An explosion at a construction site in Piscataway sent four workers to the hospital. Two of those people were seriously injured, according to Mayor Brian Wahler.

The explosion happened Friday afternoon on the River Road overpass just off Interstate 287. Wahler says crews were testing a new pipe that had just been installed with air to make sure it could withstand pressure.

The project has been ongoing and is expected to wrap up by this summer.

“When they install the lines, they do it in 15-foot sections and it gets soldered, and they pressure test it each time. They move along to make sure it can handle the pounds of pressure as if natural gas was running through the line. And that’s when the explosion occurred,” the mayor said.

There was no natural gas in the line and is no harm to the public at this time. OSHA is investigating.