Nitrogen Use in Attic Protection
Using Nitrogen to Combat Corrosion and Freeze-ups in Attic Spaces
Author: Scott Bodemann
Scott Bodemann is the Product Manager for South-Tek Systems, the “Leading Designer and
Manufacturer of Nitrogen Generation Technology.” Scott initiated the research and design of the
MICBlast® – Corrosion Inhibiting System for Dry and Pre-Action Fire Protection Systems (FPS)
and played a key role in the introduction of Nitrogen Generation Technology into the Fire
Protection Industry. His expertise stems from working closely with Power Plants, which have
utilized Nitrogen for years to successfully inhibit electrochemical corrosion within boiler tubes
during extended layups.
2940 Orville Wright Way
Wilmington, NC 28405
(P) 910.332.4173
(C) 484.574.6067
(F) 910.332.4178
n2blast.com
southteksystems.com/n2-blast.asp
Attics are the primary origin of the more than 400 “large loss” commercial building fires
occurring annually in the United States.1 In addition, more than 300 attic fires are reported each
year in “noncommercial” buildings, such as hotels and long-term care facilities. 2 The owners and
operators of such properties are becoming more adept to the importance of ensuring the integrity
of the dry Fire Protection Systems in their attic spaces. The improper installation of a Fire
Protection System has proven to be a catalyst for the main factors that contribute to system
malfunction or failure. In attic spaces, an incorrectly pitched FPS is highly susceptible to both
pipe corrosion and freeze-ups, which can result in system failure. Taking preventative measures,
such as utilizing supervisory Nitrogen in new and existing dry Fire Protection Systems, will
safeguard against factors that can render an attic Fire Protection System inoperable in the event
of a fire.
After hydrotesting, residual water lays dormant in the low-lying sections of an
improperly pitched FPS. Not only is water a key ingredient in the corrosion equation3, it leads to
ice blockages and freeze-ups. The presence of residual water combined with an inexhaustible
supply of oxygen in the form of compressed air creates ideal conditions for corrosion to take
place in the FPS. While this combination is harmful in Black Steel piping, it is extremely
detrimental in Galvanized. In Galvanized piping, water can deteriorate the zinc protective layer,
therefore accelerating system failure. See the following excerpt from the White Paper:
“Corrosion in Dry and Pre-action Systems: Preliminary results of long-term corrosion testing
under compressed air and nitrogen supervision”4:
1
"Large Loss Building Fires." Topical Fire Report Series Volume 12 Issue 4 June 2011: 1-12. Journal
Note: “In this topical report, large loss building fires were defined as fires that resulted in a total dollar loss of $1
million or more.”
2
"Attic Fires in Residential Buildings." Topical Fire Report Series Volume 11 Issue 6 January 2011: 1-12. Journal
3
Scott Bodemann “Corrosion Triangle.” http://www.micblast.com/why-inhibit-corrosion/corrosion-triangle/
4
Dr. Ockert J. Van Der Schijff and Scott Bodemann, “White Paper on Corrosion in Dry and Pre-action Systems:
Preliminary results of long-term corrosion testing under compressed air and nitrogen supervision,” October 2011.
p. 2.
“Unlike galvanized outdoor structures, which are wetted intermittently, the low points in
sprinkler piping (where water and condensate accumulate) are constantly wetted and the zinc
corrosion product deposits remain where they are formed. Initially, the zinc coating cathodically
protects the underlying steel, but as the zinc is oxidized, the zinc corrosion products are
deposited on the metal surface. This, in combination with a decrease in the efficiency of the
cathodic protection due to coverage of the metal surface by non-conductive oxide, eventually
results in localized penetration of the zinc coating and corrosion of the underlying steel.”
Corrosion can lead to pinhole and potentially catastrophic leaks in galvanized dry
systems. Additionally, black steel dry systems can harbor a uniform wall-thinning corrosion
mechanism commonly referred to as “scaling”. Corrosion stemming from an improper
installation may deem an FPS inoperable, endanger people and property, and result in costly
ongoing repairs.
