New challenges call for innovative solutions
Since its development in the 19th century, the sprinkler has had an unprecedented career as an element of fire protection in the 20th century. For many buildings, the sprinkler became an important element of personal protection and often the basis for risk transfer by insurers.
In the 21st century, water extinguishing systems are part of many new construction projects. For example, buildings over 22 m high generally have to be equipped with appropriate systems. Particularly in high-rise buildings, where the fire department can no longer reach the higher floors from the outside with their ladders, sprinkler systems can be crucial lifesavers. Fires are detected early and controlled until the fire department has reached the source of the fire.
Of course, structural fire protection also makes a decisive contribution to achieving the protection objective. Due to the central importance for the safety of high-rise buildings, there are special requirements for the availability of the systems in the technical regulations. The failure of a pump must not affect the effectiveness of the system any more than the failure of the power supply. Redundant pumps, control cabinets and energy sources ensure that the systems are available 365 days a year wherever possible.
But the requirements go even further: in high-rise buildings over 60 m high, each floor must be fed from two different sides so that the failure of a riser (e.g. during maintenance or renovation) has no effect on system availability. It must also be possible to maintain the alarm valves in such a way that the water supply to the sprinklers is guaranteed.
The industrial sector has probably seen the greatest change in sprinkler systems. Whereas in the 19th century, storage was almost exclusively on the floor, later on more and more was built upwards. Racking systems found their way into logistics and cases of damage showed that classic sprinkler protection on the ceiling alone was no longer sufficient to fight fires.
Based on fire tests, VdS introduced the so-called rack sprinklers in 1971. In principle, shelving systems could then be built to any height if sprinklers were arranged in the shelving at specified, regular intervals. Today, there are racking systems over 40 m high that can still be sprinklered according to the same principle as in the early 1970s.
However, development did not stand still. Space was becoming more and more precious and so the racking systems were increasingly optimized. Initially, the traffic areas between the racks were wider than the storage blocks themselves so that the forklift trucks had room to maneuver. With increasing optimization and automation, the storage area became larger and larger. In automated small parts warehouses or shuttle racks, the aisles can shrink to less than one meter wide.
The development of racking systems together with the rapid spread of plastic containers as load carriers posed enormous challenges for sprinkler systems. While the horizontal distance between sprinklers in the first racking systems could still be extended to over 3 m, modern automatic small parts warehouses sometimes require distances of less than one meter to ensure effective firefighting. And not only that, additional rows of sprinklers are sometimes required on the sides of the aisles (so-called face sprinklers). Modern storage systems can require the use of several thousand or even over ten thousand sprinkler heads.
However, the densification of warehouses has not stopped here. Currently, compact warehouses are being built in which there are no aisles at all. The systems are operated by robots either from above or from below. As it is practically impossible to install sprinkler heads inside the blocks, these systems pose completely new challenges for sprinkler technology. Fire tests have shown that sprinkler systems are perfectly capable of fighting fires in these condensed arrangements. The fire department, which is called to carry out the final extinguishing or at least check the source of the fire, faces enormous challenges in removing the individual storage containers. With regard to business interruption and smoke damage, these developments are viewed very critically by many insurers.[1]
[1] Please click here for the GDV source reference (german)
In an international comparison, the spread of sprinklers in Germany could well be greater. There are countries in Europe where significantly more sprinklers are installed. Take Norway, for example, where new residential buildings with more than two floors are sprinklered, in Scotland and Wales retirement homes are sprinklered and in Sweden all hospitals are sprinklered.[2] Unfortunately, people die in social facilities every year (2023: 193 fires with 305 injuries and 28 deaths[3]) and yet there are no regulations to equip hospitals or care facilities with sprinkler systems.
[2] Please click here for the source reference (german).
[3] Please click here for the source reference (german).
