There are a number of challenges that face people in the fire sprinkler industry. Many of these challenges are associated with the design of fire sprinkler systems. However, there are other important challenges facing the sprinkler industry that are of interest to fire protection engineers, but could not be classified as "design" issues. This article outlines challenges in the design, standards, specifications, maintenance and education arenas and will suggest methods of dealing with these challenges.
After 130 years, one would think that the
design of fire sprinkler systems would be pretty well in hand, but
there are always new challenges surfacing. Usually, these challenges
relate to a new device being used in buildings that somehow affects the
sprinkler system, or some new commodity or hazard coming into the
marketplace. But, every once in a while, a challenge surfaces because
some long-standing practice gets questioned due to new experience, or
some long-standing problem gets a new solution based on research or a
new way of looking at the problem. A few of the more interesting and
more recent of these follow.
High Volume Low Speed (HVLS) fans have
been used in commercial occupancies for some time, yet their impact on
fire development and sprinkler system performance has been relatively
unknown until recently.
The Fire Protection Research Foundation (FPRF) conducted two series of tests.1,2
The results of these tests showed that the situation with HVLS fans was
much better than it originally appeared to be. By following some basic
installation rules for the fans, such as keeping the fans at least 36
inches (900 mm) below the sprinklers, centering the fans between four
sprinklers, and stopping the fans upon a waterflow signal from the
sprinkler system (no more than 90 seconds after discharge from the first
sprinkler), the fans do not appear to adversely affect sprinkler
Preventing Pipe From Freezing
Antifreeze systems consisting of
glycerine or propylene glycol have been used successfully in fire
sprinkler systems for more than 60 years. Their use started in small
systems protecting loading docks and attics and spread to larger systems
as the demand for sprinklers in residential occupancies and large
freezer/refrigerated storage occupancies grew. Recent experience,
confirmed by fire testing, has shown that certain concentrations of
these fluids should not be used.3
Antifreeze solutions that appear safe to
use at this time include glycerine not exceeding a concentration of 48%
by volume and propylene glycol not exceeding a concentration of 38% by
volume. Other antifreeze solutions may surface that are safe to use, but
chemicals other than glycerine and propylene glycol will need to go
through a compatibility analysis to show that they will not adversely
affect other components in the fire sprinkler system. For systems that
cannot use the known acceptable antifreeze solutions, a new challenge
will be to keep the water in these systems from freezing, or to install a
type of sprinkler system that will not have water in the piping unless a
fire occurs (dry-pipe or preaction).
Potential solutions for protecting wet
pipe from freezing include being more creative about running pipe in
interior (heated) walls and tenting insulation over piping in attic
spaces. It is also possible to run pipe in exterior walls and put
sufficient insulation between the pipe and the exterior skin of the
building. Many of these options are non-traditional and will require
coordination with other construction trades.
Sloped Ceilings in Warehouses
Almost all of the full-scale fire testing
that has been done to justify the protection criteria for storage
warehouses has been done with a horizontal ceiling. The small body of
work that has been done with sloped ceilings has indicated that the
design areas in NFPA 134 (and the predecessor storage
documents) are insufficient to control or suppress fires consisting of
the same commodities under sloped ceilings (slopes exceeding 2 in 12).
Unfortunately, it is unknown how large the design area needs to be or
how much extra flow is necessary to overcome the delay in opening
sprinklers over a fire when the ceiling is sloped.
More research is scheduled for this topic
for the near future, but not in time to be included in the 2013 edition
of NFPA 13. Until such time as data is developed, building owners of
storage warehouses with ceiling slopes greater than 2 in 12 have two
choices. The first is to install a drop ceiling that is horizontal and
place sprinklers beneath the drop ceiling. The second is to hire a fire
protection engineer to perform a dynamic analysis to determine sprinkler
criteria unique to the client's situation.
A dynamic analysis would need to take into account two consequences of the situation that the sprinklers immediately above a fire might be delayed in opening as hot gasses follow the slope of the ceiling and collect at the ridge. The first consequence is that sprinklers higher in the building and remote from the fire might open. Such sprinklers would need to be included in the design area, even if they do not contribute to fire control or suppression. A variety of sprinkler actuation models can be used to model this situation, but as with all models, must be used within their limitations.
