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HISTORY

The first known (portable) fire extinguisher was patented in 1723 by the chemist Ambrose Godfrey. It consisted of a sort of barrel filled with extinguishing liquid with a pewter container filled with pyrical dust. An ignition system caused the dust to explode, thus spreading the solution. There is news of its use, as the Bradley's Weekly Messenger of November 7, 1729, spoke of its effectiveness in extinguishing a fire in London. The “modern” fire extinguisher was intented by the British captain George William Manby in 1818; it was a 3-gallon copper tank containing an aqueous solution of potassium carbonate, pressutized with compressed air. The first "soda-acid" fire extinguisher was patented in 1866 by the Frenchman Francois Carlier; mixing an aqueous solution of sodium carbonate with tartaric acid, obtaining foam and gaseous carbon dioxide, used as a propellant. An other “soda-acid” fire extinguisher was patented in United States in 1881 by Almon M. Granger, in this case he used the reaction between an aqueous solution of sodium carbonate and a sulforic acid. A glass vial containing the acid was suspended in the extinguisher containing sodium carbonate, the activation of the extinguisher could be done in two ways, in the first case the vial was broken, in the second a partition that normally divided the acid was removed from the carbonate. In both cases, carbon dioxide which acts as an ejection gas was produced. The auxiliary pressure fire extinguisher was invented in 1881 by the English company Read & Campbell, using water or aqueous solutions. Later, they developed the "Petrolex" for automotive use. The fire extinguisher with chemical foam was intented in 1904 by Aleksander Loran in Russia, based on the previous invention of fire-fightinig foam: Loran used it to turn off a tank of naphtha: while resembling to the sodium-acid models, the foam produced was of greater resistance. The main tank included an aqueous solution of sodium carbonate while that inside one of aluminium sulphate. Mixing the two solutions (usually happened by turning the tank upside down) the two liquids reacted to from a foam and carbon dioxide in the gaseous phase, which expelled foam. Subsequently additives (such as liquorice extracts) were used as stabilizers, but the foam was formed solely by the reaction of the aforementioned components. In the 1910, the Pyrene Manufacxtoring Company of Delaware filed a patent for a Tetra system (carbon tetrachloride - Halon 104). Vaporizing the liquid on the flame extinguished it by suffocation. In 1911, they patented a small portable fire extinguisher with the same extinguishing agent set up by a small brass tank with a hand pump with a hand pump to expel the liquid towards the fire. The capacities were 1.1 liters or 0.6 liters but were also available up to 9 liters. The container was not pressurized, and therefore could easily be recharged. Another type of fire extinguisher a “tetra” was the so-called Fire grenade. A glass sphere filled with carbon tetrachloride, to be thrown at the base of the flame (the former used saline solutions, but the "tetra" proved to be more effective). The “tetra” was suitable to fires of electrical systems and flammable liquids. Carbon tetrachloride fire extinguishers were withdrawn in the 1950s due to toxicity, exposure to high concentrations damages the nervous system and internal organs; moreover, exposed to high temperatures it can convert into the toxic gas phosgene. In the 40s was invented the Hulan 11 liquid (bromochloromethane - bromomethane - methyl bromide) for use in planes. More efficient than carbon tetrachloride, it was used until at 1969. Methyl bromide was recognized as an extinguishing agent in the 1920s and was used mainly in Europe; highly toxic, it was finally banned in the 60s. The carbon dioxide (CO2) fire extinguisher was introduced by Walter Kidde Company in 1924 on requesto from Bell Telephone for a non-conductive fluid that can be used on fires in telephone exchanges. It consisted in a cylinder containing 7.5 pound of CO2 with a screw valve and hose in brass cloth insulated with cotton, ending with a sort of funnel nozzle. In 1228, DuGas (subsequently acquired by Ansul) presented an “auxiliary pressure” powder fire extinguisher loaded with sodium bicarbonate, with special additives to make it sliding and resistant to moisture. The operator had to rotate a valve over fire extinguisher to puncture the cartridge and then operate a lever at the end of the house to release the chemical powder. This was thew first extinguisher suitable for fire liquids or gases of generous extension, but remained of limited use until the ‘50s, the entered the market for house hold extenguisher. Also in the 50s ABC powder was developed, the Super-K in the early 60s and Purple-K ìwas developed bt the Amerincan Navy in the laste 60s. Also in the 50s the Halon 1211 (BCF) was developed, while the Halon 1301 (BTM) was synthesized by DuPont de Nemours for the American army in 1954. The fluobrene (Halon 2402) was produced for the first time in 1969 at the Montecatini factory in Porto Marghera, and was tested in the Monza and Hockenheim car circuits. During the tragic accident at Monza in 1978 the Squadra Corse of the CEA extinguishers intervened saving the lives of numerous pilots.

