Stairwell pressurization

[sopos]

I need some help regarding NFPA. In my country it is allowed (only in some specific cases) to use the NFPA standard. The problem is that no one has any practical experience by using this standard.
One of the problems is with stairwell pressurization. For the case when all doors are closed the situation is more or less clear, but what happens when some of the doors are open? How to determine the number of open doors? Haw to calculate the air flow thru the opened door? Is this airflow defined by air velocity thru the door, by air exchange in stairwell or you assume that the pressure stays the same as in the case when the door is closed and you calculate the airflow simply by adding the door area to the area of the gaps.

[tunaguy]

Stairwell pressurization is a VERY complicated field. It's sooo difficult to get the engineer, inspector and the fire marshal to be on the same page, from start to finish. I've never been more frustrated in my life trying to satisfy the impossible. There have been some excellent posts concerning stairwell pressurization in the Controls Forum. Search Controls Forum here and see what I mean. You'll probably be more confused afterwards, so good luck.

[glennac]

Don't worry about open doors for the NFPA. It is designed for the doors closed. You have to calculate the leakage through closed doors. The door manufactures have this info for rated doors in a pressurized stairway. So relax no one can design for an open door. The required pressure when the doors are closed is designed to help prevent a much smoke entering when a door is opened for a few seconds. Worked on the design and construction of a pressurization system for several stairways in a manufacturing plant about 8 years ago. Have fun.

[sopos]

This just doesn’t make sense to me. I am momentarily working on a shopping mall with 60000m2 of tenant space on two floors and an underground garage. What are the odds that that at least one door won’t be open practically all the time? In this case a small sad fan will be helpful as there is no fan at all. But if the regulation considers only the situation when all doors are closed and doesn’t care what will happen if that is not so, I don’t have to border myself with that too.
Are you definitely sure that the fan is sized only for the leakages through the closed doors?

[glennac]

This just doesn’t make sense to me. I am momentarily working on a shopping mall with 60000m2 of tenant space on two floors and an underground garage. What are the odds that that at least one door won’t be open practically all the time? In this case a small sad fan will be helpful as there is no fan at all. But if the regulation considers only the situation when all doors are closed and doesn’t care what will happen if that is not so, I don’t have to border myself with that too.
Are you definitely sure that the fan is sized only for the leakages through the closed doors?

The doors are fire rated and have closures on them that ensure proper closing (and proper sealing also). When you open a door it will close properly otherwise it is not a fire rated door. How many doors are you going to design for that are not closed? That is what doesn't make sense.

When the job is complete you have to have test the system for proper pressurization with the doors "closed" not open or not just a little bit open. Also what provisions do you have for disabled folks to be able to open a hard closing door? Do you need this on your job? If so you would need an automatic opener (push button) on the wall to open the door to allow entrance if this is required?

The fan itself is not all that big. The ones I worked on were for four floors two of them with enclosed lobbies with double doors and a double wide stairway. The fans were sized for this and were not that huge. I'm sure one for two floors and maybe a smaller stairway without double doors would be a lot smaller.

An architect who designs stairways knows all about this and I have worked with some on sizing the fan for a pressurized stairway. Trust me on this. I'm surprised that you don't have an architect doing the stairway design who knows the fire ratings needed.

Perhaps you can get to another site for architects and ask the question. They will tell you the same though because I have worked with them on this. Thank you very much.

[sopos]

Thank you very much. This was very helpful to me.

[ga1279]

I'm not sure were you are located, but I know NFPA also has many foot notes and fpn's such as opening and closing force required to operate the door. In Houston the Fire Inspector may choose whatever scenario he feels justified in using. Then if you're going after an occupancy permit, you then get to have ADA requirements which tend to fight the NFPA on certain conditions. Single action automatic locking doors that must must default to open status during emergency situations. I had several large buildings that failed this one as they wanted the doors to latch and have to be turned to release while pushing against the panic bar and that two actions not one.-GEO

[tech45]

I got sucked into this " fiasco " on a project about a year ago. The stairway pressure fans were on VFD's with intrigal PID controllers. I was " tasked " with tuning these things , while not having any idea what I was doing. In the end I used the drives " ramp time " ( outside of the PID ) to account for opening doors. We used a belt tensioning tool ( automotive ) to test for door pull force.

I guess the main thing that helped me was speaking to the fire marshall before the test.