The second consequence of the delay in opening sprinklers is
that the fire will be bigger, so a greater discharge (density, flow or
pressure) would be expected to be needed from the sprinklers over the
fire. It might be possible to estimate what might be necessary in
discharge by performing calculations on fire size (or using data from
fire tests under flat ceilings) for fires where known discharge
characteristics (k-factor and pressure) have proven to be successful.
For example, calculations or fire tests might show that a fire consisting of 20 ft (6 m) high storage of some
commodity under a sloped ceiling would have a heat release rate of 3700
BTU/s (3.9 MW) when sprinklers over the fire opened. And if calculations
or fire tests under a flat roof showed that the same commodity at 30 ft
(9 m) in height achieved a similar heat release rate of 3700 BTU/s (3.9
MW) when sprinklers over the fire opened, then that discharge criteria
(k-factor and pressure) for the 30 ft (9 m) storage under a flat ceiling
might be adequate for 20 ft (6 m) storage under a sloped ceiling. But
this flow and pressure information would still need to be applied to the
greater design area.
Rack Storage of Exposed Plastics
Another unknown regarding protection in
NFPA 13 is the protection of exposed plastics stored on racks. As far
back as the first edition of NFPA 231C,5 this issue has not
been addressed in the NFPA standards. A few years ago, some criteria
were added for protection of exposed unexpanded plastics stored over 25
ft (7.6 m) in height. For the 2013 edition of NFPA 13, the committee
will add protection criteria for storage of exposed unexpanded plastics
up to 25 ft (7.6 m) high. Presently, no information is available in the
NFPA standard for protecting exposed expanded plastics except for in the
section on "Miscellaneous Storage."
When designing for a storage facility
that has exposed expanded plastics, engineers must develop criteria on
their own. One popular way of finding criteria is to turn to sources
outside the NFPA. For many years, Factory Mutual (FM ) has published
discharge criteria to protect exposed plastics (since their clients have
this material) in their Data Sheet 8-9, "Storage of Class 1, 2, 3, 4
and Plastic Commodities".6 The FM criteria are based on
following all of the FM requirements, not just the flow and pressure at
the sprinkler. So, if one is going to use FM discharge criteria, one
should use all of the FM rules.
Flammable and Combustible Liquids
NFPA 307 has come a long way in recent times with sophisticated sprinkler discharge criteria. Before the 1990 edition, NFPA 30 only had sprinkler criteria in the annex (Appendix D). But after a number of full scale fire tests using sprinkler systems and foam/water systems, more specific criteria was moved into the body of the document.
However, NFPA 30 still does not cover all of the different combinations of commodities and containers that building owners may want to use. When a situation comes up that is not covered by any of the sprinkler protection tables in Chapter 16 of NFPA 30, the fire protection engineer needs to develop their own discharge criteria for protecting the commodity.
In addition to the design challenges discussed above, one of the most significant developments in recent years has been the publication and promulgation of standards for the design and installation of fire sprinkler systems by organizations that are not the NFPA and are not using the NFPA as a basis for their requirements. The most significant of these organizations is Factory Mutual (FM).
Prior to 2010, FM published their own standards, but they used the NFPA standards as a starting point where such standards existed. FM would publish a document showing the NFPA rules where they would delete any rules that did not apply and write in their own rules, which were almost always more stringent than the NFPA's. During this time, it was fairly easy for a sprinkler designer to comply with both FM and NFPA standards by reading the FM document and taking the more stringent of the two sets of rules.
But that all changed in 2010 when FM published their own set of standards that was independent of the NFPA standards. Since the FM documents do not follow the same format as NFPA standards, it is more difficult to lay the standards side-by-side and compare the requirements. There are some requirements in the FM standards that are no longer more stringent than the NFPA, and there are some circumstances where compliance with both documents is impossible.
