This information is preliminary and subject to change.
Updated 19 August 2026
On July 28, 2026, shortly before 6:28 a.m. local time, Zimmy’s Tavern, a commercial building at 69608 Sunset Boulevard in Union, Michigan, was destroyed in a natural gas–fueled explosion and subsequent fire, seriously injuring one person. The Southeast Public Safety Authority Fire Authority responded to the accident, along with AltaGas Ltd. subsidiary SEMCO Energy, Inc., the natural gas operator providing service to the area.[1] In the hours after the explosion, the operator found evidence of natural gas underground on adjacent properties and inside the sewer, consistent with a leak in the gas distribution piping system. About 11:36 a.m., responders evacuated a 500-foot radius around the accident building and later expanded the evacuation to a quarter-mile radius. AltaGas shut off gas to the area by squeezing off a nearby gas main about 12:07 p.m.[2] At the time of the accident, weather conditions were clear and 71°F with no precipitation.
The natural gas distribution system in the area included 2-inch gas mains made of 1988-vintage Aldyl A polyethylene.[3] The maximum allowable operating pressure serving the area was 60 pounds per square inch, gauge (psig); the pressure at the time of the accident was about 54 psig.[4]
AltaGas field personnel conducted bar-hole testing to investigate the source of the leak.[5] They identified and excavated around the suspected leak location, a section of pipe about 60 feet from the accident building. In-situ tests identified a leaking butt fusion joint on the main.[6] Investigators recovered sections of pipeline and associated components for further testing and examination in the National Transportation Safety Board Materials Laboratory.
All aspects of the accident remain under investigation while the National Transportation Safety Board determines the probable cause with the intent to issue safety recommendations to prevent similar events.
Parties to the investigation include the Pipeline and Hazardous Materials Safety Administration, the Michigan Public Service Commission, and AltaGas.
[1] SEMCO Energy, Inc., is an indirect wholly owned subsidiary of AltaGas Ltd. AltaGas acquired SEMCO Energy in 2012, including its Michigan assets. The regulated pipeline operator involved in this accident is a division of SEMCO Energy called SEMCO ENERGY Gas Company. This report refers to parent company AltaGas throughout.
[2] (a)
Squeezing off a pipe is an emergency procedure in which responders compress a pipe with a manual or hydraulic clamp until gas can no longer flow freely. (b) A
main is a natural gas distribution pipeline that serves as a common supply for more than one service line.
[3] Aldyl A is the trade name of a polyethylene plastic piping system first manufactured in 1965 by DuPont. The exact formulation and characteristics of Aldyl A vary by vintage.
[4]
Psig, or pounds per square inch, gauge, indicates the pressure in a pipe or vessel relative to the ambient environment.
[5]
Bar-hole testing is a gas measurement technique in which a small-diameter hole is made in the ground and a gas detection probe is inserted into the hole.
[6] A
butt fusion is a permanent, heat-welded joint created by melting and pressing together two pipe ends.