DESCRIPTION

Although fire has always been considered a potential enemy, and in ancient times it has been worked to reduce fire risk and to make fire extinguishing, the fire extinguisher is a fairly recent product, whose invention dates back to 1816 (George William Manby), but whose diffusion is much more recent, starting from the 30s of twentieth. Previously there were portable small extinguishing systems, consisting in practice of hand pumps capable of sending jets of water at a distance, but these were not very effective means, as the power supplied by an adult, of the order of 300 W, did not allow the effective use of water, the only available agent. The development of different extinguishing agents and the construction of tanks light and resistant to high pressures, which allowed the launch of the extinguishing agent at a great distance by compressed gas, allowed the realization of the extinguishers as we know them today. The fire extinguisher represent an essential element for the security of any building or motor vehicle. A perfectly efficient fire extinguisher can result more useful than all the means present in a Fire Fighter Command: if used promptly and correctly on a fire principle, within the limits of its extinguishing capacity, allows to contain material damage and protect the safety of person. Countless tragedies could be avoided with the timely use of a fire extinguisher. Where the fire prevention legislation is lacking, the common sense of the owners or users of buildings and vehicles must lead to the purchase of suitable fire extinguishers and to their periodical maintenance through specialized firms, negligible expenses when compared with the amount of minimum damage that could occur in case of fire. The public services of Antifire and Aid do not guarantee the timeliness of their intervention, subject to unpredictable events of force major, while the fire-fighting equipment supplied with the various activities constitute protection tools immediately available and usable by the citizen.

CONSTRUCTION

A fire extenguisher is usually consists of the following components:

One or more tanks, suitable to contain the extinguishing agent, the propellant or both;
A valve, designed to intercept and / or regulate the flow of the extinguishing agent;
A hose, that is a flexible hose that allows easy addressing of the extinguishing agent in the appropriate directions (this may be lacking in small fire extinguishers, up to 3 kg);
An extinguishing agent that, sprayed or spread or placed in contact with the fire, interacts with this by switching it off or limiting it;
A propellant, gas suitable for the expulsion of the extinguishing agent.

Figure 1 shows the most common type of fire extinguisher, a permanent pressure portable. Of course different manufacturers will use different shapes, but the basic components remain the same.
In this model, there is a single tank, which the extinguishing agent is placed in a propellant gas atmosphere. The valve, to which tho hose is connected, is screwed or otherwise fixed non-permanently to the tank; on there is a label. The tank is normally made of metallic material (steel or aluminum in most cases), obtained by calendering, drawing and welding or by extrusion, and rests on a base 1b that can be integral to the tank or, as in figure, applied externally, but it is still necessary to allow the stable support on the ground; the ring nut 1a, usually internally threaded, allows connection to the valve. The valve is a principle composed of a body, normally made of molded brass, molten aluminium or high strength technical resins; an actuation pushbottom, a handle, a pressure gauge (or other pressure indicator), a safety device to avoid unintentional drives and finally a float. Some features are common to all fire extinguishers, such as red, the presence of a lifting handle, the safe; others are specific to permanent pressure fire extinguishers, such as the pressure gauge.

MAIN EXTINGUISH AGENTS

 

Water, a typical cooling agent which, by steaming thanks to the heat produced by combustion, changes its physical state into steam, which has a certain suffocation effect; recently, water mist systems have been realized, substantially of the extremely thin droplet sprayers, such as to create an air suspension with a strong water vapor release, having a suffocating effect. Non-toxic, inexpensive and easily available, it can not be used, apart from the nebulized one, in the extinguishing of light hydrocarbon fires as these would float on the water, re-establishing contact with the combustion oxygen and also creating dangerous boilover phenomena. Obviously, it can not be used on electrical or electronic equipment or at temperatures below 0 degrees Celsius, except for the addition of anti-freezing additives.

