NTSB Preliminary Findings Identify Leaking Gas Main Joint Near Zimmy’s Tavern in Union, Michigan

Updated August 20, 2026: The NTSB has released preliminary findings on the July 28 natural gas explosion that destroyed Zimmy’s Tavern in Union, Michigan and seriously injured one person.

Federal investigators found a leak at a connection point in a 2-inch natural gas main about 60 feet from the tavern. The connection, called a butt-fusion joint, is where two sections of plastic gas pipe were joined together. The gas main was installed in 1988 and was part of the local distribution system operated by SEMCO ENERGY Gas Company.

The investigation is still ongoing. Investigators are working to determine why the joint leaked, how the escaping natural gas traveled to the tavern, and whether any other factors contributed to the explosion. The leaking joint is an important new finding because it gives investigators a specific part of the gas system to examine as they work to determine what caused the explosion.

What is known about the Union, Michigan explosion

The Porter Township Fire Department was called to the tavern at about 6:30 a.m. on Tuesday, July 28. A gas leak was found at the scene, nearby residents were evacuated, and Sunset Boulevard between U.S. 12 and Wayne Street stayed closed into the evening. The 80 year old tavern was left a near total loss.

According to WNDU, a gas leak caused the explosion and fire, an attribution the station credits to the Cass County Road Commission. The same report stated that the NTSB sent a team to “investigate what it described as a natural gas fueled explosion at the location.”

ABC57 reported that a 48 year old man from White Pigeon was taken to a hospital in serious condition, and that a firefighter injured at the scene was treated and has been released. Local coverage from 95.3 MNC notes that a gas leak was discovered on scene while the exact cause remains undetermined, with the fire investigation led by state and local authorities.

The NTSB investigation will identify any gas operator, contractor, or excavator involved and determine whether the gas line was struck, damaged, or otherwise compromised.

What Did the NTSB Find After the Zimmy’s Tavern Explosion?

The NTSB found a leak at a connection in a natural gas main about 60 feet from Zimmy’s Tavern. Investigators also detected natural gas underground on nearby properties and inside a sewer near the tavern.

According to the NTSB’s preliminary findings, those gas readings were consistent with a leak in the local natural gas distribution system. AltaGas field personnel used bar-hole testing, a method that measures gas in the soil through small holes in the ground, to help locate the source.

Testing led crews to a section of underground gas main about 60 feet from the tavern. After the pipe was excavated, testing found a leak at a butt-fusion joint. A butt-fusion joint is the connection created when the ends of two plastic pipes are heated and pressed together.

The NTSB says the 2-inch gas main was made of Aldyl A polyethylene and installed in 1988. The system had a maximum allowable operating pressure of 60 pounds per square inch gauge, or psig, and was operating at about 54 psig at the time of the explosion.

Investigators recovered sections of the gas main and related components and sent them to the NTSB Materials Laboratory for additional testing. That examination may help investigators determine why the joint leaked and whether the condition of the pipe or connection contributed to the explosion.

The NTSB identifies SEMCO ENERGY Gas Company as the regulated operator of the gas distribution system. SEMCO is an indirect subsidiary of AltaGas Ltd. The Pipeline and Hazardous Materials Safety Administration (PHMSA) and the Michigan Public Service Commission are also participating in the investigation.

The preliminary findings also provide a timeline of the emergency response. Responders established a 500-foot evacuation area around the tavern at about 11:36 a.m. and later expanded it to about a quarter mile. AltaGas shut off gas to the area at about 12:07 p.m. by squeezing off a nearby gas main.

Why Pipeline Age and Material Matter in a Gas Explosion Investigation

The age and material of the gas main matter because investigators are trying to determine why the joint near Zimmy’s Tavern leaked. The main was made of Aldyl A, an older type of plastic gas pipe that has been the subject of federal safety concerns.

The NTSB says the 2-inch gas main near Zimmy’s Tavern was installed in 1988. Aldyl A polyethylene has been used in natural gas distribution systems for decades, and its characteristics can vary depending on when the pipe was manufactured.

In January 2026, PHMSA issued a safety advisory urging natural gas distribution companies to address safety risks involving older Aldyl A gas pipes after other serious incidents. That history makes the age, condition and material of the Union, Michigan gas main important areas for investigators to examine.

The NTSB recovered sections of the pipe and related components for laboratory testing. That examination may provide more information about why the joint failed and whether the condition, installation or maintenance of the gas system contributed to the Zimmy’s Tavern explosion.

What the NTSB Findings Tell Us About the Explosion

The NTSB’s preliminary findings give investigators a much clearer picture of what happened before the Zimmy’s Tavern explosion. Investigators have now identified a specific leaking joint in the natural gas distribution system and found natural gas underground near the tavern and inside a nearby sewer.

What the findings do not yet explain is why that joint leaked or exactly how the escaping gas led to the explosion. Investigators are still examining the recovered pipe and joint and may also review installation records, maintenance history, prior leak surveys, pressure data, gas-odor complaints and other evidence that could help explain what went wrong.

