample residues to prevent corrosion; corrosive damage can progress over time and eventually cause structural failure. Have your service provider monitor rotors for this damage on a regular basis.
- Pay attention to your posture and plan your actions when lifting, carrying or placing heavy rotors.
Exposure hazards due to aerosolization of biohazardous materials:
Centrifuges can be used with biohazardous agents only if they are equipped with solid covers and have safety interlocks that prevent opening until the centrifuge has come to a complete stop.
Per their risk assessments, some biohazardous materials require that respiratory protection is available in case of a spill when centrifuging. If you are uncertain, check the agent’s SDS or risk assessment, or consult with EHS to determine if respiratory protection is required for spill situations.
4.20.3 General Guidelines for Centrifuging Biohazardous Material
- Use a centrifuge only after you have been trained by an experienced person on how to do it safely; it is recommended that you read applicable parts of the unit’s operations manual as well.
- Make sure that your sample containers are rated for their intended use; i.e., for the speed, temperature and chemical resistance needed.
- Wearing appropriate PPE, fill sample containers no more than ¾ full in the BSC.
- Securely close sample containers (tubes, bottles, etc.) for centrifuging.
- Always check buckets and rotors for cracks, deformities, wear or other damage, and for proper gasket/O-ring condition and placement prior to use.
- Use sealable rotors or buckets with safety cups whenever possible as an added containment barrier in case a sample container leaks during centrifugation.
- Wipe or spray exterior surfaces of sample containers with disinfectant before loading into rotor in the BSC.
- Carefully balance the sample containers in the rotor. Use a weight scale to balance pairs of tubes/bottles if necessary.
- Wipe or spray-disinfect exterior surfaces of loaded rotors/buckets before removing from BSC.
- Stop a centrifuge immediately if it begins to operate in an atypical way during your run (vibration, unusual noise).
- Wait at least 5 minutes after the spin has stopped before opening the centrifuge lid.
- Don appropriate PPE and open the centrifuge; check to see if there has been a release of sample material. If all is well, put on appropriate PPE, remove rotor to BSC, remove samples, and clean any residue left in rotor by sample containers; leave rotor clean
- Decontaminate bucket/rotor surfaces and centrifuge interior surfaces after use with biohazards and return rotor/bucket to its storage area.
- After opening the centrifuge, if you see a release of liquid outside of the sealed rotor or bucket (or from primary tube/container if not using a sealed bucket or rotor), close the centrifuge immediately, inform coworkers of the spill, place a “Stay Away – Spill” sign on the unit, and wait at least 30 minutes before initiating clean up to allow aerosols to settle. Then follow instructions under section 1.9.7: Spill Occuring Inside Centrifuge.