Carbon dioxide, normally stored in pressure vessels in the liquid state, it is still used effectively on live electrical equipment and on fires of class B and C. The fire extinguisher, emitting liquid carbon dioxide (immediately transformed from contact with the atmosphere into "carbon snow" ), the abrupt lowering of temperature (-78 ° C) and the strong subtraction of oxygen and allow you to break down the flames quickly without leaving residues (the crystals of carbon snow sublimate after a short time). On the other hand, they have a reduced effectiveness outdoors, limited range and nothing can on fires of class A. They require a minimum attention during use avoiding to remain asphyxiated due to oxygen deficiency or, currently remote possibility, to burn by thermal shock. They are strongly contraindicated on class D fires because of risk of explosions or violent reactions and of equipment that is affected by thermal shock.

Water extinguisher, containing an aqueous solution of foaming products called AFFF, acronym of aqueous film forming foam, which combine the cooling power of the water with the foaming capacities of the foam. They are very similar to foam extinguishers, varying in the chemical composition and percentage of foaming and equipped with a "shower" lance, necessary to improve heat subtraction. They have the main use on the fires of hydrocarbons (class B), of textiles, paper and wood (class A), combining the cooling activity of the water with the insulation of the film.Due to the high water content (97%) they can cause damage and accidents during use on electrical equipment (even if the fire extinguishers, by means of particular precautions, can sometimes allow their use without danger to the operator, within certain voltage limits and minimum distance). Ineffective on class C fires, they are strongly contraindicated on those of class D for development of flammable or toxic gases. They have limited range but in total visibility and prolonged discharge time (a few tens of seconds).

Foaming, which are not widely used in fire extinguishers and much more in fixed installations and large mobile shut off devices, are watery solutions containing strong surfactants and other additives (in the extinguishers the foam is only AFFF type). Through a lance, the liquid expands mixing with the air (venturi effect), generating a light foam with low expansion able to float on the hydrocarbons and isolate them from contact with the air, combining the choking action with the cooling power of the 'water. They are used almost exclusively on hydrocarbon (class B) fires but they also have a fairly good effect on those of class A. Totally ineffective on class C, D, E fires; the latter due to risk of electrocution. As for water extinguishers, they have the same range and duration.

Chemical powder, are probably the most used extinguishing agent. They have particular characteristics, as they are chemically modified by heat action and release inert gases, giving an incombustible or even active residue. The most widespread type, due to its universality of use and high efficiency, is the so-called polyvalent powder (known as ABC powder - able to extinguish fires in all classes except D); composed mainly of ammonium phosphate in a percentage between 40% (standard powder) and 90% (high extinguishing capacity).Of limited use, urea (Monnex powders) and potassium bicarbonate (Purple-K powders), called BC powders with very high extinguishing capacity, are used in the petrochemical industry and in airports for their exceptional effectiveness on fuels of liquid fuels and gaseous combined with the speed of abatement; not effective on solid material. Of special use sodium chloride, effective on fires generated by class D metals (sodium, magnesium, aluminum), which suffocates melting and reconstituting an impermeable crust. Sodium bicarbonate is also an extinguishing agent, a basic product of BC powders with ordinary extinguishing capacity, now in disuse. Rapid blast chilling, long throw, good durability and versatility make these fire extinguishers the most widespread on the market. On the other hand there is limited visibility during the discharge, irritation of the airways due to the breathing of powders during use (if poorly trained in closed rooms) and being dirty (the microparticles of dust infiltrate everywhere forcing a meticulous cleaning to eliminate every part of it). Contraindicated on delicate equipment.

