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.