HALIFAX -- Nova Scotia environmentalists are questioning why the federal environmental protection agency has approved an offshore drilling plan that allows up to 21 days to contain a subsea blowout, when the most recent U.S. regulation requires technology to be on hand to cap the blowout within 24 hours.

A recent Canadian Environmental Assessment Agency decision on the Shell Canada Ltd. deepwater project for the Shelburne Basin exploration off southern Nova Scotia accepted a company spill containment plan that allows for capping in 12 to 21 days.

It is signed by federal Environment Minister Leona Aglukkaq.

John Davis, a critic of the project, said in an interview that Shell should have to follow a recent decision by the U.S. Bureau of Safety and Environmental Enforcement that requires it to have a vessel carrying a capping system available within a day in the Chukchi Sea offshore Alaska project.

"Our regulators are basically saying 'You don't have to have a capping device on hand. That's OK. You can store a capping device in Norway and you can take up to 21 days to cap a blowout if it occurs,"' he said.

"That is not reasonable."

Mark Butler, the policy director of the Ecology Action Centre, said in an interview that both the regions have lucrative fisheries and diverse marine life.

"Alaska has a valuable fishery and so do we. Why wouldn't we have the same requirement for Newfoundland and Nova Scotia waters?" he asked.

In the federal environmental assessment report of June 15, the agency states a blowout in the seven planned wells is unlikely and notes Shell's containment plan allows for capping and containment in 12 to 21 days.

A spokesman for Shell Canada said the company has other methods of containing a blowout asides from the large capping device that must be shipped to the site aboard a vessel.

Cameron Yost said if there is a subsea blowout in the deepwater exploration wells, then the primary barrier is the drilling fluid which helps prevent fluids entering the wellbore. There are a number of other secondary capping methods, including the use of blowout preventors, wellhead casings and applying cement.

Yost said Shell's capping stacks are located strategically throughout the world in areas where there is a high concentration of offshore oil and gas activity, such as the North Sea, the Gulf of Mexico, and Brazil.

The capping stack identified for the Shelburne project is located in Stavanger, Norway, with the back-up stack located in Brazil.

"The Norway capping stack was selected based on the shortest deployment time to the offshore project area and based on the fact that this site has the required vessels to transport the equipment and the trained staff available onsite on a 24-hour basis to provide rapid support for the deployment of the equipment," he wrote in an email.

Davis points to the major spill of the BP well in the Gulf of Mexico as an example of how unexpected events occur and the devastating consequences if the wells aren't quickly sealed off.

"The risk is too great not to have it (the capping system) available," he said. "We don't have anything for an offshore oil spill on the East Coast ... Their only plan is to spray a toxic chemical and try to disperse the oil below the surface where it's out of sight."

"These protections need to be in place."

He said there have been a number of failures with conventional blowout preventors, particularly in deepwater subsea situations.