ESFR sprinkler
In the 1980s, a new type of sprinkler was developed in the USA that has become an integral part of today's logistics world: the ESFR sprinkler (ESFR = Early Suppression Fast Response) can suppress a fire at an early stage by triggering very quickly. The first ESFR sprinkler had a K-factor of 14.0 GPM/√psi (gallons per minute by root of pressure in psi; metric approx. K-200; for better readability, metric K-factors without units are used below).[4] The K-factor was thus twice as large as that of the currently common “control mode sprinklers” with K-factors of 80 or 115.
With these sprinkler types, it was now possible to protect significantly greater storage heights without having to install rack sprinklers. On the other hand, the requirements for the building and the warehouse configuration are very high. It is also said that with ESFR sprinkler systems, the building must be planned around the sprinkler system. Ceiling slopes, spray obstructions and SHEVS are just a few of the points that need to be taken into account. The storage itself must also meet important criteria such as the formation of shafts between loading units.
In the USA in particular, this technology has been researched and tested for decades to determine which configurations are still manageable and which are not. Tests have also shown that concepts that were considered effective do not work after all and have had to be withdrawn. Constantly changing boundary parameters play a major role here. For example, cardboard boxes made from waste paper - which are generally easy to protect with sprinklers - now contain significantly more plastic than a few decades ago due to recycling processes. This is why existing concepts have to be put to the test time and again.
Since the 1980s, there has been constant further development and today the largest ESFR sprinklers have a K-factor of 480, which means that when a sprinkler opens and, for example, a water pressure of 9 bar flows through it, the sprinkler discharges approx. 1,500 l/min. With this type of sprinkler, it is possible to store plastics packed in cardboard boxes over 15 m high and then protect them with sprinklers on the ceiling only.
[4]In Europe, the K-factor is given metrically in (l/min)/√bar(liters per minute divided by the square root of pressure in bar). The conversion factor is approx. 14.4, so the imperial K-factor 14.0 in Europe is approximately K-200. Even with water rates in gallons per minute or water pressures in “gallons per square foot per minute”, the conversion of the different units is often laborious. The hope remains that in less than 150 more years the metric system will be used uniformly worldwide.
Concepts for the water supply
The development of larger sprinklers with higher water pressures also had a direct influence on the water supply to the systems. In the early sprinkler systems, the water was taken from an elevated tank - the pressure at the sprinkler was therefore created solely by the geodetic height of the water column. Later, the systems were also connected directly to the public water supply network. This is still common practice in many countries around the world today, especially for small systems.
In Germany, this form of water supply is not permitted for hygienic reasons. This is certainly one of the reasons why sprinkler systems have not been widely used in residential buildings and care facilities in Germany. In Germany, one or more tanks with one or more pumps are generally required for the water supply.
In the sprinkler guideline Form 155 from 1968, there was a requirement for the sprinkler pump to be able to deliver at least 3,000 l/min at 50 m WS (meters of water column). Today, systems are installed where the pump must be able to deliver more than 15,000 l/min.
To achieve these water rates, two pumps are often operated in parallel. The power requirement of the pumps can be over 500 kW. Multiplied by the operating time of 60 minutes, 90 minutes or even more, this results in systems for which more than 1,000 m3 of water must be stored, possibly redundantly in two tanks, where the pump delivery rate must be more than 15,000 l/min.
The K factor describes the water discharge rate of a sprinkler, or more precisely: the amount of water that is discharged by the sprinkler per minute at one bar of water pressure. In the metric system, K 80 means that the sprinkler delivers 80 liters of water per minute at a pressure of 1 bar. At a water pressure of 2 bar it is 113 liters per minute, at 0.5 bar it is only 57 liters/minute. The discharge (Q) can be calculated according to the formula Q = K x √p for any pressure (p). The K factor is a design characteristic of the sprinkler. Common sprinklers, for example, have K values of 57, 80 or 115, ESFR sprinklers up to K 480, sprinklers in high-pressure water mist systems sometimes below K 2.0.
