staircase pressurization fire rating

[smcsaminda]

Dear all,
I have a problem related to staircase pressurization system.
do we require fire rated components for this system. Some says, we don't require fire rated components, because this is a fresh air supply system and the ducting and other components are located in a protected space. Is that correct? please help me?

 

[MEP.Learner]

where are u practicing? Which country?

in my opinion, if the ductwork is crossing fire compartmentation, it definitely need a fire rated box up.
for example, if the ductwork running through a non protected area into the staircase, provide fire rated box up.

While the duct is already inside the staircase, i think it doesnt need to be with FR box up.
As staircase should be protected and should be one fire compartment by itself.
However i may need more detail of your architectural drawing on how u r running the ductwork.

I am sure your company should have reference on similar system from other projects.
Usually there will be a shaft with vertical duct with VCD (but no fire dampers are required) providing fresh air (or pressurization) to the stairwell.

 

[dbill74]

It depends.

Where is the fan(s) and ductwork relative to the stairwell firewalls? Stairwells are generally 2-hour fire rated or better and anything that penetrates would need to be appropriately sealed and protected.

 

[smcsaminda]

Thank you for your answers. In my design, staircase is protected for 2 hours. Air intake duct and fans are located on the roof top. That duct is connected to a masonry wall duct. The masonry duct is located inside the protected staircase. Relevant sketch is attached herewith

 

[lilliput1]

Consider adding a recirculation duct with stairwell pressure controlled automatic damper to direct part of the discharge air back to fan inlet ductwork. Damper to modulate as required to maintain design stairwell pressure. Follow ASHRAE procedure for stair pressurization system design.

 

[smcsaminda]

@lilliput1 (Mechanical)- Yes I have not shown here that part. A re-circulation duct is available as you are saying. All the components except the masonry duct and air diffusers are located on the rooftop. My problem is that, should we have fire rated components at the rooftop.
@MEP.Learner (Mechanical)- I am practicing in Sri Lanka. This requirement has not been specified in a local code.

 

[lilliput1]

Smoke damper at roof opening with smoke damper switch interlocked to stop fan. This is to prevent fan from introducing fire and smoke to the stairwell. The roof is not a fire rated assembly.