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Der Artikel präsentiert eine gründliche Untersuchung der operativen Erfahrungen mit Sprinkler- und Wassernebelanlagen in schwedischen Kirchen, wobei der Schwerpunkt auf dem Zeitraum von 2004 bis 2023 liegt. Sie unterstreicht den diskreten und doch komplexen Charakter dieser Anlagen, die häufig traditionelle und moderne Technologien kombinieren, um kulturell wertvolle Holzkirchen zu schützen. Das Dokument geht auf die technischen Herausforderungen ein, vor denen wir stehen, wie etwa die Gefahr des Einfrierens in unbeheizten Räumen, die Eignung von Frostschutzmitteln und die Komplexität von Trockenrohrsystemen. Außerdem werden die einzigartigen gestalterischen Überlegungen zum Schutz von Außenfassaden und Dächern sowie die mit diesen Systemen verbundenen Betriebs- und Wartungskosten diskutiert. Der Artikel liefert eine detaillierte Analyse unbeabsichtigter Aktivierungen, Wasserschäden und der langfristigen Leistungsfähigkeit dieser Brandschutzsysteme. Er schließt mit einer Reflexion über die gezogenen Lehren und die Bedeutung regelmäßiger Wartungen und Inspektionen durch Dritte, um die anhaltende Wirksamkeit dieser entscheidenden Sicherheitsmaßnahmen zu gewährleisten. Die angebotenen Erkenntnisse sind von unschätzbarem Wert für das Verständnis der praktischen Auswirkungen der Installation und Wartung moderner Brandschutzsysteme in historisch bedeutsamen Gebäuden.
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Diese Zusammenfassung des Fachinhalts wurde mit Hilfe von KI generiert.
Abstract
During the past 20 years, the fire protection of ancient churches in Sweden has been improved with the installation of fire detection, fire sprinkler and water mist systems. The project identified 52 churches with either traditional sprinkler or high-pressure water mist systems. The operating experiences of these systems were documented by interviews with the end users, fire protection inspectors, system installers and by study visits. Problems associated with the use of antifreeze for water mist systems were identified. Systems have experienced leakage, high system pressures during warm days and corresponding unintentional activations due to breakage of nozzles or nozzle glass bulbs. For both sprinkler and water mist systems designed as dry-pipe systems, unintentional activations have occurred during wintertime due to freezing. Testing of dry-pipe systems also revealed unacceptably long water delivery times and residual water in piping. Many of the smaller rural churches are using a high-pressure gas- (nitrogen) driven pump because the public grid is unreliable. Three suffocation incidents were documented when nitrogen was unintentionally released into the confined technical space. Two of the incidents can be described as profoundly serious. For traditional dry-pipe systems galvanized pipes are often used but cases of internal pipe corrosion and leakage from pipes were documented. The church facility managers have a key role in the daily supervision of these installations. But it requires effort, technical competence and not least a substantial deal of self-interest. For some churches, high staff turnover has contributed to a lack of competence and supervision and maintenance has been neglected. High frequency of fault alarms (operating alarms) was also perceived as a burden and is also costly. Overall, the occurrence of technical problems and excessive costs have contributed to the shutdown or even dismantling of water mist systems in ten documented cases.
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1 Introduction
In the late 1990s and early 2000s, several churches and other culturally valuable buildings in Sweden were affected by what were believed to be, and in some cases turned out to be, arson. In response to that the fire protection, especially in old wooden churches, was improved with the installation of fire detection and fire sprinkler or water mist systems.
The experiences from the installation of fire sprinkler and water mist systems in nine wooden churches conducted in the years 2004–2006 were documented in a project financed by Brandforsk, the Swedish Fire Research Board [1]. One conclusion from this project is that the installations are discreet and well executed, but that several of them are complex. For example, two churches combine water mist and traditional fire sprinkler technology, and three churches had gas-driven pump units. As all or parts of the churches are unheated, there is a risk of freezing, which requires the installation of dry-pipe systems or the use of antifreeze. Dry-pipe systems must be drainable; otherwise, there is a risk of remaining water freezing or contributing to internal pipe corrosion. In some of the churches, compressed air is therefore used to blow the pipes free of remaining water. Initial trials shows that the technology works, but practical experience over a longer period of time was lacking. The suitability and choice of antifreeze was another issue that was identified. It makes the systems more complicated, requires additional maintenance and there is a risk that antifreeze agents will damage sensitive surfaces if leaks occur.
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In the years to come, additional installations to those documented in the Brandforsk project described above were undertaken, refer to Section 4. Many of the installations were water mist fire protection systems as these systems offer certain advantages that are attractive for heritage buildings, such as their narrow pipe dimensions and low water flow rates.
2 Objective and Methodology
The objective of the project was to document operating experiences over a longer time period. The starting point was that the churches that were part of the Brandforsk project described above were included, but also other churches with sprinkler or water mist systems. Issues that were interesting to document included good technical solutions, technical problems and poor technical solutions, any water damage, operating and maintenance costs and fire incidents.
A total of 52 churches with either fire sprinkler or water mist systems were identified. The operating experiences were documented through a literature review and by interviews with end users, fire protection inspectors, fire protection consultants and system installers, as well as by site visits. Six small- and intermediate-sized rural churches were visited, five of them with high-pressure water mist fire protection systems, the sixth having a sprinkler system. Four larger city churches were visited, all four having sprinkler systems. All site visits were conducted during the autumn of 2023 and were made in connection with an audit inspection that included testing of the fire alarm system and the fire protection system. Small- and intermediate-sized rural churches are typically sized for a few hundred (or in some cases fewer) visitors and larger city churches are typically sized for approximately 1000 to 1500 visitors. The fire protection system testing included measurement of the water delivery time for dry-pipe systems and deluge systems. Additionally, automatic high-pressure water mist nozzles were dismantled from two of the churches and their glass bulbs were examined under a microscope to investigate any defects.
