When the road salt seeps, sometimes the manhole covers fly

When the road salt seeps, sometimes the manhole covers fly


WASHINGTON (AP) — Call it another form of March Madness: Not flying basketballs, but flying manhole covers.

Scientific literature traces manhole explosions back nearly a century, but a series of such incidents in Indianapolis, host of the NCAA basketball championships, has authorities looking for a quick solution.

Good luck with that.

A combination of power system design, winter road salt, older electrical cable insulation and basic chemistry have triggered underground explosions in older downtowns, launching 350-pound manhole covers high in the air. One Georgia Tech engineering professor calculated the explosions could have the force of three sticks of dynamite.

“These things have been known to be launched 10 stories; they have found a manhole cover on top of a building in a certain downtown city,” said Daniel O’Neill, who advises several utilities on the problem. “They are dangerous things. There are hundreds of these things happening every year.”

The nonprofit Electric Power Research Institute’s lab in Lenox, Massachusetts, has spent the last 25 years setting off what officials there call “manhole events.” It’s not for fun. Engineers are trying to find a way to keep manhole covers from flying.

“We’re disappointed to say we’ve not yet solved the problem,” said Matt Olearczyk, manager of distribution research for EPRI. He said, his team will keep at the problem “or we’re going to die trying to fix it.”

The EPRI team has come up with partial solutions, such as latching manhole covers to the ground with a hook-and-piston system. When there’s an explosion, those covers lift a few inches to let off some pressure, but not so much as to let in oxygen to stoke the explosion.

Experts do know how and why these explosions happen amid thousands of miles of tightly bundled electrical cables.

It starts with the way electrical power is distributed in older downtowns underground. Cables are linked so that if one fails, others take over, O’Neill said.

Cable insulation can fray or kink due to age, wear and tear, high power loads during the summer and corrosive road salt. That exposes wiring, which can spark and smolder. Especially when the insulation is older and consists of an oily paper, that releases gases, including hydrogen, methane, acetylene, carbon monoxide and ethylene, O’Neill and Olearczyk said.

Then, salty or dirty water gives the electricity a path to the ground and the spark to set off explosions, O’Neill said.

That’s why O’Neill and Olearczyk say they see more blasts events during the winter and in more northerly cities. The salt is a key ingredient. Consolidated Edison once compared manhole explosions to the streets where road salt was used and found a good correlation, O’Neill said.

The expensive process of replacing the cables with plastic insulated modern cables works well, Olearczyk said.



EPRI You Tube video of manhole cover explosions: https://www.youtube.com/watch?v=oxTIoWu__-A


4 thoughts on “When the road salt seeps, sometimes the manhole covers fly”

  1. Recently on March 31st, 2017, a manhole explosion occurred in Union Square, NY which led to several underground fires. Many pedestrians thought it was a bomb. After viewing the video, it is hard to imagine how fearful these explosions sound if you’re nearby. Thankfully no one was injured in the busy area. The manhole was probably caused by a combination of road salt and old electrical wires underground, as suggested by a ConEd spokesman. This incident supports the correlation between the winter season, road salt and manhole explosions. Hopefully, the EPRI team will find an effective solution to prevent these ongoing dangerous events.


  2. I had no idea that manhole covers were actually flying, especially over and on top of buildings. It would be less shocking the manhole cover was light, but 350 pounds and on top of that it has holes on it to let air pass through it. I think it is an unheard of problem, or not well known of a problem because who would think that these manhole covers would fly; let alone come off unless done so by a person who had the equipment to do so physically. Old or overused items in everyday life can be a problem and hard to keep track of every little detail. It maybe someone’s job to look over things, however, it is still difficult and not a guaranteed thing to find all of the flaws. It is a good thing that appropriate measures are taking care of, but unfortunately, it is a problem that has not been solved.

  3. I have seen reports about incidents like this in the past, I remember seeing in the news how a man walking his dog got injured like this. The was walking his dog when a manhole exploded and landed on them. I think that Coned need to take more precaution so incidents like this don’t happen.

  4. This is really distributing — especially after watching the video from EPRI. I’m especially concerned that engineers and researchers still are not entirely sure why this happens. I think it’s a good reminder about how we sometimes build systems and products without fully understanding how they might interact in the real world. Fortunately this does not seem to be causing a massive amount of damage or fatalities, but it does raise some concerns about living in urban areas that have such vast, historic infrastructure systems.

Leave a Reply