HILLSBOROUGH - The federal government has taken over the investigation into what sparked the massive fire at a warehouse complex in Somerset County.

The Bureau of Alcohol, Tobacco and Firearms arrived Friday in Hillsborough Township, where the inferno raged for more than 20 hours at the Somerville Business Park along U.S. 206.

The federal government owns the complex, but leases it to a company that subleases it to other businesses. 

ATF officials were back on the scene Saturday morning as firefighters searched for any remaining hotspots.

The Hillsborough fire chief says that low water pressure made fighting the fire difficult. News 12 New Jersey is told that Hillsborough Township officials alerted the federal government that the water infrastructure surrounding the complex was inadequate and potentially dangerous if a fire were to break out there.

The fire started Thursday afternoon. The smoke plume was large enough to be detected by weather radar.

Two firefighters were hurt while fighting the fire. One firefighter hurt his leg and another suffered an injury to his eye. Both firefighters are expected to be OK.

No one who was inside the complex at the time of the fire was hurt.

Hillsborough schools were closed Friday due to the amount of smoke in the area. However, officials say that the smoke cloud did not contain any extra toxins other than what is present in normal fire smoke.

The New Jersey Department of Environmental Protection and the Environmental Protection Agency continue to monitor the air quality, and say that the air remains safe.

The large complex is located near the historic Duke Farms. It once housed old military munitions. The warehouse currently stores plastic pellets. Hillsborough’s fire chief says it is these pellets that caused the fire to burn for so long.