USE OF REDUCED PRESSURE OR VACUUM

Glassware

Hazards

Implosion and flying glass leading to cuts and lacerations. Any piece of glassware under vacuum e.g. rotary evaporators, vacuum desiccators, Schlenk lines and storage bulbs on vacuum lines has the potential to do harm following implosion.

The energy imparted to flying fragments is directly proportional to the volume of the glass vessel evacuated. It follows that the potential to do harm is also directly proportional to the volume of the glass vessel and a rotary evaporator with its associated flasks is a greater hazard than a small Schlenk tube.

It is a common misconception that so called "high vacuum" (typically 10-3 mbars or better) systems present a significantly greater hazard than everyday vacuums produced by e.g. a water pump (around 30 mbars). These may differ by four orders of magnitude but the forces to which the glassware is subjected is essentially the same i.e.

  • High Vacuum, 99.999% of atmospheric pressure.
  • Water Pump, 97% of atmospheric pressure. 

Risks and Who is likely to be injured?

In the event of glassware implosion, both the immediate user and near co-workers are likely to be injured with damage likely to be moderate (small cuts) to severe (major lacerations or eye damage).

Precautions

  • Lab coats and glasses should be worn. In certain circumstances e.g. when introducing liquid nitrogen or other cryogenic material or when warming storage tubes from low temperature, a face mask and appropriate gloves should be worn.
  • Only suitable glassware should be used: conical flasks, except the heavy walled Buchner type flasks should never be subjected to a vacuum.
  • Glassware should be free from chips, cracks or flaws that would make it unsafe to use. Particular care should be taken to spot any star cracks.
  • Volumes of 1 litre or larger must be enclosed in tape or plastic mesh to restrain fragments in case of implosion. This will normally apply to rotary evaporators, vacuum desiccators and storage bulbs on glass lines. Schlenk lines and tubes are generally of small volume and are quite robust in nature and do not require extra protection in the shape of tape or plastic mesh.
  • Glass dewars should be fully wound in tape or preferably enclosed in a metal container.
top

Metal Vacuum System

Hazards

There are fewer hazards in handling metal vacuum systems due to the very unlikely risk of implosion.

top

Pumps

Hazards

Vacuum pumps are of various kinds. The most common are oil rotary pumps and oil (or more rarely mercury) diffusion pumps of glass or metal. Turbomolecular pumps are also used but apart from being electrical equipment, these present little danger being totally enclosed.

  • Vacuum pumps are electrically powered apparatus.
  • Belt driven rotary pumps present danger of entrapment in the moving belt and pulley wheels.
  • The exhaust of rotary pumps may be contaminated chemically but will also contain an oil mist from the pump itself.
  • There is a danger of explosion if the exhausts of rotary pumps that are pumping large volumes of air or other gas are blocked or obstructed.
  • Diffusion pumps are heated to boil the pumping liquid and so present a risk of burns.
  • Glass diffusion pumps are vulnerable to breakage and if these contain mercury the danger of mercury contamination is great.

Precautions

  • The usual precautions must be taken when using electrical equipment.
  • Rotary pumps must have belt guards to prevent entrapment.
  • A trap (either a cold trap or molecular sieve) should be used between system and pump to prevent contaminants reaching the pump oil or being exhausted into the laboratory.
  • The exhausts of rotary pumps must be free from obstruction.
  • Exhaust lines must be vented to a fume hood by tubing of large enough cross section not to cause obstruction.
  • Where possible mercury diffusion pumps should be replaced by oil versions. Mercury pumps must have secondary containment.
  • The boilers of diffusion pumps must be shielded to prevent burns by contact.
  • Diffusion pump fluids may be subject to a COSHH Assessment.
top

Pump Maintenance, Changing Oil

Pump maintenance including oil changes may be carried out by users themselves or by a member of the technical staff assigned that duty.

Hazards

Pump oil possibly contaminated with solvents, mercury, corrosive or obnoxious substances.

Precautions

  • As far as possible, pump oil should be drained with the pump in a fume hood.
  • Appropriate gloves and a lab coat must be worn.
  • If there is any suspicion of contamination, the oil must be treated as hazardous waste.
  • Waste oil should normally be taken to the technician in charge of pump maintenance for proper disposal.
  • Pumps left for service by technical staff should bear a warning about possible oil contaminants.
top

Pressure Gauges

Hazards

Vacuum pressure gauges are mainly of two kinds i.e. the manometer or McLeod Gauge type which are made of glass and contain mercury or some other liquid, and electrical devices which measure pressure dependent properties such as thermal conductivity or ionisation current.

  • Danger from glass apparatus and possibly mercury.
  • Electrical equipment.

Precautions

  • Glassware gauges should be treated as indicated above under "Glassware".
  • Secondary containment must be used around systems that contain mercury.
  • Where possible, mercury should be replaced by some other less hazardous fluid.
  • Manometer fluids may be subject to a COSHH Assessment.
  • The usual precautions must be taken when using electrical equipment.

Training

The use of glassware under vacuum or reduced pressure is part of undergraduate chemistry training. For more advanced vacuum systems, users must be instructed by a person competent and experienced in their use.

Remaining Risk

This is slight if the precautions outlined above are followed. However, glass systems remain more dangerous than metal systems because of the possibility of implosion.

Emergency Procedures

In the event of injury or fire follow the procedures outlined under "What to do if" and under "Basic First Aid".


Back to Completed Risk Assessment Forms

Adapted with permission from School of Chemistry, University of Bristol 

top