Explosive Decomposition of an Organic Azide

Key Instruction Points

  • Review risk assessment when scaling up reactions.

  • Use engineering safeguards for containment and remote handling when using reactive materials.

Incident Description

A chemistry graduate student was isolating an organic azide (benzyltriethylammonium azide) as an intermediate in a process to synthesize a complex organic molecule to be used in a cancer treatment. (She was trying to prepare a 5-deoxy-5-azido nucleoside by azide displacement of the 5-tosyloxy derivative). Several days earlier she had isolated a small amount of this organic azide intermediate by using a rotary evaporator to drive of the reaction solvent. Approximately 0.5 grams of material were initially isolated and used to run analytical tests to demonstrate the purity of the isolated intermediate. Now that she had demonstrated that the initial steps in her synthesis process were successful she scaled up the process 20-fold in order to isolate enough organic azide to continue her synthesis.

At approximately 9:00 on a Sunday night, while working in the lab with two other graduate students, she completed the isolation of approximately seven to eight grams of organic azide in the rotary evaporator. The rotary evaporator was set upon the open bench in the middle of the laboratory.

After isolating the organic azide from a 1:1 solution of acetone and methylene chloride in the Buchi rotary evaporator, she lifted the 250 ml round bottom flask containing the organic azide from a water bath,  with the handle provided for this purpose, using her left hand, while her right reached out for the flask.

The flask exploded in her hand, shattering all of the glass associated with the rotary evaporator and glass containers close by on the lab bench. Parts of the condenser were found in a hallway approximately 15 feet away. 

Her recollection of the incident and the nature of her injuries, indicate that she did not have the opportunity to break the vacuum on the system or stop the rotation of the flask.  It is believed that the raising of the flask alone from the warm water bath initiated the decomposition of the shock sensitive organic azide, perhaps by creating a movement in a contaminated ground glass joint. However, the graduate student does not feel that solvent "bumping" occurred in this case. This could have caused the azide compound to contaminate the glass joints.

Injuries and Property Damage Caused by the Incident

The glass fragments from the exploding flask severely lacerated the graduate student's right hand and cut her cheek and forehead. The force of the explosion blew her to the floor where she lay stunned and bleeding. The safety glasses she was wearing protected her eyes from glass fragments; otherwise she may have been blinded. The two students with her immediately came to her aid and called an ambulance that transported her to the hospital five minutes away. That night a four-hour surgical operation removed the glass from her face and hand and subsequent surgery restored most, but not all, of the functionality of her hand. She lost the ability to move her thumb. She also underwent multiple plastic surgery operations to improved her appearance.

The local fire department responded, and because the incident involved an explosion, the State Fire Marshall's office was also called in. Three University EHS employees took part in the six-hour investigation with the three state inspectors and two representatives of the local fire department. The building was closed until the investigation was complete. Upon completion of the State Fire Marshall's investigation, EHS employees cleaned up the spilled materials and blood.

Cause of the Incident

The explosion was caused by the rapid decomposition of the organic azide which it is believed had worked its way into the ground glass joints between the product flask and the glass column on the rotary evaporator. However, after interviewing the graduate student it was apparent that several factors lead up to the incident including:

  • The graduate student had underestimated the risks associated with the material she was isolating. Although she was aware generally of the decomposition potential of azides she did not know just how shock sensitive the organic azide she was isolating was, even though this information was available in the literature.

  • Due to the underestimation of risk, she isolated the azide on open bench with out adequate containment such as a laboratory hood and shielding, personal protective equipment, or procedures.

  • She did not reassess the risk when scaling up her reaction. If she had, she would have realized that the material being handled had significant explosive power and due to its inherent instability required substantial shielding and remote handling.

Recommendations    

To prevent future accidents of this type the following steps were taken: 
  • The types of "high-risk" reactions that were being conducted in the Chemistry Department were identified. Based on the type of reaction and the scale (quantity of material), the appropriate safety precautions (both engineering controls and personal protective equipment) were identified and placed in a matrix. This safety precaution matrix table was distributed throughout the Chemistry Department and required to be followed.

  • A formal peer safety review process was established that required the following steps be completed before graduate students were allowed to beginning research:

    • A comprehensive literature review must be conducted (safety and chemistry)
    • A protocol safety review form summarizing the hazards and precautions to be taken is completed
    • The planned research, information uncovered in the literature review, and safety review form, is reviewed with a peer.
  • A shared-use facility was established in which high-risk reactions could be performed and special procedures for performing these reactions established.