I work in a telecommunication company and need to equip the exchanges
with a fire fighting system. For the technical rooms, there is no
problem but do I need to protect offices with people with the fire
fighting system? The system will be automatic and the gas chosen is
"INERGEN". Can you also refer to existing regulations if possible.

Fire regulations are dependent on Country and state. 
Most leased building the rsponsibility falls on the Owners to supply this.

Inergen could be used throughout the building as it is safe for humans
but i think would be quite expensive.