One hazard of living or working in New York City is exploding manhole covers. It may sound outlandish, but it happens quite frequently. One such explosion occurred last month in Brooklyn, when a pedestrian was walking his dog in the Prospect Park neighborhood on a frosty morning. The man was rendered unconscious when the heavy metal manhole cover hit him as it fell after being lifted off the manhole by the force of the explosion.
This sounds like a freak pedestrian accident, but it’s not. Consolidated Edison reported that there were 600 incidents involving manhole covers so far this year. Most of these were so-called smokers, underground fires that sometime rise to the level of outright explosions.
Not only are there more explosions than one might suspect, but they happen every winter. Why? It’s pretty simple. During the winter, streets with snow that has been treated with a de-icing agent have melted, salty water that seeps into the manholes. These underground passages hold wires, pipes, and conduits that are often old and damaged. When the melting snow falls on decaying wires, it can spark fires. That’s why manholes that have fires burning underneath are called smokers – until they explode.
Electrical cables are expected to remain good condition underground for no more than 40 years, according to a Reuters story. However, five percent of low-voltage cables in New York City were submerged before 1930. It is the oldest and largest electrical system in the country. Therefore it’s not surprising that there are 2,100 incidents each year – six per day – every year, according to Con Ed. Most of these do not cause injury, but in the winter more such incidents cause injury. In fact, ten percent of the incidents last month were considered dangerous.
In addition to the victim injured when an exploding manhole cover fell on him, a worker was endangered by an exploding manhole cover and a car caught fire when the manhole beneath began to smoke. The NYC City Council is trying to push Con Ed to spend more on modernizing its underground cable system. But with more than 98,000 miles of cable, improvements will take time.
One relatively simple fix for the problem of exploding manhole covers is installing vents that will allow trapped gasses to escape rather than build up. But again, replacing all manhole covers will take time. Con Ed is teaming up with academic partners to develop a way to identify manhole covers that are likely to explode and focus on fixing those first.