Discovery Communications is planning security upgrades to its Silver Spring headquarters after a radical environmental activist held three people hostage in the building's lobby in September. Discovery wants to install an 8-foot-tall, gated fence in its public garden and divide its lobby, with separate entrances for employees and visitors, according to company officials and documents submitted to the Montgomery County Planning Board.

The changes, Discovery says, will let it fully reopen the garden and exhibit-filled lobby to the public.

"We looked at how we can best maintain the security for Discovery and employees and keep our facility open to the public as much as possible," said Marc Parsons, director of design and implementation.

Since the Sept. 1 standoff, which ended when gunman James J. Lee was shot by police, Discovery's lobby has been closed to the public. The garden is now only open on weekend daylight hours, when employees and children at the company's day care facility aren't around.

Discovery's plans also call for more plants and trees in the garden, to lessen the visual effects of the new fence. The fence will parallel the current 6-foot-tall gated fence in the garden, but will be taller and have diamond points at the top for security, Parsons said.

The Silver Spring Citizens Advisory Committee said at a meeting this week it would support Discovery's plans.

The county planning board is scheduled to hear the proposal at a Feb. 10 meeting, department spokeswoman Valerie Burton said.