DESCRIPTION AND APPLICATION

The Powder Fire suppression systems are made by a stock of chemical powder quite similar to that contained in fire extinguishers. The powder interrupts the chain reaction of the flame but also the inert gas combined in it contributes to its suppression by reducing the oxygen content in all the area of its reaction.

Main applications are in the range of class B inflammable products. Typical is the protection of rooms containing liquid fuels, normally heated, and where a protection based on carbon dioxide would represent an excessive thermal shock.
For inflammable metals, the powder systems represent the only applicable solution. Another example of application of these systems is for the protection of the big frying hot plates used in industrial cooking appliances of large communities, on ships and on oil platforms.

Generally speaking, since the suppressing action of the powder is not permanent but is limited to the moment of its delivery, powder plants are apt to protect fires that can be immediately eliminated.

The planning of the pipes for powder systems is not easy because particular devices have to be adopted to avoid powder depositing along the way and a regular flow has to be maintained.

The powder systems can be twofold: those with a single release where the containing tank is directly connected with the pipe network and simple pressurisation causes its delivery, and those with several dispensers where the container is connected to a collector from where various feeding lines converge and therefore operate according to the dispenser method.

In detail, they are made of the following components:

A pressurised tank cylindrically or spherically shaped containing the chemical powder that is pressurised
through a propelling gas, normally azote;
A cluster of pressurised azote cylinders, fitted with devices for the regulation of the gas pressure;
An automatic or manual device for quick opening of the valve;
An automatic valve allowing release of the powder only after tank having reached the requested pressure;
Pipes for fluid powder;
Nozzles and conic dispensers for systems with fixed releasing points;
Hoses and releasing pistols for systems with mobile releasing points;
Pipes for the cleaning of the pipes with azote at the end of delivery.

The azote flowing from the pressure reducing valve of the cylinder is introduced in the pressurised container through a suction pipe distributing the gas into the powder which is scrambled and made fluid. The release can only take place after pressurisation of the container, otherwise the mix powder/azote risks loosing its fluidity properties and feeding becomes impossible.

The system can be operated by a special fire detection system or manually in case of need. The quick suppression of flames obtained by the use of powder ,its lack of toxicity and its non electric conductivity have developed its use in industrial installations and in fire extinguisher vehicles. The main obstacle to its diffusion is that the application is limited to well defined places where unbearable conditions for people inside occur. In addition, the powder is causing heavy dirtiness.

Furthermore, powder systems can be at total saturation or with local application.


Powder systems at total saturation

They are used only in completely sealed rooms or made such through automatic devices. The necessary quantity of powder can be calculated multiplying the net volume of the room in cubic metres by 0.616. Since the powder has no effect if applied too slowly, it is greatly important to calculate its minimum capacity (kg./s) which can be determined multiplying by 0.0020 the net volume of the room in cubic metres.

A good functioning also depends on the placement of the nozzles that must guarantee a smooth distribution of the extinguisher, on the arrest of the ventilation and on the sealing of the various openings .All this and the start of the system must operate simultaneously.


Powder systems with local application

These chemical powder systems can be divided into those having fixed release points and those with mobile release points. In the first ones the powder jets are addressed to the areas where fire is expected to take place. In the second ones jets are directly managed by fire extinguisher men at work.