#powder fire extinguishing
What's wrong?
For comparison, the short-term action modules of IVC Technomash MPP-25 (OPAN-25) with similar characteristics were used. Their distinctive feature is the release time of 20 kg of powder — about 3 s — and the presence of a special spray nozzle for volumetric extinguishing in limited areas (<50 m2) and volumes (<80 m3).
Low-capacity (up to 10 kg of powder) pulse action modules — MPP-2.5, MPP-6 and MPP-10, are recommended by the developers for extinguishing with one 10-kilogram module up to 80 m2 in a volume of up to 250 m3 of any fires without limiting the size of the premises, fire load characteristics and the speed of automatic fire detection.
The most important thing is that such modules are advertised everywhere as volumetric powder extinguishing systems for protecting large civil, industrial and warehouse premises with a ceiling height of up to 20 m.
At the same time, the most important criterion for the reliability of powder fire extinguishing is ignored — the concentration of powder in the extinguishing volume of at least 0.5 kg/m3 and in the area of at least 1 kg/m2.
In fact, all pulse MPPs produce 15…20 times less powder, which is why they cannot extinguish not only fires outside the powder jet's range, but even in the jet itself, if there are obstacles or wood or cardboard burnt down to the coal layer, as well as heated electrical cables and containers with flammable liquids (FL), which re-ignite after the pulse flame failure.
Nevertheless, pulse MPPs are used mainly as powder installations of a reliable extinguishing method to protect any objects (!), from any fires (!), with a minimum amount of powder and, accordingly, with minimum financial costs!
«IVC Technomash» has already had to redesign cheap impulse automatic fire extinguishing systems (AUPT) for its own powder volumetric fire extinguishing systems of the «OPAN» series after unextinguished fires.
A typical example of this is the redesign and multi-million dollar redesign of the automatic fire extinguishing system of the power supply system of the «International» mine of AK «Alrosa» in 2008.
Then, after a major fire that was not extinguished by the pulse modules MPP-2.5 and MPP-5, the company «IVC Technomash» had to completely redesign the AUPT and replace the modules that failed to cope with their task with OPAN-100 modules.
With all the losses from the burned-out electrical substation, destroyed electrical cables, the costs of the useless impulse AUPT and the new protection system with OPAN-100 modules, as well as taking into account the mine downtime, the Alrosa company lost more than 70 million rubles.
A similar rework will be required at the Pushka car park in Perm, where MPP-6 impulse modules were installed in closed box parking lots, which, according to the passport, protect 25 m2 from flammable liquid fires (class B).
In reality, tests conducted by the company «IVC Tekhnomash» showed that they do not extinguish gasoline even on an area of 6.25 m2. Comparative cyclograms of extinguishing class 2B flammable liquids by the MPP-6 and MPP-25 modules are presented.
 |
 |
 |
 |
 |
The photographs show that the MPP-6's high-speed thin stream of powder, having hit the gasoline fires, does not create the necessary powder concentration around them for reliable extinguishing. And in the commercials, this pulse MPP-6 easily knocks down the flames on a large B233 fire (8 m2) with high sides in 1 second, and its passport indicates a protected area of class B — 25 m2!
The layout of the MPP-6 in one of the boxes of the Pushka parking lot is shown in Fig. 2, and in the underground parking lot under the residential high-rise building, the MPP-6 modules are installed in the open parking lot randomly between the cars (see Fig. 3) and protect 350 m2 with a total amount of powder of 36 kg (!).
What can be expected from the operation of such 6-kilogram powder modules if a fire starts under the hood of a car, and the autonomous temperature sensor USP101-E, located at a height of 3 m, will detect the fire only after a few minutes?
Extinguishing due to a small amount of powder, of course, will not occur, the fire in a well-heated closed engine compartment will develop further, despite the activation of the MPP, and after the explosion of the gas tank, it will spread to neighboring boxes and cars.
In Moscow in 2010 on Akademika Volgina Street, such a fire, unextinguished in one box, led to the destruction of the entire ground parking lot with an area of 1500 m2. In December 2008, a similar fire in the parking lot under a 20-story apartment building in Alma-Ata (Kazakhstan) destroyed cars, spread to the apartments on the first floor, led to complete smoke filling of the building and the evacuation of all residents with serious consequences.
Things could get even worse at night if the parking lot is located under a high-rise residential building and one of the cars “accidentally ends up with a TNT block” (this is a problem for the Ministry of Internal Affairs and the FSB).
Major human casualties cannot be avoided, since the explosion and rapid spread of fire to dozens of neighboring cars and further to the residential complex cannot be stopped by any pulse or water installations.
What is needed here is a reliable, fast-acting, explosion-proof powder system of volumetric fire extinguishing, similar to those used at explosive oil and gas pumping stations, where the main criterion for reliable extinguishing is the accelerated supply of a sufficient amount of powder per unit of volume and area within a few minutes after a gas explosion.
An option for reliable volumetric powder extinguishing with the OPAN-25 module (20 kg of powder) of a vehicle in a 70 m3 box is shown in Fig. 4, and in a large room with OPAN-100 modules in Fig. 6.
Another aspect of the unreliable and dangerous for humans use of pulse MPP-6 in large warehouses should be considered.
With a large clutter of these objects and a long process of detecting a fire by sensors, for example, inside a stack of cardboard boxes covered with other equipment, the operation of pulse modules will not give a positive result: the fire will develop further.
Moreover, burning cardboard containers not secured to shelves, glass containers with flammable and combustible liquids, aerosol perfume cans with propane when hit by a powerful jet of powder become an additional source of fire development.
Unauthorized activation of pulse modules is extremely dangerous.
The reason for this may be electrostatic interference from lightning strikes and power surges in cheap, low-ampere systems for starting pulse fire extinguishing installations, which is the main scourge of their use.
However, their main disadvantage, along with the damaging effect on equipment and humans, is the impossibility of creating a sufficient concentration of powder at any point in the room for any length of time during volumetric extinguishing, which is a prerequisite for volumetric powder extinguishing of fires in blind “pockets”.
To eliminate this drawback, large facilities try to hang a huge number of low-capacity pulse modules on the ceiling, and since a “dead” powder-free zone is formed near the modules themselves, the upper volumes, for example, the upper shelves of a high warehouse, have to be shot through with horizontal streams of additional modules, which also have their own “dead” zones, etc.
Similar horizontal shootings should be organized in the area of the lower shelves, since from a height of 8-16 m only a small part of the powder will fall on them, which did not have time to settle on the side surfaces of high racks, and due to the loss of mass and speed of the powder at such a distance, the effect of impulse flame breakdown at the lower sources of fire will be zero.
Thus, the entire warehouse must be hung on all sides with numerous low-capacity modules.
 |
 |
 |
 |
 |
 |
 |
As a result, large cluttered objects are easier and more reliably protected by traditional modules with a capacity of 25, 50, 100 or more liters, both through pipe wiring and by free release of powder locally or throughout the entire volume, for example, by the method of volumetric aerosol-powder extinguishing patented by IVC Technomash using OPAN-50, OPAN-100 and OPAN-25 modules through Laval acceleration nozzles by feeding powder into the upper volumes of high rooms and additionally by horizontally shooting powder into the lower volumes through sprayers installed at different levels from floor.
Similar schemes for protecting large objects from local volumetric fires are practiced by the companies «NTK Plamya» and «Kalancha» (gas-powder method of volumetric extinguishing).
_________________________________
S. Yu. Serebrennikov,
director of the ITC «Tekhnomash», Doctor of Engineering Sciences,
professor, Perm