Is it okay to use the ground of the building as the ground bus of the electrostatic grounding system?
cannot.
Any auxiliary grounds present and used at the workstation (water pipes, building frames, ground stakes) must be bonded to the equipment ground. A low-resistance connector (such as a wire) should be soldered or mechanically connected to electrically connect the AC ground (equipment ground) of the building's electrical system to the auxiliary ground.
"Equipment ground is the preferred static ground connection because all electrical equipment on the workstation (soldering iron, oscilloscope, etc.) Repairing an ESDS item using a soldering iron on the bench of an inspection microscope connected to an auxiliary ground, there may be a potential difference between the tip of the soldering iron and the ESDS item. This potential difference may cause damage to the item. Any auxiliary ground present and used at the workstation ( water pipes, building frames, ground stakes) must be connected to the equipment ground. Connecting the auxiliary ground and the equipment ground together will minimize the potential difference between the two grounds.”