A Bench Scale Chemical Reaction Results in an Explosion

Key Learning Points

This incident illustrates the importance of careful planning and verification of reagent and solvent mixtures when scaling chemical reactions. 

Effects of Incident

An employee suffered glass shrapnel injuries as a result of an explosion involving a reaction in a bench scale chemistry laboratory.  The explosion shattered glassware and lab fume hood sash panes.     

Description

A laboratory employee suffered multiple glass shrapnel injuries to the face, arms, chest, and eye as a result of an explosion involving a reaction with tetrahydrofuran, water, 2,6 lutidine, and mercury perchlorate hydrate inside a lab fume hood.  While the reaction mixture was stirring, the lab worker weighed out the desired amount of mercury (II) perchlorate hydrate (84 g) and then began adding the solid to the reaction flask in 5 g portions over a 10 minute period. Once the addition of the solid was complete, the individual closed the hood sashes and returned to the balance area to clean residue from the weighing operation.  As soon as he was done cleaning, he returned to the hood and noticed that the reaction mixture (which was sitting in an ice bath) was boiling and had turned black. In the next instant, a powerful explosion occurred which shattered the reaction flask, stirrer, lab jack and two hood sash panes. 
 

The lab worker was wearing safety glasses and a lab coat. A colleague assisted the individual under the safety shower for several minutes. Upon exiting the shower, the individual was led to the eye wash due to continued vision problems. Police, paramedics, firefighters, and EH&S responded to the incident. The injured worker was transported to a nearby hospital E.R. for treatment. Surgery was required to address an eye laceration. The individual was released from the hospital two days following the surgery, and made a full recovery with no vision impairment. 

Causation 

The incident investigation indicated that the reaction mixture was too concentrated. The reaction chemicals were scaled up, but the amount of solvent was not scaled up to an equivalent proportion. The amount of material used in the reaction was approximately 20 times more concentrated than the quantity specified in the literature. Electronic software was used to calculate the quantities of all reactants but not the quantity of solvent.  Additionally, the lesser amount of solvent used in this reaction made it difficult for the magnetic stirrer bar to effectively mix the relatively-insoluble perchlorate into the reaction mixture, thus leading to localized overheating and detonation.  

Corrective Actions to Prevent Reoccurrence

Laboratory staff were re-trained to recognize that solvent proportions are critical to the safe conduct of this and other experiments.  Additionally laboratory staff were advised that electronic software can be utilized to calculate the proportions of reactants, but verification of all constituents and the associated hazards with each should occur before proceeding with revision of any documented experimental components, including proportions, concentrations and temperature.