Shell Canada has officially applied to abandon two kilometres of pipe it accidentally dropped on the ocean floor off the coast of Nova Scotia.

The pipe, known in the industry as a riser, broke free from a surface ship March 5 during a winter storm.

"Because of the unacceptable risk associated with the health and safety exposure and potential impact to human health of offshore workers, Shell does not perceive recovery of the riser ... as a viable response option," Shell Canada's exploration manager said Friday in a letter to Canada-Nova Scotia Offshore Petroleum Board.

"Considering the health and safety exposure associated with recovery, the minimal impact to other ocean users, as well as the lack of significant adverse environmental effects, leaving the riser ... in place on the seabed is Shell's safest and most appropriate response option."

Shell Canada's "lower marine riser package" is a 115-tonne piece of equipment that connects the riser to the wellhead on the sea floor. (Stantec)

The request also involves the "lower marine riser package," a 115-tonne piece of equipment intended to connect the riser to a wellhead on the sea floor. The two-storey device was also lost when it plunged to the bottom of the ocean during the incident. It is now buried beneath an estimated 40 to 50 tonnes of silt.

The statement was based on a report prepared for Shell that reviewed both the environmental impact and options involving the fallen pipe.

Stantec Consulting Ltd. said retrieving the equipment could take up to six months and would involve cutting the huge pipe about the weight of 250 school buses into pieces and hauling each piece to the surface.

The work would involve a safety risk to workers, the consultants said.

The report also stated the sea floor near the fallen riser has relatively low "overall diversity and abundance of species."

It isn't known when the offshore petroleum board will make its decision.