Manhole Explosions in New Jersey: Dangerous and Frequent

Editor’s note: This story has been updated with a quote from a PSE&G representative.

During the past two weeks, nine separate manhole explosions have rocked Montclair, stunning residents and snarling traffic in the middle of rush hour.

On March 10, seven manholes exploded on Bloomfield Avenue, creating traffic backups that stretched into neighboring towns. On March 13, another manhole launched into the air near Grove Street. Then on March 23, yet another manhole explosion stunned Montclair and caused traffic jams near Bloomfield Avenue.

As residents’ questions mount, public safety officials have generally deferred to PSE&G, the agency conducting the investigation, as to the origin of the blasts.

Following the March 10 incident, PSE&G spokeswoman Brooke Fisher stated that the utility provider concluded that their electric facilities did not malfunction. She added that that there was no evidence of natural gas near the manholes.

In an email to Patch on Thursday, Fisher stated that the investigation in Montclair is still ongoing, and the safety of their customers and employees is a top priority.

“Clearly, these incidents are dangerous and we take them very seriously,” stated Fisher.

When asked about the investigation, Fisher told Patch that in two cases, an “electric fault” was to blame, possibly caused by road salt and water. In addition, the utility discovered sewer gas in some of the manholes, which could be an additional factor.

Fisher acknowledged that for now, PSE&G is unsure of the exact cause of the recent explosions.

A DANGEROUS AND COMMON PHENOMENON

The strange reality is that exploding manholes are uncomfortably commonplace in New Jersey, as well as the rest of the nation.

In the past two months, more than a dozen manhole explosions have been reported in Montclair, Union and Newark. Other recent incidents have taken place in Red Bank, Ridgewood and Morristown.

[Where are the explosions happening in New Jersey? See Patch’s list here]

Damage from a manhole explosion can be devastating. A manhole cover can weigh between 85 and 300 pounds, and is a “significant danger to people in the vicinity” if propelled into the air after a blast, according to a Georgia Institute of Technology study. The study claimed that the energy released in the largest manhole explosions can be as powerful as 20 sticks of dynamite.

Flying manhole covers are not the only potential risk for those in the area. The fumes and smoke emanating from a manhole blast can contain PCBs or other deadly toxins, according to one report. And unvented/unignited gases such as carbon monoxide can seep their way underground into nearby buildings, creating a serious health hazard.

WHY DO MANHOLES EXPLODE?

According to HowStuffWorks.com, most manhole explosions happen when underground electric cables – some containing up to 13,000 volts of electricity - deteriorate or get damaged due to aging, corrosion or other normal wear and tear. The damaged wires heat the surrounding insulation, which can release gases – some flammable - that build up inside the enclosed manhole. Eventually, a spark from the wires can ignite the gas and cause an explosion, sending a manhole flying up to 50 feet into the air.

Manhole explosions become much more common in the winter or summer months, according to news reports. In the winter, snow removal and plowing efforts can dump tons of road salt and melted water into the streets, some of which finds its way into the manholes. And in the summer, excessive power demands can overload feeder cables, causing short circuits.

PREVENTION

According to an online publication from the Institute of Electrical and Electronics Engineers, visual inspections play little to no reduction in manhole fires or explosions.

In their report, the IEEE recommended preventative measures that included: post installation testing, duct sealing to minimize airflow, filling manholes with inert materials to minimize gas accumulation and conducting contact voltage testing to locate faults before they cause an explosion.

A Georgia Tech study recommended preventative tactics include: replacement of aging equipment, ventilation of the manhole, installing gas analyzers or arc detection equipment, and reducing the level of road salt that is applied to streets in the winter.

In addition, the Georgia Tech study suggested that mitigation efforts should include the use of tethered or grated manhole covers, as well as the replacement of outdated manhole covers to safer models.

TOWNS TAKING ACTION

The idea of replacing manhole covers with safer versions has been discussed in several cities and towns throughout the nation, but the process is not an easy undertaking.

After a recent series of manhole explosions rocked Indianapolis last week, the Indianapolis Power & Light Co. stated that they are in the process of replacing 50 to 100 manhole covers per year in the city with safer, tethered models.

The estimated time frame of the project? Six to twelve years.

Other municipalities are taking their complaints to court. After a 2010 underground blast caused $5 million damage to the Joint Free Public Library of Morristown and Morris Township and sent a nearby manhole soaring into the air, the library’s insurance carrier sued utility provider Jersey Central Power & Light, claiming that an absence of seals on the manhole contributed to the explosion.

According to court documents, plaintiffs in the lawsuit also claimed that on numerous occasions prior to the explosion, “arcing faults, when occurring in the presence of groundwater or rain water in the Morristown Underground Network, generated combustible and/or explosive gases [which] caused numerous manhole fires and explosions.”

As a result of the explosion, one year later, the state Board of Public Utilities ordered that JCP&L hire a consultant to evaluate the underground system.

Photo caption: Emergency responders and utility workers in Ridgewood secure the scene of a manhole explosion in September of 2011.

Send news tips and releases to eric.kiefer@patch.com