Officials have revealed that reliance on blowout preventers to prevent oil leaks like the one growing in the Gulf of Mexico came under question at a Senate hearing in Washington Monday.

Before the April 20 explosion that sank the Deepwater Horizon drilling rig, operated by Transocean for BP, "there was an assumption" that a blowout preventer "would never fail and that plans were submitted based -- to the MMS (Minerals Management Service), which is a part of the Department of Interior, based on that assumption," Homeland Security Secretary Janet Napolitano told the Senate Committee on Homeland Security and Governmental Affairs.

He believes "there was a total reliance put on this blowout preventer, but in the end, like so much in life, it's a piece of equipment and they fail," Sen. Joe Lieberman, Ind-Conn., said.

He asked Coast Guard Rear Adm. Peter V. Neffenger what should be done to raise the level of preparedness for any future failure of a blowout preventer.

Neffenger said, "Well, Senator, I think that this spill raises a lot of questions like that that we're going to have to take a good hard look at. Clearly, this is beyond what we anticipated being something that could happen. We certainly never anticipated an ongoing release of this magnitude over this period of time. So I think that that is a very real question that has to be addressed.

"I think at a minimum, we are going to have to go back and look at our planning factors for future revisions of our various contingency plans," he further added. (With Inputs from Agencies)