"sealed them off" is correct and usable in written English.
You can use it when you want to describe an action of completely closing something off. For example, "The border guards sealed off the tunnel to prevent anyone from entering or leaving."
They had 40 seconds left to smile – 40 seconds before an indestructible dome would slam down on their town, sealing them off from the outside world and showing them the true meaning of togetherness.
This will include the plan to stop the influx of groundwater into the reactor buildings by sealing them off behind a mile-long subterranean wall of ground frozen by liquid coolant.
The crowd was far larger than expected, and became jammed against a line of riot officers deployed to seal them off from the Kremlin, leaving a narrow opening to the rally site.
They include allowing the I.R.A. to destroy its own weapons, with verification coming from a monitoring panel, and what is called a "rust solution," of alerting the authorities to the location of munitions and sealing them off to prevent use.
Though the administration is not turning over all of its sensitive intelligence, officials say that what has been provided has enabled the inspectors to go into a number of specific facilities and seal them off before Iraqi officials could spirit away evidence that they possessed or were developing chemical, biological or nuclear weapons.
A high-tech underground ice wall will be constructed right around the reactor buildings to seal them off and stop water leaking in to the sea.
Israel conducted raids on the homes of members of this group and "prevented journalists, human rights activists, lawyers and others from access to the organization's members and center, effectively sealing them off and at the same time leaving them open to physical attacks from settlers".
But besides the Duchess's horrendous appearance, what caught the public consciousness was that it was reported that she was pumping substances like Fix-a-Flat and cement into the butts of her clients before sealing them off with Super Glue.
To do this, the cell forms a double-layered envelope around particular sections of the cell to seal them off from the rest.
