When do we require a fd-fire damper to be installed in hvac?

We need Fire Damper when Duct cross any zone or wall and reach new zone then we give fire Damper to avoid the travel or fire from one zone to another. This can also be used when duct crosses wall where there are equipments to avoid damage of equipments from fire like AHU room, Data rooms etc

Fire Dampers are installed for penetrations in walls that are Fire Rated, shafts, elec., comm. rooms and for every penetration in the slabs. You can refer to this from Architectural and Life and Safety Drawings.

Fire dampers are recommended for any ducting through wall to avoid the damage from fire spreading in the other spaces through ducts. In few cases, it also avoids the damage to the HVAC equipments.

i approved this answer of Mr. Arsalan ,, whenever there are fire zone any penetrated duct have to be equibed by fire damber ,, take care the opening itself shall also insulated by fire rated sealant

you will find dwg called fire zonning use this drawing and put your fire damber

for electrical rooms we use exhaust or fresh air fan or other A/O grille or diffuser we use motorized volume damperconnected directly with FM200 fire fighting module to close when any alarm

Mr. Muhammad Arslan Answer is correct. 

When our duct (Supply / return) pass through the wall / safety life line / entrance from01 zone to another zone, Fire damper will apply on that subjected wall. and also it will also be used to protect the equipments in case of fire.

answer of Eng.  Muhammad Arsalan Siddiqui   is enough but i need to add that 

normal duct is 1 hour fire rated or less so we should add fire damper when the duct passing through any wall 2 hour fire rated 

Fire Dampers installed in the next cases

smoke control : across the walls just before the protected staircase to prevent the smoke from entering the protected or pressurized staircase or lobby

HVAC :just before the fan coil or AHU to insure the smoke not distributed through the system if fire occurs