Three disasters caused by overuse of road salt

Testimony on Salt Safety in favor of WI Senate Bill 1019 

By David H. Thompson, Ph.D.  2/17/26 

  

We think of road salt as making us safer.  But its overuse has helped cause major disasters with many lives lost.  Because salt is often only one of several causes of a disaster, salt’s deadly role goes unnoticed.  I’m going to describe how salt helped cause three disasters. 

In 2014, when Flint, MI, switched the source of its water from Lake Huron to the Flint River, salt in the city's water soared eightfold.  Salt in the Flint River came largely from de-icing salt.

 

Poisoning in Flint, MI

Despite the increase in salt from the switch, to save money the city did not add a corrosion inhibitor to the water, as required by law. As a result, both iron and lead pipes in Flint corroded, causing leaks and millions of dollars in damage.  Most significantly, the corrosion exposed an estimated 99,000 residents in Flint to lead., including over 25,000 children. 

 

At the home of Lee-Ann Walters and her 3-year-old son, average lead levels were measured at levels sometimes exceeding the EPA criterion for "toxic waste."  

  

Lead poisoning was only the first blow from salt.  When iron pipes corrode, it causes a chemical reaction that destroys chlorine added to the water to kill bacteria. Without enough disinfectant in the water, Legionella bacteria multiplied in the pipes of McLaren Hospital, lining them with bacterial slime.  More than 90 people caught Legionnaire’s disease... Twelve of those people died.  

 

In Flint, excess salt was one link in a chain of cause and effect that led to 2 separate disasters.  Everyone has heard about the lead pipes.  Almost no one heard about salt's central role in the poisoning and the disease outbreak. It took a long time before the connection between Legionnaires disease and salt was demonstrated, so most people never realized salt played a role in the 12 deaths. 

 

Collapse in Minneapolis

In Minneapolis, salt contributed to the deaths of 12 people and injured 100 when the I35W bridge over the Mississippi River collapsed in 2007.  

The primary cause of the collapse was a design error that reduced the strength of the bridge.  Corrosion by salt then further reduced the structure’s strength. Rust added to the load by trapping debris and

moisture.  And rust covered bridge components so the design flaw wasn't noticed.  The final NTSB report noted four other contributing causes.

The lesson here is that millions of structures we depend on, from vehicles to bridges, are being weakened--and their safety margins reduced—because of road salt. 

 

Mall Collapse in Canada

Another salt disaster happened in the Canadian city of Elliot Lake in 2012.  The parking deck on the roof of a shopping mall collapsed, killing 2 and injuring 20.  The building had experienced decades of water and salt infiltration. A key steel beam supporting the parking roof had corroded to only 10% of its original thickness.  

 

An inquiry found systemic negligence, ignored engineering warnings, and long‑term deterioration. 

What seared Canadians was the muffled cries of trapped and dying victims, who could not be rescued for 39 hours. 

Rather than remembering the role of salt, most Canadians remember the negligence. 

 

The lesson from this event is how often salt damage is minimized and ignored.  

Overall, these events show that the damage resulting from salt overuse can be lethal because the damage is... 

• Complex, 
• Unpredictable,  
• Nearly invisible, and 
• Acting over a time scale of decades. 

 

These qualities make salt overuse easy to ignore. 

 

....................................... 

Sources 

 

How Michigan’s Flint River came to poison a city.  The Guardian, Jan. 18, 2016. 

 

National Transportation Safety Board (NTSB). “Collapse of I‑35W Highway Bridge, Minneapolis, Minnesota, August 1, 2007.” NTSB Highway Accident Report NTSB/HAR‑08/03. Adopted: November 14, 2008. 

 

Kimberly J. Browns. 2018. The I‑35W Bridge Collapse: A Survivor’s Account of America’s Crumbling Infrastructure. Potomac Books / University of Nebraska Press.

 

CBC News, Oct. 15, 2014. Elliot Lake fatal mall collapse comes down to 'human failure,' report says.