The Church of Sweden is divided into thirteen geographical dioceses, each with a bishop. Each diocese includes the parishes within the diocese's geographical area and is named after the episcopal seat. All residents of Sweden are registered in a parish. The Swedish word for parish (‘församling’) stands both for a geographical unit and, collectively, for the members of the Church of Sweden within that unit, i.e., congregation [2]. In January 2023, there were 1 288 parishes in Sweden and 31 parishes abroad [3]. A reference group was linked to the project. This group included members from six of the ten dioceses that have churches with sprinkler or water mist systems. Additionally, reference group members represented fire protection consultants, system installers, an insurance company offering a specific and customized solution specifically for the Church of Sweden, the National Property Board and MSB—Swedish Civil Contingencies Agency.
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The specific objects as well as company and product brands were anonymized and are described in general terms. To limit the possibilities of identifying specific churches, some of the titles of the references in this article are not given in full. All information not found through public publications was reproduced with permission from the source.
3 Installation Standards
Installation of traditional sprinkler systems in Sweden is typically done according to the European standard SS-EN 12845:2015, “Fixed firefighting systems—Automatic sprinkler systems—Design, installation and maintenance” [4] as supplemented by the recommendations in SBF 120:8, “Rules for automatic water sprinkler systems” [5] published by the Swedish Fire Protection Association in 2016. The majority of sprinkler installations described in this paper have not been constructed completely according to these norms. As an example, the protection of wooden façades and wooden roofs are not described in the norms. Instead, fire protection consultants or the specific installer have designed these parts of the installations.
Installation of water mist fire protection systems in Sweden is typically done according to the European standard SS-EN 14972–1:2020, “Fixed firefighting systems—Water mist systems—Part 1: Design, installation, inspection and maintenance” [6] as supplemented by the recommendations in SBF 503:2, “Rules for water mist systems” [7] published by the Swedish Fire Protection Association in 2023. It is noted that all the installations described in this paper were carried out before the publication of these recommendations. The European standard SS-EN 14972–1:2020 was preceded by two Technical Specifications, SIS-CEN/TS 14972:2008 [8] and SIS-CEN/TS 14972:2011 [9] and based on the latter, SBF 503:1 [10] was published in 2019. Many of the installations described in this paper were carried out before the publication of these recommendations. As such, fire protection consultants or the specific installer have designed the system installations, based on other principles or design guidance.
4 The Typical System Installations
4.1 The Number of Installations
The Church of Sweden includes in the order of 3,400 churches, and the number of churches with automatic sprinkler or water mist systems is small in that perspective. The following number of churches with fire protection systems were identified in the project:
44 small- and intermediate-sized rural churches, five with sprinkler systems and 37 (84%) with high-pressure water mist systems. For two of the churches, the interior is fitted with a high-pressure water mist system and the exterior has a deluge sprinkler system.
Eight larger city churches, seven with sprinkler systems and one with a high-pressure water mist system.
This totals 52 churches, where the majority of them (75%) are partly or fully fitted with a high-pressure water mist system. About 17 of the water mist systems are partly or completely filled with antifreeze and 15 of them have a gas-driven pump unit. The oldest of the installations was commissioned in 1996 (a sprinkler system), the newest in 2019 (also a sprinkler system). The majority of the installations were made during the ten-year period from 2004 to 2013 in small- and intermediate-sized rural churches. Most of these installations were high-pressure water mist systems.
In addition, there is an unknown number of churches having open type deluge systems with a water connection point for the fire service. The systems are used to protect attics, church towers and bell towers, in other words, spaces where fire can spread quickly and is difficult to reach with fire hoses. The systems began to be installed as early as the 1920s in some church towers in larger city churches but were replaced with modern automatic sprinkler systems around the year 2000. Many systems still exist in small- and intermediate-sized rural churches but are often in poor condition. This type of non-automatic system was out of the scope of the project.
4.2 Small- and Intermediate-Sized Rural Churches
The fire sprinkler installations in small- and intermediate-sized rural churches look quite similar. The typical installation consists of a heated and insulated plant building located near the church. In the plant building there is a water tank, one or several pumps and an electric power generator (where applicable). In some cases, the fire protection system’s section valves are installed in the plant building, in other cases these valves are possible to fit in the church. Underground pipelines run from the plant building to the church. Sometimes the pipelines are buried directly below the ground surface, but often the pipes are laid in a pipe culvert, which simplifies inspection and replacement of pipes if needed. For some churches, it is possible to find space inside the church to run the pipes hidden up to the attic. In other cases, there are no such spaces and then an external arrangement on the outside of the church may be needed. Pipework in the attic feeds internal spaces such as the church room, sacristy, and armory and, where applicable, the external façades and roofs. The pipework in the attic can thus be extensive, and since the attics are uninsulated, the pipes are exposed to both heat during summer and cold during winter.
July is usually the warmest month in the entire country and the temperature differences are small between the southern and northern parts. Heat waves with temperatures above 30 °C occur at least once every summer, even in the northern inland [11]. Winter temperatures in the central and northern parts of the country can reach − 35 °C or lower for short periods. In the southern parts of the country, winter is considerably milder, normally at a low of a few degrees below zero, although extreme temperatures lower than − 30 °C have been recorded [12].
