History and investigation of the chemical odors and explosion in the University Avenue sanitary sewer

Abstract

During the summer of 2022, a fire and explosion occurred in a sanitary sewer tunnel adjacent to the University of Minnesota Twin Cities campus, propelling utility maintenance covers several meters into the air and jeopardizing the safety of the public and emergency responders. The investigation into the explosion highlighted the complex variables involved in the response to sanitary sewer events. This case study outlines current approaches and proposes recommendations for agencies to be better prepared to prevent, detect, and respond to sewer-related incidents in the future. Our recommendations include the following: (1) proactive use of remote volatile organic compound (VOC) and lower explosive limit (LEL) monitoring in sanitary sewer tunnels, especially downstream of waste discharge sites; (2) incident responders should have access to instruments that measure oxygen, LEL, VOC concentration, carbon monoxide, and hydrogen sulfide; (3) better characterization of the relationship between sewer pressurization, elevation profiles, and vapor movement; (4) verification processes for oil/water separators used by industrial facilities discharging into the sanitary sewer system; (5) installation of ventilated or anchored pressure relief utility maintenance covers where allowed by code; and (6) building maintenance protocols that include regular drain flushing to keep drain traps filled. These measures are recommended to protect infrastructure and the health and safety of the public and the responders.

Keywords:

• Maintenance hole
• manhole
• LEL
• VOC
• hazardous waste
• flammable liquid

Acknowledgments

The authors would like to thank MPCA, MCES, and the City of Minneapolis for their contributions to this investigation. We also thank Peter Daszkiewicz (Construction Laborer, UMN Facilities Management) for reviewing the manuscript and Cathy Abene (Principal Civil Engineer, UMN Facilities Management) for providing technical guidance.

Data availability statement

Monitoring data were obtained by the involved agencies throughout the investigation. Data supporting the findings of this study are available from the authors [AK, NGC, CC] upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Funding for this article was provided by Health, Safety, and Risk Management at the University of Minnesota Twin Cities.