After going through the post Do you skip a rack unit between servers? . We thought to consolidate our rack to save space and to improve cooling in lab. If we put servers without skipping a single gap between server what are the chances of electrostatic and What measures need to take to prevent electrostatic if we don't skip a rack unit between servers?
Grounded servers and grounded racks. If your servers are plugged in with proper three-prong plugs into a properly-grounded power source, then they're good. In datacenters, you will often see racks grounded to the cages around them with thick green wire.
The point is, as long as everything is grounded, you won't have a problem with static.
They make little 5$ testers at Home Depot that you can plug into a three-prong outlet and it will tell you if it is not properly grounded.
As long as your server units are earthed via their mains connection you will be fine while running. If you need to hot swap parts you should take full ESD precautions, i.e. wrist band. As you would anyway.