For interior spaces and in the attic space, it is common to use either a dry-pipe system or a wet-pipe system with antifreeze and automatic sprinklers or nozzles. In churches that are fully or partially heated, there are wet-pipe systems without antifreeze. The design area typically includes 8 to 10 automatic water mist nozzles corresponding to a total water flow rate of approximately 150 l/min. The typical stand-by pressure in dry-pipe systems is about 5 bar and in wet-pipe systems it is about 25 bar. The operating pressure of the systems are between 60 and 100 bar, dependent on the make.
For façades and roofs, deluge systems with open nozzles are usual. These deluge systems are divided into sections that are activated by a separate fire detection system. A system has typically between four to eight section valves to cover all external façades and roof parts. Each deluge sections typically include approximately 5 to 10 open water mist nozzles corresponding to a total flow rate between 100 l/min and 200 l/min per section. The pump unit is typically designed for the operation of two deluge sections but is not large enough for a simultaneous fire inside the church. The most common type of fire detection system has a linear heat detection cable that short circuits (from the heat of the fire). This power failure is detected, and an electrical signal opens the correct section valve. The argument against using water mist for the exterior parts was that the smaller water droplets risked being affected by wind. For those churches (the majority) where water mist systems were actually installed externally, it is clear, however, that the nozzles’ spray pattern was optimized to make them less sensitive to wind effects. The nozzles have a spray pattern with jets that hit the façade or roof surface before the water jets are atomized into smaller water droplets. Once the water runs down the façade or roof surface, the influence of wind is small. Figure 1 shows an activation of a high-pressure water mist system deluge section with open nozzles that discharges water on a church’s clapboard roof. The day of the test was windy.
Fig. 1
The activation of one section of a high-pressure water mist system with open nozzles that discharges water on a church’s clapboard roof. The system has eight deluge sections covering all façades and ceiling roof surfaces, but the pump unit is designed for the simultaneous activation of two deluge sections
Most often, there is a lack of municipal water with the required capacity. Then a water tank with associated pumps is required. According to the recommendations in SBF 120:8, the duration of the water supply must be at least 60 min. But often this time has been reduced and adapted to the response time of the fire service. Several water mist system installations are designed for a 30-min duration and a corresponding tank capacity in the order of 2,500 L to 15,000 L, either as full capacity tanks or as reduced capacity tanks with automatic inflow from the municipal water main.
4.3 Larger City Churches
Several larger churches with (traditional) sprinkler systems were identified. As the churches are usually built of stone or brick, there are no external sprinklers, unlike for the smaller wooden churches discussed above. Another difference is that the church interior usually does not have sprinklers because the rooms are large and tall. Most commonly, sprinklers are installed in attic and tower spaces. The building construction is made of wood, and the spaces are also difficult to access for manual firefighting. Figure 2 shows an installation of a pre-action sprinkler system in the attic space of a larger city church.
Fig. 2
The attic space in a larger city church. A traditional sprinkler system (pre-action system) is installed. In this installation, the sprinkler pipes are made of stainless steel for corrosion protection reasons
Most of the protected city churches have sprinkler systems with one or two dry-pipe valves. The water supply is often fed via the municipal water mains. For tall buildings, one or more pressure boosting pumps are often required, as sufficient water capacity is available but not sufficient water pressure. The systems are typically designed to an equivalent of Ordinary Hazard Category 2 per SS-EN 12845:2015, i.e., a water density of 5 mm/min and a design area of 180 m2. This design area corresponds to at least 15 automatic sprinklers.
5 Experiences from the Installations
5.1 Fire Incidents
There are no reported fires from any of the churches.
5.2 Unintentional Activations of Interior Automatic Nozzles or Sprinklers
Several cases with activation of sprinklers or nozzles or other discharge of water without a fire have occurred, resulting in water damage in certain cases. Some of the cases and the probable reasons are described below.
Case 1: A church from the 1600s has a high-pressure water mist system installed in 2006. A dry-pipe system is installed in the church room and other interior spaces as well as in the attic. In the winter of 2021, water damage occurred when an automatic (with glass bulb) nozzle activated, and several hundred liters of water flowed into the church. Murals and furnishings were damaged and the floor construction was saturated with water. Sanitation and drying began immediately. The church was closed for several months, parts of the floor in the church room were replaced and the murals were restored by a conservator. The reason for the activation is unclear but may have been due to freezing of condensed water in the piping or material exhaustion in the glass bulb or the nozzle [13].
Case 2: In February 2018, an automatic high-pressure dry-pipe water mist nozzle activated for an unknown reason in a church dating from the 1600s. The system was installed in 2005. The attic has wooden beams with mineral wool insulation and below that wooden planks that make up the ceiling in the church hall. Parts of the attic floor structure were damaged with elevated moisture levels in the insulation, wooden beams and wooden planks. The wooden floor in the church hall had an elevated moisture level and visible discoloration. The floorboard in the church hall and underlying insulation had a slightly elevated moisture level. There were signs that water had run down to the foundations below the church, but this was difficult to confirm due to limited access [14]. During the site visit in autumn 2023, it was determined that the system was poorly drained. To investigate any damage to nozzles due to freezing of residual water, nozzle samples were removed for inspection, refer to Section 5.4.
