Large scales

The large scales , also called air scale or car scale , is a vehicle used by the firemen, and which carries a retractable scale great height. The term “large scales” is used by the general public, the professionals speak quite simply “about scale”, or use an abbreviation (in France: EPA, EPSA).

The large scales allow:

to carry out rescues in the stages when the normal accesses are difficult: evacuation of the people;
to convey personnel and materials;
to sprinkle by outside.

Certain scales have telescopic rigid pipes which make it possible to convey water in top, with the image of a Colonne dries. The top of the scale is in general connected to bottom by an intercom.

The first models were actuated with the hand, by cranks. The modern models are actuated by engines. In many cases, the scale is provided with a nacelle which assembles and descends, into fixed or removable, and thus ensures a great safety.

The last years saw appearing lifting arms within the bodies of firemen. These machines, although not being scales, have a similar function. There are two types: with two hinged jibs or a telescopic arm, but all are provided with a large platform being able to receive up to 300 kg of load. Their paramount advantage is to be able to overhang the building or the zone of the disaster, and to provide an important platform of work in height. Their principal disadvantage is an implementation slower than the scales, preventing them from being employed like machines of rescue.

Safety of intervention

The first risk is the imbalance of the vehicle: indeed, the scale constitutes an arm of lever which amplifies the forces (see the article Moment of a force). Consequently:

the vehicle, once places from there, “is raised” by hydraulic actuating cylinders in order to not rest more on the wheels (the wheels touch the ground but do not support any weight): indeed the movement of the suspensions of the vehicle would endanger its stability;
the slope of the scale is limited by the deployed height.

The second risk is the fall of the people. The firemen must thus be provided with a go along being able to absorb the shock of the fall. But this device can be set up only with one nacelle, or when the fireman arrived in top.

In France

In France, one distinguishes mainly three types of scales:

the scales on carrier (ESP) : they are scales on carriage, the carriage being assembled on a vehicle; these scales are of an old model, but make it possible to intervene in narrow streets;
the swivelling scales semi-automatic (EPSA) : the scale is posed into fixed on the vehicle; it can make one movement at the same time: deployment, rise or swivelling;
the swivelling scales automatic (EPA) : similar to the EPSA, they can carry out several movements simultaneously.
the articulated lifting masts (MEA) , also known under the name of articulated lifting arms (BEA or CBEA) , they are a complement on air scales.

The initials are also found:

EPAA : articulated swivelling scale automatic: the last side can incline
EPAC : scale swivelling with combined actions (equivalent of EPA)
EPAN : swivelling scale automatic with nacelle
EPAS : automatic swivelling scale sequential (equivalent of EPSA)

According to the legislation, the establishments receiving from the public (ERP) a certain height must be served by ways (streets) sufficiently broad to give access to a swivelling scale; these ways are known as “ways scale”.

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