DESCRIPTION AND APPLICATION

Fire extinguishers are nowadays a common sight in all premises where work or life is carried out as well as in public transport. These appliances, also called containers with an extinguishing agent that can be thrown towards a fire through a pressure gauge, can be of a portable or wheeled type and are used to fight a "start" of fire.

The Ministerial decrees D.M. 20.12. 1982 and 6.3.1992 state that fire extinguishers, in order to be put in use must undergo a technical and administrative procedure (homologation) designed by the Interior Ministry to certify their compliance to the norm.
Therefore, all extinguishers on sale must be homologated according to the above procedure.

The decree D.M. 7.1.2005 published by the Gazzetta Ufficiale della Repubblica Italiana number 28 of 4.2.2005 indicates the rules for the classification and homologation of portable extinguishers as shown in the norm EN3/7:2004.

The decree is made of 12 articles and it is in force since 4.6.2005.

Article 11) "Norme transitorie" states that commercialisation of portable extinguishers homologated according D.M.20.12.82 is allowed for a period no longer than 18 months starting from the date of the application of the decree, therefore until 4.2.2007.
The decree also states that portable fire extinguishers homologated according to decree D.M. of 20.12.82 can be used for 18 months starting from the date of production punched on all portable extinguishers.


Extinguishers with dry chemical powder

The extinguishing agent in this case is a dry powder which is launched towards the fire thanks to a pressurised gas contained in a small cartridge internal or external to the fire extinguisher or in the upper part of it.
The most used powders, those based on ammonium phosphate, are apt for suppression of fires of class A, therefore they have a polyvalent use. Other powders are used for suppression of class D fires as those of metals or celluloid.
All dry powders are treated with special additives so as to avoid clots of humidity.
Pressurisation is obtained with azote.


Extinguishers with carbon dioxide

Carbon dioxide is stocked on a liquid state in special cylinders. For its use, a pressure gauge throws the CO2 on a liquid state into the delivery cone where a rapid evaporation occurs together with a strong cooling action. Then carbon dioxide becomes solid taking the form of small particles similar to snow flakes.
The suppression action of CO2 is through a suffocation and cooling process reducing the oxygen quantity at a level where combustion can no longer take place.
An essential condition for a successful fire fighting is that CO2 be concentrated in the area of fire; it is therefore imperative the absence of ventilation. Therefore the effect at the open air is greatly diminished, especially in a windy area. The action caused by snow flakes only is limited and the fire extinguisher is not particularly recommended for class A fires (wood, paper etc).
The advantage is that no corrosive action takes place nor any trace is left after a short period. This is the reason why it is widely used on electric or electronic equipment.


Water fire extinguishers

Pure water is used as extinguishing agent. The old type, now disappeared, was made of a cylinder containing a solution of sodium bicarbonate with water and with a sulphuric acid phial. When in use, the rupture of the phial produces a chemical reaction between the two products and subsequent formation of pressurised carbon dioxide in the upper part of the cylinder. The modern water extinguishers are of the pressurised type containing water only that is released by a pressure gauge fitted into a special cartridge internal or external or placed in the upper part of the cylinder.
Water fire extinguishers are used for class A fires, especially cellulose, wood, paper leaving coal residues. They can have a full or fractional jet, the latter being preferable when a long throw is not needed for its stronger action and reduced risk of damage to electrical equipment at high voltage.


Foam extinguishers

The extinguishing foam is an aqueous film mix of water or CO2 and special foam agents. The resulting foam is very light and can float above all inflammable liquids so as to form a continuous sealing layer between the liquid and the air above. When oxygen is reduced, the vapours produced by fire are no longer burning so fire is suffocated. The modern extinguishers are of the pressurised type. A certain amount of foam is filled into the cylinder and is then released at a certain speed through a grip trigger pistol.
The foam extinguishers are mainly based on the suffocation principle and only marginally on the cooling effect and are mainly used for class B fires, viz. those of inflammable liquids.
Alcohols and other inflammable liquids tend to dissolve ordinary foams and in this case alcohol resistant foams have to be used.

As far as the installation is concerned, all fire extinguishers must be reached through a route with no obstacles and with a max. distance which before was of 15 metres and at present is fixed at 30 metres by the D.M. 10.03.1998.
Obviously when various obstacles exist (as in the case of supermarkets) the 30 metres distance is no longer acceptable. Therefore the location of fire extinguishers is also connected with the location of the staff who presumably is asked to use them.
Taking into consideration that possible users can not be athletically fit, the installation of 6 Kg. extinguishers is recommended as that they can be used without much effort. The fire extinguisher is considered portable according to the norm if its total weight does not exceed 20 Kg.

The fire extinguisher must be easily visible and must not create encumbrance on the way of people and vehicles. It must be wall bracketed and its handle must be no higher than 150 cm. from the ground. In the same place a panel must installed so that it can be easily seen. These signs must comply with the decree D.Lgs. 14 .08.1996 n. 493 which takes into account the norm on security signs 92/58/CEE.
Furthermore, fire extinguishers must be fitted inside and outside the area to be protected and in any case near accessible points and points to be protected.

The installation of carbon dioxide extinguishers must occur in wide premises in order to avoid risks for people as a result of the oxygen reduction. It is important to warn the personnel that carbon dioxide extinguishers can represent a danger as they can provoke burns caused by the cooling effect (-78°) during the release time.

As far as dry powder extinguishers, the only precaution is to create ventilation after their use.

In case of use on electric appliances, only extinguishers that have overcome the dielectric test can be utilised.

In the various activities subject to fire protection there are indications about the type of extinguisher to be used, whereas for other activities not requiring protection, reference is made to D.M. 10.03.1998.
The decree D.M. 10.03.1998 is valid for all activities where personnel is present and requires the appreciation of fire hazards which can be classifies as low, medium, high.

On the basis of this classification, the same decree at comma V art.5.2 reports the following Table A.



In addition, the following general rules are indicated:

No less than one fire extinguisher for each floor;
The choice must be dictated by the evaluation of fire hazard (class of fire);
The distance to reach the extinguisher by one person must not exceed 30 metres.

The choice of the extinguisher is based on its main characteristics, viz. its fire fighting capacity and the nature of the extinguishing agent. Also the total capacity and its total weight as well as its utilisation under pressure must be taken into consideration.

The fire fighting capacity is the official classification of the extinguisher. It provides the list of the kind of fire to be fought and their extension. It is represented by a logo with letters (A,B,C,) and one/two digit numbers. Letters represent the classes of fire, numbers the relevant types of extinguishers.

The bigger the numbers the best fighting effect apply.

Table C - Classes of fire and best extinguishers


To all the above letters behaviours dictated by physical and chemical properties correspond. The material part under fire has always a gaseous component according to its properties, so successful fire suppression depends on the various types of extinguishers.

Table B - Classes of fire and performance requested by the extinguishers