Cases 3 and 4: A dry-pipe high-pressure water mist was installed in 2008 in a church dating back to at least the 1600s. On Christmas Eve 2009, an automatic nozzle in the attic activated. The plant attendants’ recalls that the activation occurred late at night. It took a while before the system could be turned off and large areas of cellulose insulation were saturated with water and had to be replaced. An art restorer conducted an inspection a couple of weeks later. There were minor marks in the ceiling fresco and the damage was considered to be of a less serious nature. No preservation procedure was required. According to an incident report from the rescue services, the second incident occurred an evening in January 2011, i.e., a little over a year later. The first unit arrived at the church after 19 min. According to the report, two nozzles in the attic activated and the report describes that there was water damage to the insulation, ceiling (frescoes) and to the church floor [15]. The response time may seem long but is not considered out of the ordinary in sparsely populated municipalities in Sweden and may have been affected by both darkness and slippery winter road conditions.
Noticeably, both system activations occurred during winter and the suspected reasons were freezing of residual water in the pipes. After these cases, the system was converted to a wet-pipe system with antifreeze. This has, however, resulted in problems with high system pressures and leakage. Nozzles and pipe connections leak frequently, sometimes only a few drops are visible, but in other cases there are larger quantities that require a bucket under individual nozzles or connections. During the site visit in autumn 2023 nozzle samples were removed to document their condition, refer to Section 5.4.
Case 5: A church where the oldest parts were built in the 1600s has a high-pressure water mist system installed in 2013 that is filled with antifreeze. An automatic nozzle installed under an eave activated in March 2018. Figure 3 shows the nozzle and here it can be seen that the top of the protective frame around the glass bulb has broken. The internal pressure in the pipe system has thus been transmitted via the glass bulb, which has resisted the pressure, to the metallic parts of the nozzle that did not. It can be noted that the thickness of the frame is at its smallest at the connection between the arms and the top. Upon activation, a fire alarm was generated. When the facility manager arrived, he found that the water flow was low, which indicates that the nozzle was partially clogged. The activation caused no major material damage.
Fig. 3
An automatic high-pressure water mist nozzle protecting the façade of a church that unintentionally activated. The nozzle is made from brass but was painted by a conservator after installation to blend into the background
Case 6: The church which was inaugurated in the 1600s has a high-pressure water mist system installed in 2011 where all parts of the pipe are filled with antifreeze. Two nozzles installed in the church attic above the altar of the choir and baptismal altar, respectively, activated without fire in August 2018. Figure 4 shows the two nozzles. For one of the nozzles, damage can be seen to one of the protective frame’s arms. However, the protective frame has not broken, it is the glass bulb that has been the weakest link. For the other nozzle, the top of the protective frame has broken and not the glass bulb.
Fig. 4
Two automatic high-pressure water mist nozzles in the attic of a church that unintentionally activated. Both nozzles are made from brass but are chrome plated
Case 7: During the renovation of a church from the early 1700s in 2011, the church regained white-painted interior walls and ceilings. In addition, new ceiling fixtures were installed as well as new cabinetry in the sacristy and a new heating system and a high-pressure water mist system was installed. In May 2013, an activation of an automatic water mist nozzle in the attic led to extensive water damage in the southern part of the church. The water damage to the building could be repaired after dismantling the inner panel and wooden floor. But the organ was completely destroyed and was replaced by a digital organ, for which it has been possible to use the old organ facade. The votive vessel as well as the ore crown in the ceiling were damaged and had to be renovated [16]. The system is partially filled with antifreeze and occasionally high pressures (150 bar) have been noted on the system’s manometer. The activation probably took place at night and was not discovered until a day or two later when the staff noticed a strange smell in the church. All the water (2,500 L) in the system’s tank had flowed out [17].
Case 8: In September 2023, an automatic high-pressure water mist nozzle in a wet-pipe system filled with antifreeze activated in the church attic. The church took on its current appearance in the early 1700s. The system was installed in 2006. As it was daytime, there were staff on site who were able to act quickly. One of the staff members ran up to the church but it took a few minutes to locate which nozzle that had activated. In addition, visitors (tourists) in the church were worried that they had caused the alarm and needed to be reassured. Shortly thereafter, an incident leader from the rescue service arrived. The water flow was localized to an automatic water mist nozzle in the attic just above the staircase. Visibility was limited, probably both by drops of water and by dust swirling around. The incident leader did not have a thermal imaging camera but judged that there was no fire and gave a go-ahead to turn off the system. It is estimated that the system was on for approximately 10 min.
During the week it had been warm weather. The outdoor temperature at a weather station nearby was a minimum of 13.4 °C and a maximum of 25.8 °C during the day. The average temperature was 18.7 °C and there was no precipitation. It is considered unlikely that the ambient temperature in the attic could have exceeded the nominal activation temperature (93 °C) of the glass bulb, since only one nozzle activated. Another more likely theory is that the glass bulb burst due to material exhaustion. During summer, system pressures of about 220 bar have been observed. As part of the project, the church was visited the week after the incident and the damage was documented, refer to Fig. 5.
Fig. 5
The attic joist where the automatic high-pressure water mist nozzle unintentionally activated. The thermal insulation was soaked and has been removed
Case 9: This church is a whitewashed stone church centrally located in one of the largest cities in Sweden. The nave, choir and sacristy were built in the early 1800s. The church has a traditional sprinkler system (dry-pipe system) that was commissioned in 2016. In March 2018, a sprinkler in the tower activated. The reason for the activation could not be explained but the 5 mm diameter glass bulb was found and was intact. The sprinkler was submitted by the installer to the sprinkler manufacturer for investigation, but the reason for the activation never received a formal answer. The water damage was limited [18].
