Fire suppression with water mist in microbiological laboratory

One of the world’s most advanced microbiological laboratories uses high-pressure water mist as a method of fire protection. Nessie® water-hydraulic pumps from Danfoss deliver the necessary water pressure for the nozzles.

One of the world’s most advanced microbiological laboratories has just been built at the Karolinska Institute in Sweden. It was built by the Smittskyddsinstitutet (Swedish Institute for Infectious Disease Control) and is divided into four safety zones, in accordance with BSL 1 to BSL 4 (Biological Safety Level).

The requirements imposed on a BSL 4 laboratory state that rooms must be air/gastight, floors and walls must be steel panels welded together, there must be a double HEPA filter to clean the air, and all run-off water must be boiled under high pressure before it leaves the building.

Safety requirements regarding the prevention of infection during fire suppression are even more severe and stipulate the use of small quantities of water to extinguish fires, especially since run-off water must be boiled. Water mist at high pressure lives up to these requirements, the typical water consumption being around a tenth of the quantity traditional sprinklers use. Another advantage of low water consumption is that consequential water damage to the building is kept to a minimum.
 

Ultra Fog® AB, a leading company within high-pressure water mist plants, and Skandinavisk Sprinkler were given the task of protecting the laboratory against fire. The system they installed includes three PAH 63 Nessie® water-hydraulic pumps, VRH relief valves, and VDH directional valves. In the event of fire, an advanced PLC-based control system handles signals from each of the monitoring units and activates the water mist nozzles as they are needed, while sprinklers with glass bulbs are activated individually.

Nessie pumps are used because of their relatively low weight and their ability to generate uniform pressure without pressure peaks.

A fire needs oxygen, heat and flammable materials present. Typically, conventional fire-fighting equipment removes only one of these factors whereas high-pressure water mist removes oxygen and heat and thus extinguishes the fire quicker.

In the event of fire, a pump is activated and delivers water to the water mist nozzles at a pressure of 80-120 bar (1160-1740 psi). The water is transformed into a mist consisting of very small drops of less than 100 µm. When the water mist strikes the fire, the water drops evaporate very quickly, expanding to 1700 times their original size. This both expels oxygen from the air and cools down the burning materials and surrounding atmosphere. The result is fast and effective fire extinguishing.