What Happened?

A new graduate student had just finished an experiment and was cleaning up. As part of this process, they decided to change the oil in the vacuum pump they just used.  The vacuum pump was a typical laboratory mechanical rotary-vane pump with a belt connecting it to a motor.  After draining the pump oil, the student noticed it was very dirty and asked another graduate student for advice. The second student suggested rinsing the oil chamber with solvent. The new graduate student then added pentane to the pump, causing a large vapor cloud to emanate from the top port.  As the student switched the pump on to agitate and clean the chamber, a large fireball erupted from the pump. Fortunately, the student was not burned. The fire self‑extinguished quickly and did not require the use of a fire extinguisher. Following the incident, the graduate student reported what had happened to their research advisor.

What went well?

• Co-workers immediately came to assist the graduate student when they saw the fire.
• A fire extinguisher was available to extinguish the fire, and the graduate students had been trained to use it.
• The incident was reported to the research advisor.
• The incident was discussed at the next lab meeting, and an SOP for vacuum pump use and maintenance was developed.

What Was The Cause?

Immediate cause: The immediate cause was introducing a highly flammable solvent (pentane) into the vacuum pump and then energizing the pump, resulting in ignition of the pentane vapor and a flash fire at the pump. Pentane is extremely flammable, with a boiling point of only 36 °C and a flash point of -49 °C. 

Underlying causes:

• Use of an inappropriate cleaning method: The vacuum pump oil chamber was rinsed with a low‑flash‑point solvent (pentane) in equipment that contains ignition sources and is not designed for internal solvent cleaning.
• Informal, peer‑based guidance: The new graduate student relied on another student’s suggestion instead of consulting the manufacturer’s instructions, a written SOP, or a supervisor.
• Lack of hazard recognition: The students did not recognize that pentane vapors could be ignited by hot surfaces, friction, or electrical components associated with the pump.
• Absence of a defined procedure for pump oil changes: There appears to have been no written, lab‑specific SOP describing safe methods for changing and, if needed, cleaning the vacuum pump oil, including explicit restrictions on the use of flammable solvents inside the pump. 

Root causes:

1. Inadequate equipment maintenance procedures: The group had not established a standardized, documented procedure for vacuum pump maintenance that incorporated manufacturer recommendations and clearly specified permitted cleaning methods and prohibited practices.
2. Insufficient training on equipment and flammable liquids: New researchers were not trained to evaluate the use of flammable solvents in the context of equipment maintenance or to treat vacuum pumps as potential ignition sources that require formal procedures.
3. Weak supervision and oversight of “routine” tasks: Routine maintenance tasks (such as changing pump oil) were delegated without clear expectations, review, or sign‑off, allowing improvisation and peer‑derived methods to substitute for approved procedures.
4. Gaps in hazard and risk assessment: Formal hazard assessments and SOP development focused on experimental processes but did not encompass support and maintenance activities, leaving these tasks uncontrolled from a safety‑management standpoint.

How Can Incidents Like This Be Prevented?

Use proper pump maintenance procedures: 

• Require that vacuum pump oil changes and cleaning follow the manufacturer’s instructions or a lab/department SOP; do not allow improvised methods.
• Specify in the SOP how to warm, drain, and refill the pump oil and how to handle used oil as hazardous waste, without introducing flammable solvents into the pump body.
• Explicitly prohibit using flammable solvents (e.g., pentane, ether, hexane) inside the pump or near hot or sparking components; state that “rinsing” the interior with solvent is not allowed.
• Emphasize that pumps should be operated away from flammable liquids and vapors and that any necessary solvent cleaning must be done externally, in a fume hood, with the pump de‑energized and using methods approved in the SOP.

Strengthen training and supervision:

• Include vacuum‑pump safety and maintenance in new‑researcher training: basic pump hazards, ignition sources, flammable solvent risks, and the requirement to consult SOPs or supervisors before changing procedures.
• Make it clear that “routine” maintenance tasks still require supervision and may not be modified based on peer advice without PI or lab‑safety approval.

Improve risk assessment and culture:

• Ensure hazard assessments and SOPs cover support tasks (like pump maintenance), not just experimental steps, and identify where flammable solvents and ignition sources might interact.
• Encourage a culture where students pause and seek formal guidance when a suggested method is new, involves flammables, or differs from written procedures.

Resources

• Vacuum Pump Maintenance