Halogenated hydrocarbons: were among the first extinguishing compounds used in fire extinguishers, Some models were put on the market already in the early twentieth century, filled with carbon tetrachloride, subsequently replaced by less toxic and more effective agents, they had a successful moment between 1970 and 1990, for their characteristics of great extinguishing efficiency and total absence of residues. They are substantially of halogenated paraffinic derivatives, composed of chains of carbon atoms linked to a halogen between F, Cl, Br. Commercially named Halon followed by numbers of 3 or 4 digits representing the number of atoms, in the order of carbon, fluorine , chlorine, bromine. Thus, the carbon tetrachloride CCl4 is called Halon 104; Halon 1301 is a trifluoromonobromomethane, Halon 1211 (trade name BCF), difluorochlorobromomethane, Halon 2402 (trade name Fluobrene), tetrafluorodibromoethane. Banned worldwide due to the strong antagonistic activity of stratospheric ozone layer formation following the Montreal and Copenhagen protocols, they have been replaced by the so-called HCFCs (hydrogenated chlorofluorocarbons), of little success because they are very expensive and have limited capacity extinguishing but not harmful to the high atmosphere, such as decabromodiphenylethane.

 

TRANSPORTABILITY

An important characteristic of fire extinguisher is the transportability. The stantard charges indicates more up have to be compatible with the usability of the fire extinguisher; it is evident that a high mass extinguisher used by a child or a person who is somehow incapacitated can not be conceived. EN3 laws establish with a limit mass of 20 kg for fire extinguishers, and these are therefore referred to as portable. To this end, the regulations oblige the fire extinguishers to be equipped with lifting handles for easy transport, and support bases for safe storage. In recent years they have been developed to encourage the use also by people with physical impairments, domestic extinguishers with reduced dimensions and low weight. The domestic extinguishers are small, designed and manufactured to be kept at home in easily accessible places. The domestic fire extinguisher is an object that, despite its great usefulness, is not yet widely distributed in the market (especially in Italy). Beyond the limit of 20 kg (which in practice limits the mass of the extinguishing charge to 12 kg for dust, water and derivatives, and to 5 kg for carbon dioxide due to the high pressure bottle), extinguishers are generally equipped with wheels capable of pushing or towing (generally by hand); the regulations in force and in preparation entail the obligation. Fire extinguishers of this type are defined wheeled, and have total mass not exceeding 100-125 kg. Beyond this value, the devices of motorized towing systems are generally provided, realizing in practice small trailers, often approved for road use.

 

METHOD OF USE

The current laws defined fire extinguisher as a manual operated device. In the common use and according to the definition and according to the definition given above, other models can also be considered extinguishers. We can therefore define:

manual fire extinguisher: those that request the drive device placed on the fire extinguisher itself or on parts connected to it permanently;

automatic fire extinguisher those that are driven by the occurrence of particular causes (typically the temperature increase).

fire extinguishers with remote operation, generally used in areas that are difficult to access, they can be controlled by means of tie-rods and return systems (which limit their possible operating distance), or by means of pyrotechnic fillers which, usually, cause the blinding of blind discs with consequent expulsion of the extinguishing agent. Automatic fire extinguishers intervene autonomously when certain conditions occur. Almost all of these have closing systems equipped with temperature-sensitive equipment; in the most common cases, glass ampoules filled with mixtures of alcohols that change physical state at precisely defined temperatures, thereby causing the tube to explode, or bars made of two different coupled metals whose different expansion causes them to change at a defined temperature shot (bimetalli); in both cases a shutter is released, the fall of which allows the expulsion of the extinguishing agent through an orifice. It is possible to combine the two characteristics, obtaining automatic fire extinguishers with the possibility of remote actuation. In this case, the typical solution is represented by a valve with thermolabile phial and control for its breakage by mechanical action, by means of a firing device operated by the pyrotechnic cartridge and / or by a pull-rod system. Remote and / or automatic models are used in areas that are difficult to access or unmanned; for example the thermal power stations and engine compartments of ships. Some models are designed for the protection of electrical panels, cabinets containing flammable substances and engine compartments for cars and heavy vehicles. For example, they are mandatory on Formula 1 cars.

