US3725011A - Automatic fire alarm with at least one measuring chamber - Google Patents

Abstract

AN AUTOMATIC FIRE ALARM POSSESSING AT LEAST ONE MEASURNG CHAMBER ACCESSIBLE TO THE SURROUNDING AIR AND CONSTRUCTED SUCH THAT IT CAN DELIVER BY MEANS OF AN ELECTRIC CIRCUIT AN ALARM SIGNAL WHEN COMBUSTION PRODUCTS, IN THE FORM OF COMBUSTION AEROSOLS OR SMOKE, PENETRATE THE MEASURING CHAMBER. ACCORDING TO THE INVENTION THE MEASURING CHAMBER CONTAINS A SOLID OR LIQUID SUBSTANCE WHICH, IN THE COURSE OF TIME, GIVES OFF A GASEOUS REACTION AGENT SUITABLE FOR FORMING WITH HYDROGEN HALIDE VAPORS CONDENSATION PRODUCTS IN THE FORM OF AEROSOLS.

Description

A ril 3, 1973 A. PURT ET AL 3,725,011

AUTOMATIC FIRE ALARM WT'IH AT LEAST ONE MEASURING CHAMBER Filed March 13, 1970 I 15 i5 5/ 13 u. 11 r j 9 I 11 3 Fig.2

21 26%19 U u //l\\ 1s [1 20 17 F 3 INVENTORS Gusrnv A- Pun-r WnLrR 6055mm BY MW a! M ATTORNEY United States Patent O 3,725,011 AUTOMATIC FIRE ALARM WITH AT LEAST ONE MEASURING CHAMBER Gustav A. Purt, Rapperswil, and Walter Bosshard, Stafa, Switzerland, assiguors to Cerberus AG, Mannedorf, Switzerland Filed Mar. 13, 1970, Ser. No. 19,244 Claims priority, application Switzerland, Mar. 28, 1969,

4 69 Int. Cl. G011! 21/26, 23/12; G08b 21/00 US. Cl. 23-254 E 16 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to an improved automatic fire alarm of the type possessing at least one measuring chamber freely accessible to the surrounding air and constructed such that it can deliver via an electric circuit an alarm signal when combustion products in the form of combustion aerosols or smoke penetrate into the measuring chamber.

Automatic fire alarms of the above-mentioned type possess a measuring chamber equipped with openings through which the surrounding atmosphere can enter such measuring chamber, for instance by convection. The products of combustion appearing during a fire, for instance smoke particles or combustion aerosols, can be detected in the measuring chamber in different ways.

A known optical fire alarm incorporates a light source which directs light upon a photocell. Smoke particles cause a variation of the illumination intensity and the photocell current, this current variation being used for sounding an alarm, for instance by means of a bridge circuit or a reference ray path without weakening the light.

In another known optical fire alarm use is made of the Tyndall efiect. The lamp and the photoelectric cell are arranged in such a way that no direct light impinges upon the photocell. When smoke is present in the measuring chamber the photocell receives stray or dispersed light and the photocell current is used for sounding an alarm.

Ionization fire alarms operate according to another principle in which the measuring chamber is equipped with two voltage-carrying electrodes and a source of radioactive radiation. A current of ionized gas molecules or atoms flows between the electrodes. If the gas composition changes or the content of larger particles, such as for instance aerosols or smoke, then the ionization current will also change. This change in current is employed for sounding an alarm through the agency of an amplifierand threshold value detector circuit.

Instead of relying upon convection for delivering the atmosphere containing the combustion products to the measuring chamber, such atmosphere can also be delivered thereto by suitable suction devices, for instance via pipe conduits.

The described prior art constructions are sufiicient in most instances for giving an early enough warning of the existence of a fire. However, a pre-condition for proper functioning is that the combustion products exist in the form of aerosols or smoke.

However, the increased use of plastic has resulted in the fact that with fires at low temperatures or with pyrolytic disintegration as the initial phase of a fire, oftentimes aerosols are only present in small quantity or not at all, but instead there exist in considerable quantity gaseous combustion products which can be only detected with great difficulty by means of the heretofore described prior art fire alarms.

Especially, with the use of halogen-containing plastics, for instance polyvinylchloride (PVC), gaseous hydrogen halides, for instance hydrogen chloride or hydrochloric acid vapors, occur during a fire which are very corrosive. Even small quantities can cause considerable damage.

However, such hydrogen halide vapors can only be detected by the described fire alarms With great difiicnlty. Thus, for instance, with ionization fire alarms the de tection sensitivity is small because of the only slightly larger molecular weight of the hydrogen chloride in comparison to that of air molecules. Only with a sufficiently large moisture content of the air are there formed hydrochloric acid droplets in large enough quantities. Only in this instance are ionization fire alarms sufficiently sensitive to be also used for hydrochloric acid vapors.

Techniques are known for ascertaining the presence of disturbing gases in an atmosphere in that the atmosphere is additionally decomposed by means of a reagent. This reagent forms with the gas to be detected a fine mist or fog. Hydrogen halides, for instance hydrogen chloride, can be determined in this manner independent of the moisture content of the air, by mixing with ammonia as the reagent.

