People protect themselves against poison in the air by using a gas-mask. It is well-known that, despite the use of masks, accidents still regularly occur, leading sometimes to extensive health damage for the bearer of the mask, mostly firemen, laborers in the chemical industry, disaster prevention teams and similar services. The cause of these accidents is very often that the bearers feel overly safe and therefore fail to recognize leaks at the point where the mask closes around the face or technical defects of the mask itself. It is also difficult for the bearer to define the danger involved in a fire accident when for instance carbon-monoxide is emitted.

Carbon-monoxide is a poisonous gas that can not be held back by normal filters and therefore is able to penetrate through to the bearer of the mask.

This invention aims at increasing the security of the bearer of a gas-mask.

According to the invention, at least one sensor is placed inside the mask to react sensitively toward harmful gas or vapors leaking into the mask and to provide corresponding warning signals.

Such sensor may be elected among the known gas sensors, for instance gas sensors energized by a power source and adapted to provide an electric or electronic signal when exposed to a specific gas.

Preferably, sensors are to be used which comprise a gas-sensitive active film made of metal-oxide. A ceramic plate as well as a heated silicium membrane can be used as support of the film.

Preferably, the warning signals are used to control appropriate warning systems in or on the mask to inform the bearer of the mask, for instance either visually or acoustically, about harmful leak.

This could take place in form of LED's placed within sight range inside the mask.

According to the invention, the sensor should be set in a technically optimal place.

Preferably, means are provided to eliminate the influences on the sensor of moisture in the air.

Sporadic breathing out into the mask raises the air-moisture drastically, whereas breathing in considerably reduces the air-moisture drastically. This intermittent fluctuation of the air-moisture may affect the traditionally operated gas sensors. For this reason an evaluation strategy may be used to prevent these disadvantages. Evaluation strategies as described for instance in details in the German patent applications P196 17 297.7 and P195 43 296.7.

A cheaper embodiment may comprise only one sensor, i. e. for applications in which high-toxics are to be expected, whereas more elaborate embodiments may comprise two or more sensors.

In the case of cheaper embodiments the sensor is placed in a sensor-technically optimal spot, preferably close to the mouth and to the nose of the bearer.

In other embodiments, a sensor is placed between a filter element and a backlash valve located in the air inlet of the mask, to monitor the filter. Such sensor is not irritated by the breathed out air-moisture However, a disadvantage is that leaks, for instance between the mask and the head, remain undiscovered. According to the invention, to be able to recognize the danger resulting from this, a further sensor is placed inside the mask,

preferably in the direct vicinity of the nose and mouth of the bearer, so as not to be subjected to extreme moisture fluctuation.

According to the invention, the sensor element is advantageously separated from the breathing space of the mask by means of a membrane.

In this case a semi-permeable membrane is used, i. e made of stretched PTFE-film. Gas has a tendency to maintain the same gas-pressure. For this reason gas molecules diffund without noticeable prolongation of the reaction time through such films, whereas saliva droplets, condensation water and similar are shut out. These films are preferably placed either single or multi-layered in the form of a sandwich between wire mesh, causing the film and the sensor-element to be protected against larger air-movements and mechanical damages.

Usually, the sensor or the sensors are energized from a power source, for instance batteries having sufficient capacity for a normal period of use, very often a couple of hours. When the batteries cannot be placed within the mask, the invention suggests that an electric cable or plug (i. e. induction) should be led gas-tightly from the mask to a battery case which can be worn either on a belt or shoulder strap. This ensures simple exchanging of the battery even during operation The invention can be designed in numerous variations The common objective is, however, that gas sensors are placed inside the gas mask which are evaluated by appropriate electronics, whereby the bearer of the mask is appropriately warned against gases leaking into the mask.

The drawing schematically shows an embodiment of the present invention, given as an example only.

In this example, the mask is constructed as a form-adaptive cover (1) of the facial area, usually made

of rubber or formable synthetic indian rubber, and maintained on the head by appropriate strips (2) or similar in order to provide a closed breathing space (3) in front of the mouth and of the nose of the bearer. The air flows into the breathing room through an inlet (4) provided with an adaptable filter (5). A valve (6) ensures that the air breathed out leaves the mask through special exits (7) rather than blowing out through the filter-element. Valves (8) are also placed within these exits to stop the inflow of unfiltered air.

The filters used for gas-masks are mostly multi-layered. They hold particles back mechanically.

Chemical impregnations combine several gases and vapors.

According to the invention, the mask is provided with a first sensor (9) located close to the mouth and to the nose in the space (3) determined within the mask in front of the mouth and of the nose, and with a second sensor (10) located between the filter (5) and the valve (6). Bot sensors are connected through a plug (11) to a power source (12) and are connected to a visual display (13) located on the window of the mask. For the clarity of the drawing the connection between the plug and the power source and the connections between the sensors and the visual display have not been shown.

The invention is not limited to this embodiment.