Lessons Learned

Trimethylsilyl azide explosion and injury incident at University of Minnesota

Incident

On Tuesday, June 17, 2014, a 5th-year chemistry graduate student was working on a procedure to generate trimethylsilyl azide in a fume hood. The procedure was a modification of several previously published versions.^[1] An explosion occurred, after which the student was taken to a hospital for burns and wounds from glass shards. (Comment: The student was released from the hospital and returned to work the next week.) The blast broke all sides of the fume hood, damaged the neighboring hood and broke an exterior window. No secondary fires or other chemical spills occurred.

Investigation

Following the incident, the Department of Chemistry in conjunction with the Department of Environmental Health and Safety conducted a thorough investigation. The investigation consisted of a series of in-person interviews, meetings, and email requests. The incident has been evaluated for contributing factors and root causes and finally recommendations for corrective and preventive actions. The full details of the investigation are being tabulated and will be prepared for publication to further share our learnings. 

It is impossible to definitively know the direct cause of the release of energy. However, we believe the most likely direct cause was either the formation and detonation of hydrazoic acid or overheating of sodium azide. Hydrazoic acid could have formed if water was introduced during the chemical synthesis. More detailed chemistry information specific to the incident will be covered at the The Safety Zone by Chemical and Engineering News, and a good starting point is Explosion injures University of Minnesota graduate student.

Root Causes

The contributing factors identified during the investigation revealed several opportunities for improvement. After careful analysis of these factors, we’ve concluded that the primary root causes revolve around hazard evaluation. 

Specific issues relative to hazard evaluation include:

1.    Hazard information relative to physical hazards and appropriate experimental controls sometimes are insufficiently covered in reference documents (i.e., SDSs  and published synthesis procedures);

2.    Hazard analysis processes utilized by researchers sometimes do not properly consider the potential energy of reactions or consider the capacity of the experimental apparatus and capabilities of the engineering controls;

3.    Standard engineering controls (e.g., fume hoods, blast shields) may not be sufficient or appropriate controls for all reactions;

Departmental Actions

The Chemistry Department held a department-wide meeting last Friday, July 11, 2014, to discuss the incident and share recommendations. The department emphasized goals to improve risk assessment and hazard mitigation protocols. To accomplish these goals, research groups have been requested to perform an immediate review of all laboratory specific SOPs, improve communication about safety among PIs and group members (esp. reaction specific chemical hazards and risks associated with scale-up), and develop a group specific Safe Operating Card (SOC) policy.

Letters warning about previously unreported risks will be sent to journals where the synthesis of TMS Azide was published and Chemical & Engineering News.

Recommendations to the research community at-large:

1.    Update risk assessment procedures

a.    to identify factors affecting the probability and severity of an energetic event occurring

b.    to consider the capabilities of available safety controls.

To paraphrase the limitations of the Laboratory Hazard Risk Assessment Matrix according to the ACS guidance document ACS Identifying & Evaluating Chemical Hazards in the Research Lab, a higher degree of training is required to consistently and accurately rate the severity of consequences and probability of occurrence for a given risk and may also require a secondary assessment and or tool.

2.    Warn researchers not to assume journals include complete risk control information. Encourage researchers to check multiple sources for information about hazards and include safety sources other than the SDS and published procedures.

Examples: ToxNet‘s Hazardous Substances Data Bank and Bretherick’s

3.    Encourage researchers to perform complete risk assessments on all potentially hazardous experiments.

4.    Develop additional tools and training to help researchers assess the severity of consequences, probability of occurrence and capacity of controls.

We at the University of Minnesota are still processing the lessons learned from the incident; however, we share this as our preliminary findings and recommendations. 

^[1] (a) Birkofer, L.; Wegner, P. Organic Syntheses, 1970, 50, 107. DOI: 10.15227/orgsyn.050.0107; (b) Nishiyama, K.; Yamaguchi, T. Synthesis, 1988, 106. DOI: 10.1055/s-1988-27481; (c) Chen, C. Y.; Lee, P. H.; Lin, Y.Y.; Yu, W.T.; Hu, W.P.; Hsu, C.C.; Lin, Y.T.; Chang, Long.S.; Hsiao, C.T.; Want. J. J.; Chung, M. I. Bioorg. Med. Chem. Lett. 2013, 23, 6854. DOI: 10.1016/j.bmcl.2013.10.004.

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