On/off sprinkler heads

Gail Greve <gggrev [at] mail__wm__edu> wrote

>We are planning a new research library and have selected on/off
>sprinkler heads for our fire protection system.  The sprinkler heads
>will be used with a wet system.  We chose a wet system based on
>reported maintenance problems with dry systems.
>...
>Does anyone know of a library that has used on/off sprinkler heads
>for the last 5-10 years, either with or without problems?

Wet pipe sprinkler systems:

They are very effective and highly recommended to protect
irreplaceable collections. They are faster and more reliable than
any other type of automatic sprinkler system existing today.

On/Off Sprinklers

My comments refer mainly to FlowControl Sprinklers manufactured by
Central Sprinkler Corporation.

In my opinion they are an expensive luxury, require special care,
and may not be free of potential problems. Steve Bush, Director of
Security, Library of Congress, discovered an efflorescence on the
outside of some FlowControl sprinklers at the Library of Congress in
February 1992. Approximately 25% of the 18,000 sprinklers (4,500)
were exhibiting this phenomenon. Some of the sprinklers were noted
to be weeping through the sides of the sprinklers body. These heads
were manufactured and installed in 1983, and it was reported by the
manufacturer that the castings used alloy containing 34% zinc,
compared to a 5% zinc content that is typical of sprinklers. The
higher zinc content apparently made the machining of the casting
much easier. A de-zincification process seems to be taking place,
making the sprinkler bodies porous and vulnerable to weeping and
perhaps other problems such as plugging, and sudden rupture under
high pressure.

The Library of Congress sprinklers are not chrome-plated. No
problems have been observed so far with chrome-plated sprinklers.
The plating may simply be hiding the problem. It is not known
whether the alloy specifications have changed for the FlowControl
sprinklers manufactured since 1983. I believe most of the Library's
FlowControl sprinklers have been replaced with quick-response or
fast-response standard sprinklers by now.

In addition to the serious reliability issue introduced by
de-zincification, on-off sprinklers do not offer suppression
advantages to justify their substantially higher cost. Expectations
of reduced water damage are exaggerated, since on-off sprinklers
opened by fire must operate for a minimum length of time before
shutting themselves off. Whether they flow for 15 or 25 minutes will
not substantially alter the degree of water damage to collections.
This opinion is based on the National Research Council of Canada's
(NRC) experience in testing on-off sprinklers for the National
Library of Canada.

Paul Baril
Fire Protection Advisor
Canadian Conservation Institute
Heritage Services Division

                                  ***
                  Conservation DistList Instance 9:16
                  Distributed: Monday, August 14, 1995
                        Message Id: cdl-9-16-002
                                  ***