CLASSIFICATIONS

Fire extinguish can be classified according to:

Extinguish agent type:

Extinguish agent charge

Propulsion system

Transpirability

Method of use

 

CLASSIFICATION FOR EXTINGUISH AGENT

There are essentially three types of extinguishing agents, operating respectively by suffocation, cooling, chemical reaction; actions can be (and are generally) combined. Choking agents are those that prevent the contact between the combustible material and the comburent, such as inert gases (above all carbon dioxide and nitrogen), the molten salts that usually melt at the flame temperatures, and create a fluid layer, then cooled, which covers the fuel: typical case, sodium chloride, used to extinguish metal fires. Foamers are also examples, products that, in various ways, create a light enough foam to form an insulating layer between the fuel (for example a flammable liquid) and the comburent (the air) and compact enough not to allow breakage of the layer. Cooling agents are those substances designed to subtract heat from the fuel, to make it fall below the ignition temperature (above all water, but also carbon dioxide snow). Chemical reactive agents are those that react directly with the fuel, blocking chain reactions that occur during combustion (negative catalysis). Typical examples are chemical powders (minimally) and halogenated hydrocarbons, also called halons, but now banned due to their high level of harmfulness due to the stratospheric ozone layer. For the latter there are substitutes with low environmental impact, but these are very expensive extinguishers with limited efficiency.
Twin Agent wheeled fire extinguisher are used in places where there is a high risk of fire, where a fast and powerful fire suppression is required in a short time. This type of extinguishers consists of a trolley that supports three cylinders, two extinguishers of the same capacity (one of foam and one of powder) and the other of nitrogen, smaller, to pressurize the cylinders only at the time of use. The whole thing ends with a double tube attached to a special combined lance. The fire extinguishers can be divided into two types, already pressurized (referred to as «permanent pressure») or in the version to be pressurized at the moment of use by means of a propellant cylinder ("auxiliary pressure" fire extinguishers). This classification does not apply to extinguishers with own pressure, such as carbon dioxide, where the same extinguisher is also present in the gaseous phase. In portable fire extinguishers the bomb is loaded with carbon dioxide and can be internal or external to the tank, while the auxiliary pressure trolley trucks are equipped with a small external nitrogen bottle. In addition to the extinguishers proper, ie portable and wheeled, there are extinguishing units with higher charges, but these are generally self-propelled or towed vehicles, therefore not classifiable as fire extinguishers. The extinguishing units can be integrated into fire-fighting vehicles.

CLASSIFICATION FOR THE USE OF FIRE EXTINGUISHER

As we have seen, the fire extinguisher can contain different extinguishing agents, and these can be effective on different types of fires. As a consequence, there is a classification, officially sanctioned by the current regulations, tending to select fire extinguishers for employment.

Fire type
For this purpose, the European Standards Committee (CEN) defined the types of fire, according to the type of fuel. So there are:

 

Fire class A: generate by a solid combustibles like wood, paper, rubber and derivates, textiles, including metals.

Fire class B: generate by liquid combustibles like hydrocarbons, alcohol, solvents, fat mineral oil, ether, benzene and similr, solid liquefiable;

Fire class C: generated from gaseous fuels, such as hydrogen, methane, butane, acetylene, propylene;

Fire class D: generate by combustible metals potassium, sodium and their alloys, magnesium, zinc, zirconium, titanium and aluminum powder. They burn on the metal surface at a very high temperature, often with bright flame. From a regulatory point of view, there is no standard outbreak on which to perform tests for recognition of class D, but the manufacturer of the appliance must declare, under his own responsibility, the suitability of the fire extinguisher for this class of fire. The ISO standards provide for a more detailed classification, which distinguishes between liquid and solid metals, for example.

Fire class F: (class introduced with the EN.2 standard of 2005) generated by oils and greases in cooking appliances;

 

It is then defined a fire class E (not foreseen by the classification CEN), indicating the usability of the extinguisher on live electrical equipment, such as transformers, alternators, switches, electrical panels. The types of fire appear on the extinguisher depicted by means of pictograms, which are illustrated in the paragraph relative to the EN3 standards. Class E is not indicated by a pictogram, but by means of the inscription "USED ON ELECTRICAL APPLIANCES ON TENSION".

EN3 law also recognizes in Italy the class F, currently associated with water-based extinguishers with special additives with a film-forming action; these extinguishers are often equipped with a long spear to intervene with greater security. The EN3 standard does not require, for carbon dioxide extinguishers, the shutdown test for class C and the grey coloring of the upper part of the cylinders for portable fire extinguishers. These characteristics were instead required with the previous legislation (D.M. 20/12/82).