5.3 Unintentional Activations of External Deluge Sections
Based in the interviews with the end-users, it was noted that unintentional activations of external deluge sections are more frequent than unintentional activations of automatic sprinklers or nozzles. However, the resulting water damage is significantly less, and all cases are therefore not documented in detail. Documented reasons for activations include the operating temperatures of linear heat detection cables being too low, rainwater entering electrical junction boxes, faults in fire alarm panels and mechanical damage to linear heat detection cables during lawn mowing or tarring of roofs. No intentional mechanical damage was documented, but one activation occurred in connection with copper thieves pulling down copper downpipes and lightning conductors. The thieves also tried to remove linear heat detection cable from the façade which caused an activation of the high-pressure water mist system. The incident occurred in December 2022 and the winter cold caused ice to form on the façade. After the theft, gutters and downpipes were changed to red-painted sheet metal. Figure 6 shows the façade after the activation and testing of the same system section during the site visit in autumn 2023.
Fig. 6
In a theft of primarily copper downpipes and lightning conductors, a deluge section of a high-pressure water mist system activated when the thieves also attempted to steal linear heat detection cable on the façade. The incident occurred in winter 2022, which caused ice to form on the façade (left). On the right is seen the testing of the same deluge section during the site visit in autumn 2023
5.4 High System Pressures and Leakage of Antifreeze
As many as 15 or more of the churches have high-pressure wet-pipe water mist systems with antifreeze. The antifreeze used is pre-mixed to the desired freezing point (normally − 30 °C or lower) and is a water-based salt solution. According to several facility managers, high (in some cases up to 220 bar) and varying pressures in the systems have been documented, especially during hot summer days. Antifreeze expand and increase in volume (density decreases) when heated. When antifreeze in a closed pipe is heated, the pressure increases if it has no room to expand. The majority of systems lack any form of pressure limiting equipment such as expansion chambers or pressure reducing valves.
Leakage over a longer period of time has occurred in nozzles, but also at pipe connections and at valves. It is likely that the high system pressures described above contributed to an increased probability of leakage. Due to leakage, nozzles need to be replaced on regular basis. For some of the churches, nozzles made of brass have been changed to nozzles made of stainless steel, and pressure limiting equipment has been installed. Despite this, leakage in nozzles have been documented.
Figure 7 shows two examples of automatic high-pressure water mist nozzles dismounted from wet-pipe systems that contain antifreeze. Both nozzles are made of brass. The nozzles show signs of antifreeze leakage, including salt deposits on the glass bulb and on the supports of the protective frame. Leakage through the thread connections of the micronozzles can also be observed. The green color noted can be interpreted as formation of copper acetate (which is green), that is, the metal has been covered in verdigris.
Fig. 7
Two automatic high-pressure water mist nozzles dismantled due to leakage of antifreeze. Both nozzles are made from brass, but the nozzle to the left was painted by a conservator after installation to blend into the background
It can be suspected that the internal parts of the nozzles are so clogged that the “valve” in the nozzles would not open in the event of a fire. The nozzles are constructed with an internal piston with O-ring water seals. Salt deposits and verdigris on these parts increase the friction between the piston and the internal parts of the nozzle. Figure 8 shows an automatic water mist nozzle that has been cut lengthwise. Here it can be observed that the internal parts have also been affected by the antifreeze. Clogging of micronozzles and nozzle filters can also reduce the flow through the nozzle. It is noted that water mist nozzles are fine mechanical constructions that require high water quality to function.
Fig. 8
Irritation caused by antifreeze to the internal parts of an automatic water mist nozzle. The internal piston has been removed
For a large number of churches, the leakage of antifreeze is so extensive that the facility managers have placed buckets under individual nozzles. Figure 9 shows an example from an attic along with an example of leakage from a pipe connection. In the same space there were two more buckets.
Fig. 9
A bucket positioned in a church attic to collect leakage of antifreeze from a nozzle and leakage of antifreeze through a pipe connection in the same church
As previously described, high system pressures are the likely reason for several cases with unintentional activations causing either the nozzle’s glass bulb or its metallic structural parts to burst. On two site visits, several automatic nozzles were dismounted, and their glass bulbs examined under a microscope. The outer diameter of the glass bulb is 2 mm. For almost all of the nozzles, both surface defects (pits and scratches) and microcracks on the glass bulbs were observed. Figure 10 shows glass bulbs from nozzles dismantled from a high-pressure water mist system that is presently filled with antifreeze but originally was designed as a dry-pipe system. In 2009 and 2011, respectively, unintentional activations of automatic nozzles in the particular church occurred, refer to Cases 3 and 4 previously described. It seems likely to assume that the high system pressures generated by freezing of residual water in piping and/or high pressures caused by expansion of antifreeze could have damaged the glass bulbs.
Fig. 10
Surface defects (scratches and pits) and microcracks on two glass bulbs in nozzles dismantled from a high-pressure water mist system filled with antifreeze. Photos with different degrees of magnification
Figure 11 shows two glass bulbs from nozzles dismounted from a high-pressure dry-pipe water mist system. It is believed that the system has been poorly drained. In 2018, an unintentional activation of an automatic nozzle occurred in the particular church, refer to Case 2 previously described. It seems likely to assume that the high system pressures generated by freezing of residual water in piping could have damaged the glass bulbs.
Fig. 11
Surface defects (scratches and pits) and microcracks on two glass bulbs in nozzles dismounted from a high-pressure dry-pipe water mist system
For smaller high-pressure water mist systems, nitrogen gas can be used as propellant gas or for gas-driven pump units. The gas is usually stored in gas cylinders with a pressure of 200 bars which are connected to one or more pressure vessels with water. When the system is activated, the propellant pushes out the water in the pipe system. The nitrogen gas will flow into the protected space when all the water has been driven from the pressure vessels. There are also pumps for high-pressure systems where nitrogen gas is used both to drive a piston in the pump and to atomize the water into water droplets in the nozzle. Depending on the volume of the protected space, the nitrogen gas can pose a personal safety hazard associated with the oxygen concentration in the space being reduced. When designing a system, it is therefore ensured that the oxygen concentration in the protected space does not fall below critical levels in the event of a fire or unintentional activation.