One example of a situation where the FM standards are no longer as stringent as NFPA 13 is in the maximum size of a "system". NFPA 13 limits the size of a system to 52,000 sq ft (4,800 m2) per floor for light and ordinary hazard systems and 40,000 sq ft (3,700 m2) per floor for extra hazard and high-piled storage. But FM Global Data Sheet 2-0, "Installation Guidelines for Automatic Sprinklers",8 allows much more area per system. FM originally published their standards in March 2010 without any limitation to the size of a system. Then they changed their standard in January 2011 to a maximum system size of 60,000 sq ft (5,600 m2) (total, not per floor). It is possible that this requirement will change again in the future.
FM proposed the expansion of the rules in NFPA 13 to 100,000 sq ft (9,300 m2) per floor for the 2013 edition, but the committee rejected the change. Discussions regarding the rejection were based on concern for the size of the system and amount of unprotected property when a single valve was closed, the time it would take to drain such a large system and refill it when maintenance needed to be done, the amount of trapped air that would occur in such a large system, and the alarm delays that might occur in such a large volume system.
An example of a situation where it is impossible to comply with both FM standards and NFPA 13 is the installation rules for sprinklers under sloped ceilings where the slope exceeds 2 in 12. FM Data Sheet 2-0 requires the sprinklers to be installed with their deflectors horizontal (parallel with the floor) while NFPA 13 requires them to be installed parallel to the ceiling. Both organizations have interesting concerns here.
FM is concerned that the discharge from a sprinkler parallel to the ceiling slope may not protect the floor area directly under the sprinkler. This requires the sprinkler down the slope to protect more of the area under the higher slope, which further delays when water will get to the fire. FM has also expressed concerns over the downward thrust of the discharge and the ability of sprinklers to get water to penetrate the fire plume (which is vertical) if the sprinkler spray is not vertical.
On the other hand, the NFPA committee counters with the fact that sprinkler deflectors have always been installed parallel to the slope and that there has been significant positive experience with sprinklers in this position. Whatever the effects of spray patterns and downward thrust, the rule of following the slope of the ceiling is working. From a practical perspective, the installation of sprinklers parallel to the slope is easy, as the branch lines tend to follow the structural members at the roof. For sprinklers to be installed parallel to the floor when the roof is sloped may require a swing joint at every sprinkler, and the NFPA committee has not seen the data to require such an expense.
While these two respected organizations continue to work on this subject, the engineer is caught in the middle. There is no way to comply with both NFPA 13 and the FM standards on this subject at this time. Engineers should be careful to determine which set of rules they want to follow and make this clear to the sprinkler contractor through carefully written specifications.
If the engineer wants to follow the FM rules, it may take some special consideration from the Authority Having Jurisdiction. In most places in the United States, NFPA standards are adopted as law and there is no option but to follow these standards. In order to use the FM standards where they are less stringent than NFPA 13, or where they differ from NFPA 13, the AHJ will have to grant a variance or equivalency. In such cases, the engineer should not use a few of the rules from FM and then design the rest of the system to meet NFPA 13. Instead, the engineer should use all of the FM standards, in their entirety as a substitute for the NFPA rules. The FM documents are a set of rules that work well together, but only when they are used together, in their entirety, do they potentially achieve the same level of safety as the NFPA standards.
In the June/July 2011 edition of Consulting-Specifying Engineer magazine,9 there is an article on specifying sprinkler systems that matches the vision of the joint position paper10 issued by the SFPE and others on what should be included in specifications. However, feedback from the fire sprinkler industry indicates that this is more of an ideal scenario than a real one.
Fire sprinkler contractors report that the majority of specifications that they see do not include the basic criteria necessary to convey the design intent, such as the hazard classification of the occupancy, the commodity classification of any storage, or a thoughtful analysis of the adequacy of the water supply. Instead, contractors report that specifications generally show a layout of the sprinkler system that is less efficient and more costly to install than an alternate that the contractor could provide that is still in accordance with all relevant code requirements. It would appear that the engineering community has a long way to go in writing proper specifications for fire sprinkler systems.