 

FIRE CLASS

The class of fire is a nominal volume or size of fuel, of a certain type (see above) that the fire extinguisher is able to extinguish. The classes are defined

as a volume of liquid in standard size tanks, for liquid fuel fires,

as the length in decimeters of a pile of squares of wood of a defined size, for fires of solid fuels;

The dimensions described above are standardized, and follow the Fibonacci sequence: 1 2 3 5 8 13 21 (27) 34 (43) 55 (70) 89 (113) 144 (183) 233, where the values 1 2 and 3 they are not used, and the values 5 and 43 are used only for type A fires. The values 27, 43, 70, 113 and 183, which are not elements from the Fibonacci sequence, have been maintained by tradition. There will then be fire extinguishers, for example of class 21A 144B, designation showing how the fire extinguisher, if used with expertise and in standard conditions, is able to extinguish a fire of a 2100 mm long wooden stack, and a circular tank containing 144 liters of liquid (lower water, upper n-heptane). Classes for type C fires are not defined: the standards only require the ability to interrupt the flame generated by a standard LPG burner, without distinguishing dimensions or other quantities. The fire extinguisher mentioned above, if capable of extinguishing the standard gas fire, will have designation 21A 144 B C. Type D fires are not defined by the standards, whereas for type E a dielectric test is only defined to demonstrate the capacity not to conduct electricity from an electrical source to the extinguisher operator. For example, a good multipurpose powder fire extinguisher of 6 kg of extinguishing mass will have class 34A 233B; a good 5 kg class 113B carbon dioxide fire extinguisher; the fire extinguisher for the car, if it only extinguishes the fires of gasoline, 55B or, if it is able to extinguish also flames coming from the upholstery or saddlery, 8A 55B.
In the case of fire extinguish of big dimensions of wheeled type, while maintaining the same definition for the types of fire, the classes are defined differently. In view of the large capacities, it is considered for type A fires only the ability to extinguish a firewood of certain dimensions within a maximum time, and for the fires of liquids the extinction time of a 233 liter tank. We will then have designations of type A-B1, which shows that the fire extinguisher is able to turn off both the wooden stack and the tank, and this in a short time, B2 means a longer time, and so on; obviously a fire extinguisher B1 is preferable to a B2.

PROPELLANT TYPE CLASSIFICATION

Almost all extinguishers expel the extinguishing agent by using propellant gases. In fact, appliances such as pump-type water sprinklers are not considered as extinguishers, also used in switching off the wood fires (some of them, in fact, pump air that expels the water, and therefore fall in the previous case).Some extinguishing agents are self-propelled, and the typical (and practically the only) case is carbon dioxide, which is stored in high pressure cylinders in the liquid state (provided that it remains below the critical temperature). Since atmospheric pressure and ordinary temperatures the carbon dioxide is in the gaseous state, the same -which is also the extinguishing agent - comes out of the extinguisher by simple pressure difference. All other extinguishing agents, on the other hand, require a propellant gas. Although air is often usedsed, which contains the oxygen comburent, as a propellant (practice permitted by the standards), the best propellants are obviously inert gases, and among these are used nitrogen and, again, carbon dioxide; very rarely helium and argon; helium is sometimes used using the simplicity of its tracking by spectroscopy in order to detect leaks during construction or maintenance. In general, nitrogen or air is used in permanent contact with the extinguishing agent (permanent or pressurized extinguishers), while carbon dioxide is often stored in closed cans and put in contact with the extinguishing agent only immediately before use (internal / external bomb fire extinguishers). Each of the two systems has its own advantages and disadvantages: in general, the bomb extinguishers make it possible to have no containers subjected to pressure in positions likely to receive shocks (there is for example a potential risk for fire extinguishers mounted on mobile means, such as trucks and the like, although the regulations require particular checks to avoid the danger).On the other hand, the permanent pressure fire extinguisher is of simpler (and therefore safer) and less expensive construction. In the past, pressurized liquefied gases have been used as propellants, in particular freon 11 and freon 12 - often in mixture - which had the advantage of being practically inert or even weakly extinguishing, conserved at low pressure and therefore usable with commercial tanks of great diffusion (and low cost) like spray cans. In the 1970s there was large production of fire extinguishers of this type, with powder extinguishing agent or, later, Halon. The banishment of freon (and Halon), inhibitors of ozone formation, and the introduction of rules that have regulated the market, once wild, of the extinguishers, have effectively decreed the end. Finally, there is the theoretical possibility of operating the fire extinguisher with propellant gas generated by pyrotechnic explosive charges, on the model of pressurization of the airbags but they are still in the experimental state.