The NTSB investigation is focused on determining what happened and identifying safety issues. It does not decide who is legally responsible for injuries caused by an explosion. A separate legal investigation can examine the underlying evidence to determine whether the actions or failures of a gas utility, contractor, manufacturer or another company contributed to the explosion.

Federal law also limits how NTSB accident reports can be used in civil lawsuits. Under 49 U.S.C. § 1154(b), the NTSB’s Board accident report cannot be admitted into evidence or used to prove a civil claim for damages arising from the accident. That means an injured person cannot simply rely on the Board’s eventual probable cause finding to prove a lawsuit. A legal team must independently gather and analyze the evidence needed to establish what happened and who may be responsible, including physical evidence, utility and contractor records, electronic data and witness testimony.

That work can take place while the federal investigation is still underway. An injured person does not necessarily have to wait for the NTSB’s final report, which can take a year or longer. Evidence can become more difficult to obtain over time, and legal filing deadlines called statutes of limitations may continue to run while the federal investigation is underway.

Who Can Be Responsible in a Natural Gas Explosion

In a distribution gas case, responsibility rarely rests with the person who was injured or with the business that occupied the building. The parties whose conduct is examined typically include the following.

• The gas operator or utility, including how it maintained and surveyed its mains and services, how it responded to any reported odor of gas, and whether it followed its own emergency procedures.
• Any excavator or contractor working near the line, if digging damaged a pipe or a fitting.
• The company responsible for locating and marking underground lines before excavation, since a line that is never marked cannot be avoided.
• The installer or servicer of the building’s gas piping, meter set, regulator or appliances.
• A property owner or manager who knew of a gas odor or a defective appliance and did nothing about it.

The NTSB has not yet determined the probable cause of the explosion or explained why the joint leaked. Additional testing and investigation will be needed to determine what caused the leak, how the gas reached the tavern and whether any other factors contributed to the explosion.

For a dated example of how these investigations resolve, our coverage of the NTSB’s findings in the Bel Air, Maryland house explosion shows the Board tracing probable cause to a utility’s handling of a reported gas leak. In a separate April 2025 case in Lexington, Missouri, the NTSB’s preliminary report described a fatal explosion that followed a subcontractor drilling into a gas main that had not been marked. Different facts, same lesson, which is that the answer usually lies in records and physical evidence rather than in what was visible on the day.

The Evidence That Can Be Lost After a Gas Explosion

After a gas explosion, important evidence can be altered, removed or lost quickly as emergency crews secure the scene, utilities make repairs and damaged property is cleared. That is why early evidence preservation can matter in a legal investigation.

In a gas explosion case, key evidence may include the damaged section of pipe and its fittings, the meter and regulator, leak-survey and maintenance records, odorization records, excavation or 811 ticket records, pressure data, photographs and video, and logs or recordings of any earlier reports of a gas odor or suspected leak.

A legal team can take steps to preserve this evidence before repairs, cleanup or routine record-retention practices make it harder to obtain. Our gas explosion lawyers treat evidence preservation as an early priority so independent experts can evaluate what happened and why.

What Compensation May Be Available After a Gas Explosion Injury?

Compensation after a serious gas explosion injury may include medical expenses, lost income, future medical care, pain and suffering, scarring, disability and other losses caused by the explosion. What compensation is available depends on the severity and long-term impact of the injuries and who is legally responsible.

Gas explosions can cause several types of trauma at once. The force of the blast can cause broken bones, internal injuries and other physical trauma. Fire can cause severe burns, while smoke and superheated air can injure the lungs and airway. Some survivors require treatment at a specialized burn center, multiple surgeries, skin grafts and months of rehabilitation.

For people with severe burns or other permanent injuries, the effects can continue long after the initial hospitalization. Future medical care, additional surgeries, rehabilitation, chronic pain, scarring, limited mobility and the ability to return to work may all need to be considered when evaluating the full impact of an injury.

Our burn injury lawyers investigate gas explosions nationwide and work to document both the immediate and long-term consequences of serious injuries. Our explosion burn injury page explains more about the types of damages that may be available after a serious burn injury.

What an Injured Person or Family Should Do Now

1. Put medical care first. Everything else can be handled by someone acting on the family’s behalf.
2. Ask, in writing, that the pipe, fittings, meter, regulator and appliances be preserved and not discarded, cleaned or repaired before an independent examination.
3. Photograph what is safe to photograph, and write down the names of every company whose crews were on site.
4. Keep every document, including hospital records, utility bills and notices, service records, and any past complaint about a gas odor.
5. Do not give a recorded statement to an insurer or a utility representative before understanding what caused the explosion.
6. Ask a gas explosion lawyer for a free case review to learn whether an independent investigation is warranted while the evidence still exists.

Talk to a Lawyer Who Handles Gas Explosion Cases

Pritzker Hageman is a national personal injury and wrongful death firm that represents people catastrophically injured by explosions and fires, in Michigan and in every other state. We investigate the pipeline system, the operator’s records and the work of every contractor who touched it, rather than accepting the first explanation offered.

There is no cost to talk with us and no fee unless we win. Call 1-888-377-8900, text 612-261-0856, or contact us online to reach an attorney directly.