NEW ORLEANS — Delicately manipulating a 20-foot-long shear at depths of nearly a mile, technicians successfully snipped a key riser pipe on Thursday in their effort to contain the oil spewing into the Gulf of Mexico. They prepared to cap the remaining pipe later in the day with a dome that they hoped would allow them to funnel the oil to tankers on the surface.
Adm. Thad W. Allen, who is commanding the federal response to a spill that has been called the nation’s worst environmental disaster, said at a news conference in Metairie, La., that the cut was “a significant step forward”. But he cautioned that using a shear, rather than a finer diamond-laced wire saw, as the slicing instrument resulted in a jagged cut, meaning that the containment cap will fit less snugly.
A rougher fit, he acknowledged, increases the risk that oil may escape and that the cap itself will become filled with hydrates, icelike crystals of gas and water that form at low temperatures and high pressures.