CURRENT LAWS

Fire extinguisher are generally subject to approval of offcial bodies that verify the correspondence to precise reference standards. For portable fire extinguishers, the EN 3 standards, which are repeatedly updated, apply in Europe. Basically, the EN 3 rules establish that the fire extinguisher must have some fundamental characteristics:

Type identifiability, extinguishing agent, use, effectiveness, for which they require the presence of an explanatory label that shows the pictograms identifying the types of fire on which the fire extinguisher can be used (see figure), the type of extinguishing agent and the classes obtainable, in addition to the already mentioned red color (RAL3000).(pictograms awaiting authorization by CEN)

Simplicity and adaptability of use, for which the fire extinguisher must have obvious methods of operation, do not require repeated actions and, beyond a certain mass, be equipped with a hose that allows the easy tilting

Safety of operation, so that all the parts subjected to pressure must comply with particular requirements.

Effectiveness, whereby a given mass extinguisher must meet minimum fire classes.
Substantially equivalent to EN 3 standards are ISO 7165, of US origin, which however impose different characteristics and tests. Wheeled fire extinguishers are less defined than laptops, obviously being of more specialized use. There are no general rules for towing fire extinguishers, without prejudice to aspects relating to the safety of pressure vessels and, where appropriate, to compliance with transport regulations.

In Italy the last decree on the matter is the DECREE 7 January 2005 - Technical and procedural standards for the classification and approval of portable fire extinguishers, published in the Official Gazette of the Italian Republic no. 28 of 4 February 2005; through which the transposition of the EN 3-7 Standard occurred. The maintenance of fire extinguishers is regulated by the national standard UNI 9994, which specifies the modalities and the minimum frequency of the various maintenance operations. Synthetically, it is possible to summarize the various maintenance phases:

Surveillance: preventive measure aimed at verifying the presence, integrity and accessibility of the extinguisher. It is performed by trained personnel present on site; it is a simple visual examination and therefore does not replace the operations indicated below, which must be carried out by qualified and equipped personnel. Surveillance is carried out on a monthly basis.

Control: operation every six months, to verify the proper functioning of the appliance. The control consists in an external visual examination of the extinguisher, and in the verification of the pressure of the propellant gas through certified external pressure gauge (permanent pressure extinguishers). Carbon dioxide fire extinguishers, and propellant bombs (for auxiliary pressure fire extinguishers), are checked by weight measurement, since for various reasons it is preferred not to refer to the pressure.

Revision: operation to verify the efficiency and the state of conservation of the extinguisher and of all its components, includes the replacement of the extinguisher and of the safety devices against overpressure. The revision requires the disassembly of the valve unit and the internal inspection of the tank, in this phase it is preferable to replace the gaskets. The frequency of the operation depends on the type of extinguishing agent (foam or water: 24 months, dust: 36 months, CO2: 60 months, halogenated hydrocarbons: 72 months).

Testing: verify of the tank stability refers to pressure. Operation frequency depend on the extinguisher type and from the date of construction: CO2 extinguishers are subject to ISPESL directives for compressed gas cylinders (ten-year testing with tank punching), all others must be tested every 12 years if the tank is CE marked, or every 6 years if constructed before the obligation of CE marking (PED directive). In the latter case the test is carried out at a pressure of 3.5 MPa, in the previous cases reference is made to the test pressure shown on the tank or bottle.

RECOGNITION
 

On fire extinguishers manufactured in Italy there are no symbols of recognition or written to determine from the distance the type of extinguishing content (marking present instead in other countries such as the United States and England). In principle, we can remotely recognize the extinguishers from their hose or dispenser, shown as examples below.