UL 555S Smoke Dampers and Fail-Safe Operation

[DenverFPE]

Hi All, I am working on a retrofit job of a high rise condo building with an atrium where NC smoke dampers with electronic actuators are provided on exterior openings for atrium smoke exhaust system makeup air. The dampers are currently set to fail open during loss of normal power, which seems logical due to the fact that the dampers are part of the smoke control system. However, during the colder months when emergency power is being tested, these dampers are opening and allowing cold air to be pulled into building (stack effect) which in turn has frozen some pipes.

Looking through standards, I cannot find any requirement that says these dampers must be provided with a fail-safe operation, which makes sense considering they are required to have emergency power and fail-safe would require 3 simultaneous events. However, most of the dampers I am finding online with a UL 555S listing have fail-safe operation, which makes me think that this may be a requirement of UL 555S (which I do not have access to). I was wondering if anyone had any experience with a similar situation or any additional insight as to whether NFPA 90A/92 or the IBC or any other standards have any requirements for fail-safe operation of components of a smoke control system.

THANKS!

 

[urgross]

By NFPA 92 a fail safe sequence is not needed for testing, but the testing sequence cannot override a smoke event. No other seqeunce will have precedence over smoke event, but that does not preclude a test sequence. Manual override is also an option if programming was not performed.

 

[ChasBean1]

I don’t think the UL standard will tell you how to engineer your damper to accommodate specific building events.

My question is more related to your testing protocols. How often and how long do you test that might result in a pipe freeze?

 

[urgross]

I was not considering UL, I was referring to NFPA 92.

 

[foreigner]

NC dampers are opened when energized so I'm guessing the damper you're describing is actually a NO damper which is closed when energized. The spring at the NO damper will return the damper back to it's original position when de-energized, hence open. I recommend checking the fire code of the city which usually can be found at the city's website to find out if NO or NC dampers are specifically required. Next I would recommend scheduling the testing in warmer days of the year.

 

[cry22]

A heating coil would solve the problem, wouldn't it?

 

[ChasBean1]

urgross, my response was to the OP, not you, but sorry for bypassing you - agree with what you said... I do not believe UL-555, mechanical code, NFPA-90A or NFPA-92 say what the fail position of your damper needs to be upon removal of the damper's normal power source.

However it is good engineering practice to have the dampers go to their fail safe positions (e.g., exhaust smoke, exhaust labs with elevated bio-safety levels, or pressurize clean spaces) upon power loss.