Halon ban and water mist
A completely opposite development has taken place in the area of very small droplets. On March 2, 1989, the EU decided to ban the climate-damaging CFC gases (chlorofluorocarbons) by the end of the 20th century. As a result, the Federal Republic of Germany issued the CFC-Halon Prohibition Ordinance on August 1, 1991 and completed the phase-out of fully halogenated chlorofluorocarbons by the end of 1994. Before this ban, gas extinguishing systems using halon as an extinguishing agent were very popular in all areas where water was unsuitable as an extinguishing agent.
Alternatives were sought to replace the halon fire extinguishing systems. In the case of water extinguishing systems, this led to the further development of water misting technology, which had been known since the early 1930s. Unlike ESFR sprinklers, high-pressure water mist (HPWM) works with very small K-factors (down to less than 2.0 metric!) but very high pressures (80 bar and more at the sprinkler). In the meantime, systems have proven their effectiveness for a wide variety of applications (e.g. garages, hotels, offices, machine rooms, cable tunnels, paint shops, transformers and many more) and are used there. According to current knowledge, however, this technology is not suitable for large storage and logistics areas.
When stockpiling 1,000 m3 of water or more, the question arises as to whether this is still justifiable in terms of sustainability. Several factors must be taken into account here. Firstly, the water for sprinkler systems only needs to be filled into the storage tanks once and can then remain there for many years or decades.
The regulations now allow regular checks to be carried out by divers or diving robots. By activating sprinklers early and thus limiting the spread of fire, a major contribution is made to environmental protection.
FM Global already carried out studies in 2010[5] and showed in other publications that the water requirement in sprinklered buildings is 50 to 91 % lower than if only manual firefighting is carried out by the fire department.
Greenhouse gas emissions can be reduced by up to 97 %. In addition, the formation of toxic substances is significantly reduced. Further information can be found in publications by HOYER Brandschutz GmbH[6] and the bvfa[7].
[5] Source: FM Global Research Technical report – „Environmental Impact of Automatic Fire Sprinklers“ (March 2010) by Christopher J. Wieczorek, Benjamin Ditch & Robert G. Bill, Jr.
[6] Please click here for the source reference (german).
[7] Please click here for the source reference (german).
The challenge of flammable liquids
New challenges are constantly arising as a result of further developments in the industry. Another example is flammable liquids, which are transported and stored worldwide in large plastic containers (IBCs - Intermediate Bulk Containers), usually with a capacity of 1,000 liters.
The entire contents of these containers can be released suddenly due to mechanical damage or fire, resulting in pools of liquid covering several hundred square meters. If this area catches fire, it is almost impossible to fight the fire using water extinguishing systems.
In 2020, extensive fire tests were carried out with the support of VdS in order to find a protection concept for this storage. The approach is based, on the one hand, on liquid barriers (so-called FuelStops), which prevent the formation of large pools of liquid, and on the other hand, fast-acting sprinklers are installed in such a way that they quickly cover the area between shelves with a layer of foam. Certification of this protection concept[8] has solved another problem.
[8]Please click here for the source reference (german).
As shown, sprinkler technology has become an integral part of the world of fire protection. Time and again, innovative developments are presented which then establish themselves - or disappear from the market again. Only through the - sometimes very cost-intensive - research of insurance companies, manufacturers and installers can solutions be found for new challenges.
But even if standards are regularly developed further through research and testing, innovations in the fields of logistics, architecture, production and chemistry are increasing exponentially (at least it feels that way). Visits to trade fairs repeatedly reveal innovations for which no fire protection solutions can initially be found in the established standards and norms. A great deal of engineering work is then required at the desk and in the fire house in order to develop new concepts for system-related fire protection.
Sprinkler systems with negative pressure in the pipe (so-called vacuum sprinklers), electronically triggered sprinklers, speed-controlled pumps and fluorine-free foaming agents are just some of the buzzwords that make it clear that sprinkler technology is still being further developed even after 150 years.