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fire sprinkler systems



Herb, here are some codes and a potential option for you, from my husband, 
who's in the fire protection biz. i believe you meant to say "other than dry 
pipe: in your request, but my husband commented on those types of systems).  

FYI:  NFPA 13, Standard for the Installation of
Sprinkler Systems, will only allow pure glycerine (C.P. or U.S.P. 96.5
percent grade) or propylene glycol for sprinkler systems connected to
potable water systems.  

A mixture of 50% glycerine and 50% water protects
against freezing for temperatures down to -20.9F, while 50% water/50%
propylene glycol protects down to -26F.  Although still undesirable in the 
event of drainage to the stream, perhaps increasing the water
concentration is an option?  antifreeze systems are limited to sprinkler 
systems with a volume capacity of 40 gallons or less; so, the actual 
discharge of the non-toxic antifreeze agent would be 20 gallons or less for a 
50/50 solution.  

Even so, if toxicity is a concern, there are additional alternatives.

In general, I stear clear of utilizing antifreeze systems because the
maintenance is costly over time and you cannot always guarantee that the
mixture in the far ends of the pipes is suitable to prevent freezing.  Here
are some alternatives:

Dry Pendant Heads: Remove the existing antifreeze system and install dry
pendant heads.  If the loading dock is 7 feet wide or less, the area can be
protected with dry pendant heads extending through the heated side of the
outside wall at a 45 angle.  These heads are directly connected to wet pipe
sprinklers in the heated building.  They are designed to extend into
freezing spaces (i.e., a freezer).  The angled orientation will allow them
to throw out to the end of the canopy.  See NFPA 13, A.8.14.7

Dry Pipe Protection: Install a dry pipe valve in place of the antifreeze fill 
system.  Annual maintenance is about the same, but the environmental impacts 
are less and the guarantee against freezing is much better.  The piping may 
need to be slightly revised to ensure proper drainage (dry pipe
systems cannot have trapped piping sections - they must slope  to  inch
per 10 ft. for proper drainage).

Heat Trace & Insulate: If the antifreeze system is not too large, it can be
heat traced and insulated.  The temperature must be maintained above 40F
but less than 120F.  This is only acceptable for small unheated areas such
as a small canopy and is the least desirable of the above alternatives.

Michelle Gaither
Tech Lead, PPRC
www.pprc.org

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