An explosion rocked Naval Weapons Station Earle in Monmouth County this morning, causing a fire and sending eight employees to the hospital with injuries, the U.S. Navy said. One worker was hospitalized with serious injuries and the seven others suffered minor injuries, the Navy said. The blast occurred inside the base's boathouse on Sandy Hook Bay in Middletown as workers were doing routine maintenance on a utility boat around 9 a.m., the Navy said. No ammunition was involved in the explosion and the damage was contained to the boathouse, the Navy said. Tria Deibert, a spokeswoman for Riverview Medical Center in Red Bank, said the hospital currently has eight patients from the base, plus a firefighter. Two of the patients are in guarded condition and the rest are in stable condition, Deibert said. The identities of the injured workers are being withheld until family members have been notified, the Navy said. The cause of the blast is under investigation.