Unintended Overpressurization of Sealed Vial Results in Rupture

Key Learnings

  • Heating chemical compounds in excess of their boiling points within a sealed system may create over-pressurization hazards.

  • When planning chemical synthesis work, the presence of a sealed system should be viewed as a trigger for additional safety review.

Effects of Incident

  • Shattered glass and chemicals escaped the chemical fume hood and could have injured nearby workers.

  • Potential for chemical exposure and burns.

  • Other equipment and experiments within the hood could have been compromised.

  • Clean up efforts were required by hazmat trained personnel.


A researcher working in a chemical laboratory placed 5 ml of methyl iodide, a hazardous compound with a boiling point of 42 degrees C, in a 15 ml labeled closed glass vial along with another non-hazardous compound. The researcher set the apparatus in a lab fume hood and pulled down the sash. The researcher then heated the glass vial containing the two compounds to 150 degrees C in a Pyrex oil bath containing silicone oil, and left for the night.

In the morning, a different lab member discovered the broken oil bath and contacted safety personnel and the researcher. Industrial Hygiene and Emergency Services personnel determined there was no exposure hazard. The hood and adjoining area were then cleaned by appropriately trained personnel.


The glass vial was not rated for the pressure generated when the compound was heated and converted from a liquid to a gas. The vial was not outfitted with a pressure relief valve.

The researcher did not recognize that heating the liquid to a temperature well in excess of its boiling point could lead to pressures sufficient to break the glass vial and, therefore, did not realize that this experiment was outside the scope of the approved work plan.

The safety training for pressurized systems did not address the hazards of over-pressurization resulting from heating liquids above their boiling point in sealed systems.

The use of Pyrex containers for oil baths heated to temperatures above 100 degrees C is discouraged, as written in various safety documents.

Corrective Actions to Prevent Reoccurrence

Safety documentation and training in chemical synthesis work should include a discussion of pressurization that occurs when heating sealed systems and associated mitigation strategies.

Unattended experiments should only be allowed with a posting at the laboratory entrance describing the contents and conditions of the experiment. 

Oil baths heated in excess of 100 degrees C should be carried out in either a porcelain or metal bath container with silicone oil that is changed frequently.  Repetitive heating of silicone oil has been known to lower its flash point.