An overlooked risk is that nitrogen gas that accidentally flows out into the space that houses the pump can constitute a life-threatening scenario. Three cases were documented where this has endangered personal safety. Two cases are described in references [13, 19] and refer to the same church. The gas pump unit with its nitrogen gas cylinders is located in an approximately 10 m2 basement space under the church that is accessed via a staircase from the floor above. In the first incident, the system activated on a façade due to a technical error. However, the plant operator noted that full system pressure was not being obtained, “there was a lot of noise” and he rushed to the space to shut down the system. Because of an unknown technical error, the nitrogen gas flowed out into the space. The facility operator shut down the system and evacuated because he felt dizzy.
In the second incident, which occurred on Christmas Eve in 2010, a few years after the first incident, a pipe connection burst and the entire space was filled with water and nitrogen gas. The fire services were alerted to the scene. A fire marshal entered the church alone and fainted due to the oxygen-poor environment when approaching the space. The reason for the failure was that a pipe connection had broken. It turned out to be due to a so-called cutting ring in the pipe connection being mounted the wrong way round. After these two incidents, an oxygen deficiency detector has been installed, which alerts if the oxygen concentration drops below the normal level in the space.
The third incident was documented in another church. For this church, the gas-driven pump is located at ground level at a distance from the church and the door faces the outdoors. Due to a technical fault, gas flowed into the space. After the incident, an oxygen deficiency detector was installed here as well.
5.6 Poorly Drained System Piping
For some of the installations in the churches studied, there is a possibility of manually flushing the system pipe-work with compressed air after the annual system trip test. As the installations are using pendent nozzles, complete flushing requires a special nozzle connection. Instead of a traditional T-connection, a Y-connection is used, as shown in Fig. 12. The connection is supposed to limit the amount of stagnant water at the inlet of the nozzles. Each end of the branch lines of the system is equipped with a ball valve. This valve is opened, and the pipe is flushed with compressed air from the other end.
Fig. 12
A Y-connection used for an automatic nozzle in a high-pressure dry-pipe water mist system. The specific connection is used to facilitate complete flushing of water from the system piping using compressed air
This technical solution has been relatively successful if flushing is made monthly. In one church, it is reported that a check of nozzle inlets after air flushing found no or little water. For this particular church there have been no freezing incidents. For another church that was visited in autumn 2023 the pipework was flushed two times with compressed air during the visit. A number of nozzles were thereafter dismounted, and small amounts of water were found in the nozzle inlets.
During the visit in one church, it was observed that pipes were virtually full of water. In this particular case it was likely because regular flushing of the pipes had been overlooked, probably during several years. The plastic-wrapped one-page instruction that had been taped up in the plant building was found in a pile of binders and other documentation.
5.7 Extensive Water Delivery Times in Dry-Pipe Systems
During the site visits in autumn 2023, several cases were documented where the pressure drop resulting from the air in the pipe system being released is not sufficient to open the dry-pipe alarm valve in high-pressure water mist systems or that the water delivery time is excessive, in the order of several minutes, as compared to the desired 60 s. The function of the water mist system is thereby compromised. The problem can be attributed to the adjustment of the control valve for compressed air installed between the system’s air compressor and the pipe system. This control valve requires careful fine-tuning to function properly. The third-party system inspector confirms that this is a recurring problem. None of the systems (different makes) where the problems were documented have type-approved solutions, simply as no system component test standards where available when the installations were made. Figure 13 shows a test where a hose having a nozzle has been connected to the inspector test valve connection.
Fig. 13
The measurement of the water delivery time in a high-pressure dry-pipe water mist system, including the collection of stagnant water in the system piping. In this particular case 0.5 L of water was collected
But the site visits in autumn 2023 show that there are also problems with traditional sprinkler systems. During one of the site visits in a larger city church, no water flowed when the test valves in the attic and the tower, respectively, were opened. The problem was likely due to a non-return valve at the pump not closing. No water pressure built up in the piping system. During a site visit to another city church, an electrical fault was found during the test which caused the sprinkler pump not to start.
The experience documented above point to the importance of testing of all the system’s functions and controls during audit inspections. Unfortunately, audit inspections are often carried out without testing the system’s functions, especially for pre-action systems. In order to document the time to fire alarm and the time it takes for water to flow out through the system test valve, several people are required. They need to activate the fire alarm using artificial smoke, measure the detection time, open the test valve, hold the hose/nozzle, be prepared at the pre-action valve to be able to quickly shut off if a leak is detected, etc. In some cases, people are also desired along the pipes of the system to be able to detect water leaks.
5.8 Disconnected or Misconnected Linear Heat Detection Cables
As previously described, deluge systems with open nozzles are usually used for façades and outer roofs. These systems are divided into sections that are activated by a separate fire detection system, typically using linear heat detection cable. For one of the churches that was visited in autumn 2023, one of the façade sections did not activate when the appropriate linear heat detection cable was manually short-circuited, although a fire alarm was generated. For two of the roof sections the linear heat detection cables were disconnected. A fire alarm contractor had serviced the facility just a couple of months earlier without noticing the faults. For another church that was visited, manual short-circuit of a linear heat detection cable operated a façade section on the opposite side of the church. According to the third-party inspector, it is common that malfunctions are discovered during testing of external deluge systems. Other faults include problems with fire alarm panels, relays, and solenoid valves.
