The UNI EN 3/7:2004 standard is about characteristics and performance requirements of portable fire extinguishers and their test methods. It is a standard, then, that establishes not only the general characteristics of portable fire extinguishers, but defines also the different fire tests fore every fire class. The only class that is left out is class D, because fires generated by metals differ too much from each other to be represented by an only one fire test, and the suitability of fire extinguishers has to be ascertained on a case-by-case basis.
CHARACTERISTICS OF FIRE EXTINGUISHERS
The first point that this standard considers is the characteristics of a portable fire extingusher. Here, fire extinguishers are classified according to their extinguishing agent (water based, powder, CO2, halons and clean agent).
It is here established that the portable fire extinguisher is made of a body, a control valve, of some device allowing fot the extinguishing agent to flow out (hose, horn or nozzle), a closure assembly, an operating device and the extinguishing agent.
The control valve is essential to temporarily interrupt the extinguishing agent erogation. The hose is necessarily present on every fire extinguisher whose extinguishing agent exceeds 3 Kg (or 3 L), and it must be 40 cm long or more. If the hose is on a smaller fire extinguisher, it can be shorter (until 25 cm).
The fire extinguisher must be designed so to be as easy to use as possible, therefore the control and operating devices shall be on the top of it. The fire extinguisher has to be ready for use, without the need of disassembling or assembling before use, and the strenght needed for the operation cannot be excessive. On the other hand, there is the necessity of a safety device to avoid an accidental activation. Such safety device has in turn some other safety device, to understand if it has been broken.
All fire extinguishers, including water based ones, shall be rustproof. Fire extinguishers need to be tested also to verify this feature. To verify their resistance to external corrosion, samples (two with the same size or two from the same group but with different sizes) are tested in saline fog for 480 hours, and then they are carefully cleaned. To test the resistance to water based extinguishing agents, samples are tested with 8 temperature cycles. When these cycles end, both extinguishing agent and fire extinguisher are examined.
The only allowed propellant are: air, argon, carbon dioxide, helium and nitrogen (with the exception of stored-pressure water-based fire extinguishers).
Last, it is decided that every stored pressure fire extinguisher, with the exception of carbon dioxide ones, shall have a device to check their pressure.
TESTS ON FIRE EXTINGUISHERS
In this text, the rules for fire tests are established; we have already discussed this topic in another post. Before every test, fire extinguishers are to be maintained at a 20 °C temperature for at least 24 hours. Both water based and dry chemical/powder fire extinguishers need to go through the compaction procedure.
This standard also states the permitted rated loads for every fire extinguisher category (1, 2, 3, 4, 6, 9, 12 for dry chemical/powder fire extinguishers, 2, 3, 6, 9 for foam/water based fire extinguishers, 2, 5 for carbon dioxide fire extinguishers, 1, 2, 4, 6 for halons) and the width of the reloading hole (20 mm for 3 Kg rated load fire extinguishers or less, 25 mm for bigger ones).
PROPELLANT
The standard goes on regulating the control of the pressure of the propellant. In this case, there is need of a lid to hold the pressure and some device for directly checking it (a pressure gauge or a pressure indicator).
Fire extinguishers and propellant cartridges shall be tested to verify that the leaks are not excessive.
DIELECTRIC TEST
The suitability of fire extinguishers for their use on live electrical equipment needs also to be certified, besides their belonging to fire classes. Water based fire extinguishers should pass a dielecetric test, that is a test that verifies the ability of a fire extinguisher to pit out a fire on a live electrival apparatus without damaging it. During the dielectric test, the electrical conductivity of the flow is measured, and this must stay under the given limits.
These is the permitted apparatus for the test:
1. A metallic plate vertically hung to insulators, at least 1 m far from any object or structure.
2. A trough or other container, put under the plate to collect the liquid that is going to drip from it and that needs to be isolated from the floor.
3. A high voltage transformer that permits to generate an alternating voltage of 35 kV between the plate and the soil.
4. An insulating support for fire extinguishers with a fixed nozzle or an insulating tray for fire extinguishers with a hose.
The voltage will be measured through an ammeter connected between fire extinguisher handle and earth and between nozzle and earth. The fire extinguisher is activated and we can measure the voltage.
PRESSURE GAUGE AND PRESSURE INDICATOR
There are also tests for pressure gauges, to be sure they correctly evaluate the pressure in the tank. All tests are performed at 20 °C. On the pressure gauge there should be a zero sector, a green sector and two red sectors at both sides of the green one. The needle on the pressure gauge should always be clearly visible, no matter which sector it is pointing. Obviously, all the parts of the pressure gauge that could comein contact with the extinguishing agent wukk be compatible with it or protected from it.
The pressure indicator shall point out if the fire extinguisher is able to operate, and the variation on the indication between operative and non-operative will coincide with the minimum operating temperature pressure.
After the discharge of the extinguishing agent, any pressure indicator will point out the lack of pressure.
HORNS
A whole section is about horns for carbon dioxide fire extinguishers. Carbon dioxide, indeed, comes out at such a low temperature that it may cause frostbites when coming in contact with the user. If the user is forced to hold the actual horn (in case this is coupled to a hose), there should be a handle to protect the hands from touching carbon dioxide. Furthermore, the couplings between the horn and the other parts of the fire extinguisher need to be checked to verify it will not detache or loosen.
STANDS
Fire extinguishers often come with a stand. In that case, the stand should be compliant with specific requirements as well. Getting into the details, it has to be easy for the user to take the fire extinguisher from the stand, that should be capable of sustaining twice the weight of the fire extinguisher.
FIRE RATING
Tests are performed on fire extinguishers to establish their fire ratings. These tests as well are defined in this standard. A fire extinguisher passes a test when it can put out two test fires out of three. Each three-test series should be completed before a new one can start, and here is no limit to the amount of series that can be performed on the same type of fire extinguisher, but all the fire tests in a series should be in sequence. The test operator will wear appropriate equipment (helmet, gloves and visor are permitted, an aluminium suit is not).
We have already discussed about class-A and -B fire tests in another post on this site, and they are exactly the ones described by UNI EN 3/7:2004 standard.
MORE FEATURES OF PORTABLE FIRE EXTINGUISHERS
Part 16 of UNI EN 3/7:2004 is about identification of portable fire extinguishers, that is to say those visual features that let us immediately indentify that object as a fire extinguisher. The colour of fire extinguishers must be red RAL 3000 (as specified in Farbregister RAL-841-GL), although it is permitted that an area no larger than 10% of the whole surface is a different colour, in compliance with national regulations, to identify the extinguishing agent inside of it.
The label should be clearly visible, so its colour should contrast with the background.
MAINTENANCE
Specific rules for fire extinguisher maintenance are not set in this standard, it just recommends regular maintenance. Each nation shall issue national standards to regulate the maintenance.
COMPACTION PROCEDURE
The last annex of UNI EN 3/7:2004 is about the compaction procedure. Also the characteristics of the compaction machine are decided here; it will work only on a fire extinguisher at a time. The fire extinguisher is compacted when it is full and loaded with the extinguishing agent as specified by the manufacturer at 20 °C. The fire extinguisher is put in the compaction machine that make it fall vertically on a steel plate five hundred times from a 1.5 cm heigth.
