dry heads on a dry system

[GSContracting]

I have a question form a customer, a nursing home, on system design. In my experience, all heads which are on drops in a dry system need to be dry heads to prevent water from freezing in the drop because the drops will not drain through the main. The customer recently had a dry syst. installed (in Ohio) and said that the pendants covering exterior areas are not dry heads. It is a cpvc system with an oilless compressor. Can you cite a code for me to check out that covers this issue? Am a member, and have checked NFPA website, but can find nothing specific. Thanks for any help.

 

[skdesigner]

7.2.2 Sprinklers. The following types of sprinklers and arrangements shall be permitted for dry pipe systems:

(1) Upright Sprinklers
(2) Listed dry sprinklers
(3) Pendant sprinklers and sidewall sprinklers installed on return bends, where the sprinklers, return bend, and branch line piping are in an area maintained at or above 40F
(4) Horizontal sidewall sprinklers installed so that water is not trapped
(5) Pendant sprinklers and sidewall sprinklers, where the sprinklers and branch line piping are in an area maintained at or above 40F, the water supply is potable, and the piping for the dry pipe system is copper or CPVC specifically listed for dry pipe applications

I imagine you would run into an issue with the 40F requirement just about anywhere in Ohio.

 

[skdesigner]

Pardon my omission, the above quote was from the 2010 edition of NFPA 13.

 

[SprinklerDesigner2]

Having had an ohio license I have to believe what you have is a combined wet and dry system with the wet system being cpvc and dry being steel. I would have to see the "dry heads" myself but if they are outside I can not believe they are wet. Ohio has some stringent rules that they do enforce; all companies must have a license, all designers must be nicet 3 and, this is rather unique, all fitters must be individually licensed by the state fire marshal for which they must pass a written test.

Maybe it not impossible but I have problem seeing how a mess you describe could get by everyone.

 

[SprinklerDesigner2]

Also, and you can trust me on this, if If the system has been in service and wet as you described it would have frozen already.

 

[GSContracting]

I texted the guy from the nursing home that originally inquired, and he said the dry system was black pipe. He was concerned that, after the acceptance hydrotest, any of the drops and pendant heads would have water in them unless the heads were removed and piping drained. The question came up because i am replacing a 4' dry head at another facility and he wanted to know why dry heads were needed. I explained about water in drops, and he got all excited about the other system they had contracted out on.

I thank you for your replies and information, it is very much appreciated. I have the Sprinkler Systems Handbook, and have been checking 13 on the nfpa website, but things are a little vague on system design requirements for dry heads. Thanks again, Chris.

 

[PEDARRIN2]

I have designed systems in Ohio where the piping is in a heated space over an interior/exterior cold space with insulation at the ceiling level. I have used the dry sprinklers where the vertical portion of the drop is wet only if the sprinkler has actuated (like what is used to sprinkler freezer spaces. That way, the piping can be tested and drained, but the drops do not have water in them.

Could that be what your client has?

 

[LCREP]

From NFPA 25, 2011 Ed


5.3.1.1.1.6* Dry sprinklers that have been in service for 10 years shall be replaced or representative samples shall be tested and then retested at 10-year intervals.


They have a very high failure rate, so if they have not been test they should be.

 

[fireguy519345]

From the 25 handbook. Dry heads have a 50% failure rate at the end of 10 years. That is why they are tested or replaced.

You did not ask, but here is info on UL sprinkler testing

 

[GSContracting]

Thanks again for all of the information. The facility asked me to do their annuals on the systems out there, so i will get a better idea of how the system was designed. Glad i found this forum, and really appreciate your efforts. Regards, Chris