VdS-Schadenverhuetung Technische Pruefstelle

Part 1: History of the sprinkler

From cotton thread to glass ampoules

Today, sprinkler systems are an important component in numerous fire protection concepts. Next year, sprinkler technology celebrates its 150th anniversary - we take a look at its history.

Text: Hans Altmeyer, VdS Schadenverhütung GmbH

In the second half of the 19th century, several developments came together that made new approaches to fire protection necessary. On the one hand, industrialization led to the emergence of large commercial enterprises with a high concentration of people and material assets in a small space. Secondly, increasing electrification brought with it new sources of danger.

This situation initially led to the first automatic extinguishing systems being installed in US weaving mills. Water pipes ran through the production rooms and were provided with openings at certain intervals. The openings were closed with lids that were held in place by cotton threads. If a fire broke out, the threads burned through and released the openings - the extinguishing water flowed. This concept had its weaknesses: The cotton threads had to be reached by the flames for them to burn through, so they often only triggered when the rooms were already fully ablaze. It was also difficult to adapt the triggering characteristics of the extinguishing devices to the conditions in the factory. And finally, cotton could rot and unintentionally release the extinguishing water.

The American industrialist Henry S. Parmelee (1846-1902), who produced pianos and was therefore active in an industry in which large quantities of wood were processed and represented a considerable fire load and in which metal also had to be processed regularly, which created a constantly present source of ignition due to flying sparks, also recognized these shortcomings.

Parmelee therefore developed a design in which the outlets of the pipes were released by melting a metal alloy that liquefied at a temperature of 150 to 200 °F, i.e. around 65 to 93 °C. This offered clear advantages. This offered clear advantages. Depending on the composition of the fusible link, the release temperature could be preselected quite easily and adapted to the operating conditions. In addition, the mechanism did not have to be reached by flames in order to trigger.

Parmelee also took into account problems that became apparent when looking at the entire system. For example, the installation of non-heat-conducting elements in the system ensured that the cooling from the now flowing and no longer stagnant water could prevent neighboring sprinklers from being triggered because the fusible link there remained at a lower temperature level. Parmelee also provided for the triggering of an acoustic signal.

On August 11, 1874, the US patent for Parmelee's invention was granted under the number 154,076 - the principle of the modern sprinkler system was born.

Parmelee was the first to equip the building of his Mathushek Piano Manufacturing Co. with sprinklers, and others followed. However, the spread of sprinklers was finally spurred on by US insurers, who soon recognized the benefits of the innovative technology and pushed for the installation of such systems. In 1881, insurance companies in Great Britain also began to reward the installation of sprinkler systems with discounts on insurance premiums.

In Germany, the technology began to establish itself in 1884 - initially in mills and textile processing companies. Known in this country under the term “fire extinguishing shower”, sprinklers became widespread, as they did in the Anglo-American world, especially in large industrial plants.

Insurance companies were also a driving force here. In 1900, the Association of German Private Fire Insurance Companies commissioned Hugo Junkers, then Professor of Thermodynamics at the Royal Aachen University of Technology, to draw up an expert report on the various sprinkler systems in use at the time. Aachener und Münchener Feuerversicherung was also active in researching the technology, sending its chief inspector Dr.-Ing. Hofferichter to Great Britain to study the practical use of sprinkler systems on site - in 1901 he published his report “Über automatische Feuerlöschbrausen” (On automatic fire sprinklers), which was groundbreaking for the insurance companies involved in the subject. With the backing of the insurers, the triumphant advance of sprinkler technology was unstoppable: While around 50 sprinkler systems were installed in Germany around 1900, by 1909 there were already 80 and by 1912 200 systems.

As the number of sprinkler systems grew, so did the realization that sprinklers needed to be inspected and maintained. This task was initially in the hands of six sprinkler manufacturers, who were obliged by the fire insurance companies to carry out regular inspections of their systems. This meant that the manufacturers were responsible for monitoring their own products - which could only be a temporary solution at best.

At its general meeting in 1904, the Association of German Private Fire Insurance Companies therefore decided to establish a sprinkler commission. The commission, based in Berlin, was to develop manufacturer-independent standards for the design, installation, acceptance and regular testing of sprinkler systems.

This mandate was fulfilled with corresponding regulations published on 01.04.1906. At the same time, the insurers set general discount rates that were granted on insurance premiums when a sprinkler system was installed.

In the same year, a sprinkler laboratory was set up at the Royal Technical University in Aachen, where approval tests for sprinklers were carried out in accordance with the Commission's guidelines.

Soon afterwards, in 1908, the “Regulations for the Sprinkler Monitoring Service” were published, and at the same time the Sprinkler Monitoring Center of the private fire insurers was founded - the direct predecessor of the Technical Inspection Authority at VdS. We will take a closer look at its role in the use and spread of sprinkler systems in the next episode.

However, the technical development of the sprinklers themselves did not stand still either. Parmelee had created a well thought-out functional principle, but the sprinklers still offered room for detailed technical improvements. This was recognized by Frederick Grinnell (1836-1905), who was already active in the production of fire protection technology. He acquired a license for Parmelee's design and then improved the triggering device and the distribution of water through the individual sprinkler heads, among other things.

However, he achieved his greatest success by replacing the fusible link device with a glass ampoule. The ampoule contained a liquid based on glycerine, which burst at a defined temperature due to the rising internal pressure, thus releasing the outlet for the extinguishing water. Sprinkler heads still work on this principle today.

Unlike the fusible link, the triggering temperature is not defined by the composition of the liquid, but by the size of the air bubble in the ampoule. Unlike liquids, air can be compressed. As the temperature rises, the air bubble is compressed until the required pressure is higher than the bursting pressure, which causes the ampoule to burst. The smaller the air bubble, the sooner this situation is reached.

In this way, the triggering temperatures for sprinklers can be adapted quite precisely to the usual ambient conditions in the respective application scenario and heating within a certain fluctuation range does not lead to false triggering. As a rule, sprinklers are only triggered when the temperature at the ampoule is around 30 °C above the maximum temperature that can be expected under normal operating conditions. To avoid false triggering during installation, the liquid in the ampoule is colored differently depending on the triggering temperature.

System technology has also developed further. Today, so-called dry systems allow sprinklers to be used in areas at risk of frost. The supply pipes to the sprinkler heads are filled with compressed air. When a sprinkler is triggered, the system detects the drop in pressure and only then fills the pipes with water.

In their modern form, sprinklers were soon able to conquer other areas of application thanks to the very flexible installation options. Initially, sprinklers were mainly used in industrial plants, but over time public buildings such as hospitals, nursing homes and shopping centers were added.

Sometimes it was major fire disasters that made the need for a sprinkler system obvious. For example, the devastating fire at Düsseldorf Airport on April 11, 1996, which claimed 17 lives, led to the major German airports subsequently being equipped with sprinkler systems. Similarly in the Netherlands, when a prison in Schiphol near Rotterdam caught fire on October 27, 2005, killing 11 people, many Dutch prisons were subsequently fitted with sprinkler systems.

Nowadays, however, building regulations often ensure the installation of extinguishing systems - and not least a sense of responsibility and common sense on the part of building owners.