Danfoss water-hydraulic pumps 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).
Strict safety requirements
Where organisms are concerned, the safety requirement level demanded is among other things based on their ability to spread and the availability of effective vaccines or other effective methods of treatment exist. 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 (120°C/248°F) before it leaves the building. Everyone working in such an area must wear a pressurized suit with its own air supply, and all work must be performed in microbiologically protected chambers.
Water mist at high pressure
Safety requirements regarding the prevention of infection during fire suppression are of course even more severe and stipulate the use of small quantities of water to extinguish fires, especially since, as previously mentioned, all 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 gained from low water consumption is that consequential water damage to the building is kept to a minimum.
Ultra Fog® AB, one of the leading companies 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 Danfoss 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 in groups as they are needed, while sprinklers with glass bulbs are activated individually. To make sure the system is not activated in error, fire must be detected by two independently monitoring units.
Danfoss pumps are used because of their relatively low weight and their ability to generate uniform pressure without pressure peaks. This means a constant spray range and a homogenous "spray picture". The director of Ultra Fog®, Bo Kure, is convinced that high-pressure water mist will be used to a much greater extent in the future since it gives many advantages over traditional sprinkler systems.
Facts on high-pressure water mist for fire suppression
For a fire to start there must be 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 thus transformed into a mist consisting of very small drops, ie less than 100 µm. When the water mist strikes the fire, the water drops evaporate very quickly expanding to 1700 times their original size. The expansion both expels oxygen from the air and cools down the burning materials and surrounding atmosphere. The result is very fast and particularly effective fire extinguishing.
One of the advantages of suppressing fire with high-pressure water mist is that the fire is put out very quickly with a minimum quantity of water minimizing damage to the building, furniture and fittings. Damage from heat radiation and reignition is also minimized since the scene of the fire is cooled down very much quicker than it would be by a conventional sprinkler system.