rates in linear proportion,” Harrington explains.
Therefore, Harrington strongly advises that one
air vent (manual or automatic) be installed on every
wet pipe system at a high point in order to vent the
largest expected volume of trapped air while the
system is being filled with water. In fact, NFPA 13
7.1.5 (2016) now requires one air vent in a wet-pipe
system, and Harrington even suggests considering
multiple vents as long as they are installed with the
aid of trained professionals.
If you notice that the water in your wet system
Solving Corrosion Issues
looks rusty, do not drain the system and re-flood
it again. “As the rust forms, the oxygen is being
depleted,” notes Pfaendtner. “Ideally, you’ll let that
water sit in your system and not replace it because
the potency of that water to form corrosion dimin-
ishes as the oxygen in the water is consumed.”
piping interiors every five years
may not be enough. However,
there are actions you can take to
prevent corrosion issues in your
Although they are less vulnerable to freeze damage, dry-pipe
sprinkler systems can be more
at risk of corrosion than their
wet-pipe counterparts. Despite
pressurizing pipes with air, dry-pipe and preaction systems can
never become perfectly dry. And
air in the earth’s atmosphere is
composed of 21% oxygen, which
is more than enough to kickstart
the oxidation process.
The most effective solution to generalized corrosion
in dry-pipe and preaction systems is to pump nitrogen
through pipes. Because nitrogen does not react with
metals, a nearly pure source will stop corrosion. Potter
Corrosion Solutions in St. Louis found that replacing
compressed air with 98% nitrogen gas extends the life
expectancy of a sprinkler system by 5. 3 times.
This practice requires a nitrogen generator that is
connected to the sprinkler system and keeps a stable
amount of nitrogen gas in the pipes at all times. Nitrogen
supply systems come in a variety of sizes and options
depending on the size and function of your building.
For wet systems, be aware of any locations where
the piping goes up vertically, as these are areas
where air can accumulate. “Where trapped air exists,
the percent of dissolved oxygen in the water can rise
significantly, which in turn can raise the corrosion
40 BUILDINGS 09.16
Types of Fire Sprinkler Systems
NFPA 13 (2016) is the most recent
version of fire sprinkler standards.
Included are new standards to
include air vents in wet-pipe
systems like the one pictured.
These new standards require the
installation of a single air vent
near a high point in systems using
metallic pipes. The vent allows air
to be removed from that portion
of the system to reduce corrosion
( 7.1.5 & 8. 16. 6).
The most common sprinkler
system is the wet-pipe system.
In these sprinklers, a water supply feeds pipes throughout
the system, which contain that
water until the event of a fire.
If the temperature exceeds a
specific point, the water is then
dispersed immediately from the
pipes. These systems need to be
installed in locations free of the
risk of freezing because they are
constantly filled with water.
A preaction system is connected
to a smoke or heat detector that
will allow water to enter the
piping when activated, but will
not discharge water until a set
temperature is reached. These
systems are the most common
in computer rooms and data
centers because they limit the
accidental release of water onto
valuable electronic equipment.
In locations more likely to freeze,
you should have a dry-pipe
system. After exceeding the
temperature point in a fire, the
sprinkler activates after pressurized air contained in the pipes
escapes, and then water flows
through the pipes and out of the