The challenge for fire protection engineers is to make sure that they write adequate specifications, and that they reach out to fellow mechanical, civil and other engineers that are also writing sprinkler system specifications and get them to do the same. As an industry, every one in fire protection will benefit from the improved efficiencies involved in having proper specifications that do not waste the client's time and money.
Engineers may design fabulous fire sprinkler systems, but unless they are maintained properly, they may not work correctly when a fire occurs. Design engineers leave the responsibility for maintaining the system in the hands of the building owner, who often is the least knowledgeable person in the chain of quality control of fire protection systems. The challenge as engineers is to design systems with the least amount of complications and ease of maintenance.
For example, engineers can design systems to minimize the need for auxiliary drains and to make it clear where sectional control valves are installed. Likewise, engineers can write simple documents to pass over to the owner at the time of acceptance testing that explain what they have in their building, what they may need in the future, and what limitations they may have on what they can do in their own buildings. If there are antifreeze systems in the building, for example, these documents can clearly indicate the concentration of the fluid and the type of fluid they need to use for replacement. If there is storage in the building, these documents can indicate maximum heights and commodity types so that the owner knows what they can do and can pass it on to tenants or other future owners.
One interesting maintenance challenge that has come up in recent times is in the control of bedbugs. It turns out that the best way to kill bedbugs is to heat the infested room to 170°F (77°C). Unfortunately, this also has the potential to set off the sprinklers in the same room. The National Fire Sprinkler Association (NFSA) is working with the sprinkler manufacturers and the listing labs to develop a protocol for leaving the sprinklers in place and heating the rooms. Until such time as a protocol has been developed, the only way to safely heat a room is to have a sprinkler contractor remove the sprinklers and then replace them when the treatment is done. Any other action has potential consequences that may impair the sprinkler system.
All of the issues discussed previously in this article have one thing in common. Every person in the fire protection business has to stay connected to a source of information to stay educated on what the problems are and what potential solutions exist to solve those problems. In many of the circumstances discussed here, the Fire Protection Research Foundation has played a significant role in developing a solution, or in starting research that will (hopefully soon) lead to a solution.
In other cases, the National Fire Sprinkler Association and the Society of Fire Protection Engineers are sources to look to for solutions to problems. Educational opportunities present themselves in many ways. Formal training is available in classrooms and over the Internet, and less formal opportunities arise at local Chapter and national conferences. With today's quickly shifting codes, standards and research, the practicing engineer needs to stay plugged into a network of education and information to stay on top of all of the challenges, so that the client gets the best level of fire protection available.
Kenneth Isman is with the National Fire Sprinkler Association.
- Perricone, J. & Palenske, G. "HVLS Fans and Sprinkler Operation - Phase 1 Research Program." Fire Protection Research Foundation, Quincy, MA 2009.
- Palenske, G. & Verrochi, M. "High Volume/Low Speed Fan and Sprinkler Operation - Phase II Research Program." Fire Protection Research Foundation, Quincy, MA 2011.
- "Antifreeze Solutions in Home Fire Sprinkler Systems," Fire Protection Research Foundation, Quincy, MA 2010.
- NFPA 13, Standard for the Installation of Sprinkler Systems, National Fire Protection Association, Quincy, MA, 2010.
- NFPA 231C, Standard for Rack Storage of Materials, National Fire Protection Association, Quincy, MA, 1971.
FM Global Data Sheet 8-9, Storage of Class 1, 2, 3, 4 and Plastic Commodities, FM Global, Norwood, MA, 2009.
- NFPA 30, Flammable and Combustible Liquids Code, National Fire Protection Association, Quincy, MA, 2012.
- FM Global Data Sheet 2-0, "Installation Guidelines for Automatic Sprinklers," FM Global, Norwood, MA, 2011.
- Isman, K. "Specifying Fire Sprinkler Systems," Consulting-Specifying Engineer, June/July 2011.
- "The Sprinkler and the Technician - Designing Fire Protection Systems," Society of Fire Protection Engineers, Bethesda, MD, 2005.