Federal investigators probing what caused the deadly 2010 rig explosion and oil spill in the Gulf of Mexico said yesterday that they will release preliminary findings this year and a full report in early 2013.

The U.S. Chemical Safety and Hazard Investigation Board (CSB) will release two interim reports with findings and recommendations from its review, which began shortly after the Deepwater Horizon spill that killed 11 rig workers and is regarded as one of the worst environmental disasters in U.S. history.

Preliminary findings indicate that regulations and standards used by refineries onshore are significantly more stringent than those utilized at offshore operations, the agency said.

"Our final report on the tragic accident that occurred two years ago, will, I believe, represent an opportunity to make fundamental safety improvements to offshore oil and gas exploration to prevent future catastrophic accidents," Chairman Rafael Moure-Eraso said in a statement.

The agency plans to hold several public hearings on its report, the first of which is planned for July in Houston. It plans to release preliminary findings then.

The board conducts investigations into chemical facility incidents when death or serious injury occurs. It does not have regulatory authority but issues recommendations to other agencies on how policies should be changed.

The House Energy and Commerce Committee asked CSB to investigate the Deepwater Horizon spill in 2010.

The board told Greenwire last year that one area it is investigating is why the United States does not require a "safety case" hazard system for offshore drilling operations. A safety case, which most other countries mandate for offshore drilling, requires operators to submit a set of documents on potential hazards and the safety measures the operators have put in place to address them, including protocols in case an accident occurs (Greenwire, Sept. 29, 2011).

The board is also examining whether fatigue played a role in the accident. It said yesterday that Transocean Ltd.'s workers had been required to switch from 14-day shifts to 21-day shifts on board before the accident.

"CSB is examining whether this decision was assessed for its impact on safe operations," investigator Cheryl MacKenzie said.

The investigation has not been without controversy. CSB accused Transocean of not fully cooperating, a charge that Transocean has strongly denied. Transocean has, however, questioned CSB's jurisdiction.

The Department of Justice sued Transocean late last year for not complying with subpoenas, and the case went to court earlier this month (Greenwire, April 11).

Moure-Eraso said he remains optimistic that his investigation will have a significant impact.

"The CSB investigation of this tragedy will, we believe, offer unique findings and recommendations that, if adopted, would provide significantly safer operations during vital offshore drilling and production activities," he said.