Furthermore, compressed air supervision in the FPS creates less than ideal circumstances
due to cold temperatures (< 40◦F) in attic spaces. Dry pipe systems freeze when water is
collected in improperly pitched pipes or when condensation naturally occurs and accumulates
within the piping during warmer months. When temperatures drop, the residual water and
condensation freeze. Cold weather freeze-ups can cause ice blockages to form and sprinkler
piping to burst, severely damaging the Fire Protection System. It is also important to note that
compressed air supervision supplies air into the pipes with temperatures ranging from 180◦F to
more than 250◦F. Unlike Nitrogen, the warm compressed air cools much too quickly and
moisture develops, resulting in an ice plug and consequently, an inoperative Fire Protection
System.
The location of the attic can provide many difficulties to a sprinkler contractor during the
installation of the FPS. It is for this reason that many dry Fire Protection Systems are not
perfectly pitched during the installation. Add to the fact that most are maintained with
compressed air supervision, and one could safely argue that the majority of attics are at risk for
any of the above issues to occur.
There are two solutions to the issues noted above:
1. Completely remove all residual water and moisture from the dry or pre-action system,
thereby rendering the internal pipe surfaces completely dry. This effectively
eliminates the availability of an electrolyte, which is a prerequisite for corrosion to
occur. However, industry experience with this remedy has shown that it is virtually
impossible to achieve completely dry conditions within the sprinkler piping. These
systems are routinely flooded for initial and periodic hydrotests, resulting in
significant amounts of water remaining in the piping due to inadequate sloping or
lack of drainage points. Additionally, the internal profile of commonly used rolled
grooves for pipe fittings create a natural “trap” for moisture, even if the pipe is sloped
in accordance with the requirements of NFPA 13. Those factors, combined with the
availability of an inexhaustible source of oxygen in the compressed supervisory air to
sustain the corrosion reaction, render this method marginally effective at best.
2. Replace supervisory compressed air with an, inert, dry, supervisory gas and the
thermodynamic driving force for the cathodic oxygen reduction reaction is effectively
removed and corrosion slows down to a negligible rate. This method is based on an
understanding of basic electrochemical theory. It has proven to be very effective in
many galvanized pipe installations that have failed within three years of their original
installation.5
Nitrogen supervision can be maintained by either installing high pressure Nitrogen
cylinders or utilizing a Nitrogen generator which is a more cost effective, hands-free solution.
Over time, the cyclic venting of Nitrogen through the system will dry out all residual water in the
sprinkler piping. Computational Fluid Dynamics (CFD) modeling has proven this to be the most
effective way to displace oxygen, dry out the piping and ensure that high purity Nitrogen reaches
all branches within the FPS. Cyclically purging dry Nitrogen into the system eliminates residual
water and the presence of oxygen in a dry or pre-action Fire Protection System. The most
prevalent cathodic reaction in a typical sprinkler system is the oxygen reduction reaction. By
effectively displacing the oxygen with inert Nitrogen, the thermodynamic driving force is
removed and it slows down the corrosion reaction to a negligible rate. Nitrogen is an inert gas
with a true - 40◦F to - 70◦F dew point. Supplying supervisory Nitrogen makes certain that there
are no freeze-ups, ice blockages or plugs.
In addition, building owners realize a significantly lower total cost of ownership by
utilizing supervisory Nitrogen in their attic Fire Protection System. Studies show that as a result
of using supervisory Nitrogen instead of compressed air, the potential service life extensions of
schedule 10 galvanized and black steel pipe are 72 years (from 7 - 79 years) and 34 years (from
14 – 48), respectively.6
Every year, attic fires result in millions of dollars of property damage, hundreds of
injuries and lost lives. In order to minimize our exposure to these risks, it is important to take
preventative measures, such as accurately following NFPA 13 installation procedures, properly
maintaining the Fire Protection System, and taking action to eliminate trapped moisture and
oxygen from within the sprinkler piping. These efforts will help ensure that the Fire Protection
System works effectively in the event of an emergency, protect property and ultimately save
lives.
5
6
Ibid., p. 4-5.
Ibid., p.11