Published: May 07, 2010 8:30 PM EDT

WASHINGTON (AP) - Federal regulators say they are going to examine whether the last-resort cutoff valves (pictured) on offshore oil wells are reliable enough in light of the explosion and massive oil spill in the Gulf of Mexico.

Deputy Director Walter Cruickshank of the Minerals Management Service said during an Associated Press interview Friday that his agency had been comfortable that the huge cutoff valves, known as blowout preventers, worked well. That was before BP PLC's Deepwater Horizon rig exploded off Louisiana on April 20 and began spewing at least 210,000 gallons of crude per day.

"Based on the record, we have felt that these were performing the job they were supposed to perform," Cruickshank said. "This incident is going to make us re-examine that assumption."

While the precise cause or causes of the explosion and ensuing spill have not been determined, investigators are focusing on the blowout preventer as one likely cause. The reliability and safety concerns surrounding the blowout preventers will be considered by a new safety board established since the Deepwater Horizon incident by the Interior Department, which oversees MMS.

Interior Secretary Ken Salazar last week ordered MMS to conduct immediate inspections of all 30 deepwater drilling rigs and 47 deepwater production platforms in the Gulf. Inspectors are checking if blowout preventers have been tested and if emergency exercises are taking place.

The machinery weigh up to 640,000 pounds and are supposed to stop uncontrolled blowouts in exploratory wells. The destroyed Deepwater Horizon rig was equipped with shearing valves to cut right through drill pipe to stop a leak. It also had a backup mechanism, known as a Deadman, meant to automatically activate the valves if workers couldn't. However, none of that equipment stopped the gusher that has dumped millions of gallons into the Gulf since the explosion. And regulators want to know why.

"Clearly this incident shows that not everything works the way it was intended, but the record prior to this point has been very strong," Cruickshank said. Despite his remark, government and industry studies, as well as the agency's own accident reports, have shown reliability problems with these valves for many years.

Cruickshank said his agency will be reviewing the capabilities and testing protocols of these valves. He said new rules may be needed, possibly requiring certification by an independent third party. Cruickshank said the agency also will reconsider its 1998 decision to roll back testing requirements for blowout preventers from weekly to biweekly.

Related:

Oil spill update for Friday, May 7, 2010