It is known how, owing to the continuous increase in atmospheric pollution and the particular environmental conditions of some specific manufacturing activities, the persons at risk are forced to breath through special filtering devices such as, for example, those contained in special masks.

It is also known that said masks are difficult to use because of their size and the awkward nature of the fastening devices for fixing them to the face, resulting in their being practically unusable for example in the case of cyclists and/or motorcyclists who also have to wear a protective helmet.

The technical problem is therefore that of providing an air filter device which has a low weight and small size and is practical and simple to fit during use and remove after use.

Within the scope of this problem a further requirement is that the filter device should be provided with means for keeping it fixed to the face, which can be easily replaced in the event of breakage or the like.

These technical problems are solved according to the present invention by an air filter device comprising means in the form of a mouthpiece allowing the user to grip and retain the device itself.

Further details may be obtained from the following description of a non-limiting example of embodiment of the invention provided with reference to the accompanying drawings in which :

- Figure 1 shows a first example of a filter device according to the invention fitted to a mask of the anti- gas type ; - Figure 2a shows a plan view of the means for gripping and retaining the mask according to Fig. 1 ; - Figure 2b shows a side view of the gripping and retaining means according to Fig. 2a ; - Figure 3 shows a second example of embodiment of a filter device according to the invention ; - Figure 4a shows a plan view of the gripping means of the device according to Fig. 3 ; - Figure 4b shows a front view of the gripping and retaining means according to Fig. 4a ; - Figure 5a shows a further example of embodiment of the filter device according to the invention ; - Figure 5b shows fitting of the device according to Fig. 5a underneath a full helmet ; - Figure 6a shows an example of embodiment of the filter device with the arrangement, in between, of a heat and moisture exchanger ; and - Figure 6b shows a cross-section along the plane indicated by VIb-VIb in Fig. 6a.

As shown in Fig. 1, a first example of embodiment of the air filter device according to the invention comprises an anti-gas mask 10 which is of a size and made of material such as to cover the nose and the mouth and adhere to the skin so as to prevent infiltration.

A filter element 20 of the conventional type and therefore not described in detail is arranged in the bottom part of the mask 10.

The mask 10 is associated with retaining means consisting of a mouthpiece 30 provided with a pair of extensions 31 allowing it to be gripped and retained by the user's teeth.

On the opposite side to the extensions 31, the mouthpiece is extended by a substantially cylindrical section 32, the free part of which terminates in a plurality of protrusions 32a arranged in succession adjacent to one another.

Said cylindrical extension basically forms a device for adjusting the length of the mouthpiece 30 since, by introducing the end provided with protrusions into a corresponding hole in the mask, it is possible to achieve the correct adjustment in relation to individual needs ; any surplus protrusions projecting outside the mask itself (Fig. 1) may be cut along any specially provided pre-weakened breakage lines.

In the case of use together with a mask, the gripping and retaining element 30 associated with the mask itself may be solid in that respiration is performed through the nose.

As illustrated in Fig. 3 the filter device 110 may also be provided without an anti-gas mask : in this case the mouthpiece 130 is directly inserted into the filter means 120 which will be provided with a special through- hole for insertion of the cylindrical section 32 with protrusions 32a for allowing adjustment of its length.

In this case where no mask is used, the gripping element 130 is substantially hollow so as to allow respiration via the mouth.

Both in the version with mask and in the version without mask, it is envisaged that the filter device 310 may be associated with a heat and moisture exchanger which is known per se and therefore only schematically indicated by 40 in Figs. 6a, 6b in which 41 also indicates the characteristic surface of the external casing similar to that of a blind.

Said exchanger 40 retains the vapour and the heat during expiration and releases said vapour and heat during

inspiration, thus preventing drying of the air ducts and the formation of condensation.

In the version without mask, the filter device is particularly suitable for use together with motorcyclists'helmets and may also be constructed as the version 210 shown in Fig. 5a in which the substantially cylindrical section 232 of the mouthpiece 230 forms a suitable angle with the mouthpiece itself.

In this way the device may be easily inserted underneath a full helmet as shown in Fig. 5b ; the presence of the exchanger 40, in this case also, prevents the formation of condensation inside the helmet.