For two of the churches that were visited, parts of the linear heat detection cables were installed without thermal insulation inside the attic. Thereby, a fire that starts in the attic could result in activation of a system section on the outside of the church which reduces system operating pressure and potentially the system performance efficiency as the water flow capacity of the pump unit is not designed for multiple fires.
5.9 The Use of Stainless Steel or Galvanized Piping
All of the high-pressure mist water systems and several of the dry-pipe sprinkler systems in the study use stainless steel piping. There is no evidence of internal pipe corrosion in these installations. For three of the dry-pipe sprinkler systems installations that were visited, pipe couplings were disconnected, and it was visually confirmed that no internal pipe corrosion had occurred. These systems have been in service for about 20 years.
For sprinkler systems using internally galvanized piping, corrosion and leaks were documented, in one case less than 15 years after installation, requiring parts of system piping to be replaced. As expected, fewer problems are found for vertical parts of system piping. The fact that internally galvanized pipes do not provide sufficiently good protection against corrosion in dry-pipe and pre-action systems is currently relatively accepted [20].
5.10 Inspection, Testing and Maintenance is Burdensome
One or two facility managers are responsible for the continuous operation and supervision of the system. For one of the churches that were visited, there was only one facility manager. He described that: “It is difficult to get others to get involved”. A facility manager at another church, who was already employed in the rectory when the sprinkler system was installed, stated that “Probably no one understood that there was even a need for facility managers”.
The fact that knowledge of fire alarm and fire protection systems is limited to one or a few people makes them vulnerable. In the case of personnel changes, knowledge transfer is essential to maintain continuous operation of a fire protection system. There is at least one example where the water mist system was taken out of operation when competence has disappeared with personnel who have terminated their employment or changed positions.
Operation and maintenance are reported to be burdensome. This applies especially to smaller congregations. The actions that are required are for example the weekly control of all water and air pressure gauge readings, the water level in tanks, the correct position of all main stop valves and the automatic pump starting test. Monthly routines include for example control of the electrolyte level and density of all lead acid cells for diesel engine starter batteries and those for control panel power supplies. But the operation of the system also includes response to system fault alarms, bookings of system service and audit inspections as well as applications for funding of the maintenance costs. A facility manager expressed the following: “Our first priority is funerals. But then we must prioritize the fire protection system. In third place come tasks such as mowing the lawn and other management”. Even simple visual checks are important. A facility manager recalls a case when a valve was mistakenly closed after a service visit by the fire protection system installer and stated that: “It feels like you go and look at the same valves week after week—but whatever it is, something could have happened”.
5.11 Few Market Actors a Problem
A problem with primarily water mist systems is that the systems have components that are unique to that particular make. If a fault occurs, the facility owner cannot hire another installer to resolve it. In the national perspective, the knowledge of service and maintenance of water mist systems in particular is found in a few people at a small number of companies. So here too there is a vulnerability linked to company or personnel changes.
For sprinkler systems, system components from different manufacturers are more or less standardized. A specific component can be replaced with an equivalent component from another manufacturer. There are also more companies to appoint to procure service and maintenance.
5.12 Third-Party Control Important
The interviews and site visits show that periodic third-party audit inspections are not as common as they should be despite the fact that annual audit inspections are supposed to be conducted according to the standards. For several of the churches, there are only service agreements with fire alarm or fire sprinkler system installers. System testing that includes people with different expertise coordinated by the third-party inspector, for example that a signal from a fire alarm system actually opens the correct section valve is therefore often missed.
Facility managers consider that the audit inspection can be seen as a training day, third-party control, and an opportunity to discuss what can be improved with an impartial person who is not looking to sell any product. One facility manager said, “It is the most important day of the year for the facility managers”.
5.13 The Total Cost for Operation and Maintenance
The cost of operating and maintaining a system over time includes, among other things:
The working hours of the facility managers.
Service agreements with fire alarm and sprinkler or water mist installation companies.
Fee to the municipality for water supply connection (where applicable).
Water analyses and internal control of tanks.
Actions and material costs incurred by defects found during service visits, inspections or actions required at regular time intervals.
Replacement of batteries and sampling filters in fire alarm panels, as well as starter batteries, fuel, glycol, and engine oil for reserve power units, etc.
Lease agreement (if applicable) for nitrogen gas cylinders as well as filling, inspection, and replacement of these cylinders.
Alarm transmission costs.
Annual third-party audit inspection costs.
Calibration of oxygen deficiency detectors (if used).
External and internal costs for alarms without fire incidents and intervention in the event of a false alarm.
The cost for individual years can vary, which is why an average cost over several years is necessary to get an idea of what operation and maintenance really cost. It turned out to be difficult to obtain detailed cost information for the items listed above. Therefore, it was not possible to compare the cost of different types of systems and system solutions. Nevertheless, the general opinion by the owners of the systems is that the cost for operation and maintenance is high. Many of the parishes apply for—and receive—funding from the diocese to cover the cost and they state that this funding is absolutely necessary to be able to afford to keep the systems operating.
6 Discussion
Many of the churches use technology that was unproven in a long-term perspective when the systems were installed, e.g., the specific antifreeze and gas-driven (nitrogen) pumps. In addition, pendent nozzles have been installed in dry-pipe systems, which is contrary to accepted practice. Some of the technical solutions had simply not been used before.
The use of wet-pipe systems with antifreeze is rare in Sweden and is not covered in the sprinkler installation standards but are used in many of the described water mist systems. The antifreeze has contributed to leakage through both automatic nozzles and pipe connections. But it has also caused high system pressures in water mist systems on sizzling summer days when the antifreeze in the pipes expands. It is noted that none of the water mist systems have been designed with pressure limiting devices, which contributes to the high system pressures. It may be that the thermal expansion of the antifreeze was underestimated during system design. For several churches, water damage has occurred when automatic nozzles (or their glass bulb) burst, most likely due to high and fluctuating system pressures over time resulting in material fatigue. Additionally, it is likely that antifreeze can clog automatic water mist nozzles, water mist nozzles are fine mechanical constructions that require high water quality to function.
Freezing of residual water in dry-pipe systems has also caused unintentional activations of automatic water mist nozzles. During one of the site visits, there were liters of water left in pipes that should have been dry, as the recommended regular (monthly) flushing with compressed air was overlooked by the facility managers. But even if made correctly, interviews with facility managers confirm that it is difficult to get piping completely dry even though these churches have powerful air compressors to flush the pipes. A small amount of water may be left in the inlet of the pendent nozzles despite the Y-connection used.
Staff from one parish expressed concern about personal injury, for example during a service in the church, in case of an unintentional activation of a high-pressure water mist nozzle because the protective frame or other metallic parts of the nozzle come off. This concern may seem unwarranted and the risk of personal injury highly unlikely. Therefore, it must be seen in a larger perspective. In 2011, an 8-year-old child died in an accident where a gravestone in a cemetery overturned [21]. In addition to the fact that the incident is deeply tragic, it meant that all gravestones in the country’s cemeteries had to be checked and if required better anchored. All parishes were affected by the incident, and no one would like to experience another tragic event. The experience raises the question if the potential for personal injury from dislodged components shouldn’t be part of the testing and approval of water mist nozzles.
Three suffocation incidents were documented when nitrogen gas driving a high-pressure water pump unit was released into a confined space with the pump. Two of the incidents can be described as profoundly serious. Oxygen depletion alarms have therefore been installed to alert for abnormally low oxygen concentrations. In order to fully resolve the problem, a change from nitrogen gas to compressed air has been discussed.
For sprinkler systems, antifreeze has not been used to the same extent; dry-pipe systems are normally used. For dry-pipe systems galvanized pipes are often used but cases of internal pipe corrosion and leakage from pipes were documented. Experience shows that stainless steel pipes are significantly more resistant to internal corrosion.
For both water mist systems and sprinkler systems, several cases with long delay times were documented when the inspector’s test valve was opened in dry-pipe systems. In some cases, the delay time could be five minutes or more, in other cases a couple of minutes. This is a serious shortcoming because fire growth is very rapid, especially in attics and in tower spaces where fire spread is vertical. With a long time delay, more sprinklers than included in the hydraulic design may operate prior water is discharged, despite that that the design area should be increased for dry-pipe systems.
A consistent observation is that the facility managers have a particularly key role for ongoing supervision and maintenance. But operation and maintenance require a significant effort from church staff, technical competence and not least a great deal of self-interest. For some churches, high staff turnover has contributed to a lack of competence and supervision and maintenance has been neglected. The work steps to be conducted by the facility managers, for example weekly checks such as test runs of pumps, sometimes create anxiety among the staff. A high frequency of operational alarms is also perceived as a burden for the facility operators and is costly.
Overall, the occurrence of technical problems and high total costs of operation, maintenance, service contracts and audit inspections have contributed to the shutdown and even removal of several water mist systems. Eight cases of system shutdown and two cases of system removal were documented among the 52 churches in the study. A church warden who has been employed ever since a system was installed summarized experiences with false alarms, unnecessary alarms to the fire service and excessive costs in a truly short and concise way: “Modern crap!”.
7 Conclusion
In total, few churches in Sweden have automatic fire protection systems; this project identified 52 churches of a total 3,400 churches. The oldest of the installations was commissioned in 1996 and the newest in 2019 (both were traditional sprinkler systems). The larger city churches that were identified are typically fitted with sprinkler systems, the small- and intermediate-sized rural churches are typically (about 84% of them) fitted with water mist fire protection systems. The majority of the installations were made during the ten-year period from 2004 to 2013 in small- and intermediate-sized rural churches using high-pressure water mist systems.
In retrospect, it can be concluded that use of new and unproven technology as well as complex and poorly supervised and maintained systems has caused technical problems and excessive costs to keep the fire protection systems serviceable. Most of the installation of water mist systems was made prior the establishment of current installation standards which may explain some of the documented problems. The use of antifreeze, gas-driven pump units, flushing of piping with compressed air as well as the protection of external facades and roofs is not covered in the Swedish installation standards. The design of these features was based on the manufacturer’s instructions. Nine cases with unintentional activations of automatic nozzles or sprinklers were identified. The number of activations of automatic deluge systems is even higher (although the exact number were not documented), but these incidents lead to less water damage as the system protects façades or roofs.
In ten documented cases, water mist systems have either been taken out of service or dismantled due to technical problems and/or excessive costs.
No activations during fire were documented but based on the conditions (potential clogging of nozzles by antifreeze or ice slurry, potential blockage of piping by formation of ice, long water delivery times, disconnected or misconnected linear heat detection cables, etc.) of many of the installations it can well be questioned whether some of the systems will function in case of fire.
Acknowledgements
The project summarized in this paper is described in a report [22] in Swedish. The contribution by the reference group of the project is gratefully acknowledged.
Declarations
Conflict of interest
All authors declare that they have no conflicts of interest.
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