Devices have become known in which the atmosphere to be examined is subjected to suction, ammonia being added to the gas stream, the ammonia is chemically produced or from an ammonia solution. The fog or mist resulting during mixing With a hydrogen halide-containing gas is observed or detected in the usual fashion. Such devices, for instance leak detectors, however, generally react specifically only to a certain substance to be determined and are therefore usable only as a warning device during the processing or detection of certain chemicals. Additionally, they require continuous operation of an air circulation installation and the continuous production and delivery of suitable gaseous reagents. Such must be present in excess quantity in order to aiiord good detection sensitivity, since during the circulation of air they are consumed in considerable quantity. Such devices are therefore hardly suitable for continuous operation.

On the other hand, an automatic fire alarm is required to work faultlessly free of wear over a long period of time, and additionally, that it respond to all possibly encountered products of combustion.

SUMMARY OF THE INVENTION Accordingly, it is a primary objective of the present invention to provide an improved automatic fire alarm which is not associated with the aforementioned drawbacks of the prior art constructions.

Another, more specific object of the present invention is the provision of an automatic fire alarm which responds both to combustion products in the form of combustion aerosols or smoke and to hydrogen halides and which can work effectively for long periods of time without maintenance.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the inventive automatic fire alarm is of the type incorporating a measuring chamber which contains a solid or liquid substance which, during the course of time, delivers a gaseous reaction agent suitable for forming, with hydrogen halide vapors, condensation products in the form of aerosols.

A particular characteristic of such substances is that their vapors, either because of the partial pressure in the temperature range of 25 C. to +100 C., or because of their chemical nature, do not appreciably influence the detection sensitivity of combustion aerosols.

In order to maintain the giving off of gas for as long a period of time as possible and in order to prevent any disturbing influence upon the surroundings, it is especial- 1y advantageous to select a substance which, at room temperature, possesses a reaction agent vapor-partial pressure below 100 torr.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood, and objects other than those set forth above, will become apparent, when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:

FIG. 1 is a sectional schematic view of a fire alarm utilizing light absorption for its operation;

FIG. 2 schematically illustrates in sectional view a fire alarm utilizing dispersed or stray light for its operation; and

FIG. 3 schematically illustrates in sectional view an ionization fire alarm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, the optical fire alarm shown in FIG. 1 comprises a measuring chamber 1 having at its wall 2 openings 3 allowing the entry of external air to the interior of this measuring chamber 1. The incidence of direct light is prevented through the use of the diaphragms or light stops 4. A lamp 5 and a photocell 6 are located in the measuring chamber 1. Lamps 5 and photocell 6 are arranged such that direct light from the lamp 5 impinges upon the photocell 6. Now if smoke enters into the measuring chamber 1, then a portion of the light is absorbed by the smoke and the illumination intensity at the photocell and, thus, the photocell current changes. This photocell current is evaluated via the leads or conductors 7 by means of a non-illustrated electric circuit suitable for this purpose, and well known to the art, and, if desired, that is to say, when the light absorption in the measuring chamber 1 has reached a certain degree, can be employed for sounding an alarm.

Apart from the foregoing, it is to be understood that the invention contemplates providing a substance 8 in the measuring chamber 1 which has the properties of slow- 1y delivering reaction agent vapors during the course of time. If the air entering through the opening 3 by natural convection only has traces of a hydrogen halide, for instance gaseous hydrochloric acid, then upon wiping contact with the substance 8 there is formed a fine-suspended particle mist which will be detected by the fire alarm in the same manner as smoke.

The described fine alarm thus responds equally sensitively to smoke as such occurs normally during a fire as well as to hydrochloric acid vapors resulting from combustion of PVC.

Naturally, all known constructions of optical fire alarms which work with light absorption, can be provided with such additional ammonia-delivering substances. Likewise, all known photoelectric elements, such as photocells, photo resistors, solar cells and so forth, can be used. Similarly all known circuitry for alarm installations can be used as the electric circuit.

FIG. 2 illustrates an optical fire alarm utilizing the Tyndall effect for its operation. Once again, the wall 9 of the measuring chamber 10 has openings 11 for the entry of air. These openings are covered by parts of the wall in such a way that it is impossible for light to directly enter from the outside. In this instance, the lamp 12 and photocell 13 are arranged such that no direct light impinges from the lamp 12 upon the photocell 13. This photocell 13 is thus without current in its rest condition. If smoke enters the measuring chamber 10, then, a portion of the light transmitted by the lamp 12 is dispersed to the photocell 13, and a photocell current can be observed at the conductors 14 which can be used by an elec tric circuit to sound an alarm. Here again, in a corner of the measuring chamber 10 there is placed a reaction agentdelivering substance 15 which communicates with the interior of the measuring chamber 10 by openings in the wall. Accordingly, a certain partial pressure of reaction agent prevails in the measuring chamber 10. If the air entering the measuring chamber 10 contains traces of hydrogen halide, then, once again, there is formed a suspended-substance mist which, in the same manner as smoke causes light to disperse, therefore results in the presence of a photocell current as previously explained. Also, in this instance, the construction of a fire alarm and the application of the reaction agent-delivering substance in the measuring chamber can be optionally selected and according to the desired purposes.

FIG. 3 depicts an ionization fire alarm wherein its measuring chamber 16 is surrounded by an external or outer electrode 17 having a number of small openings 18 rendering possible the entry of external air. Internally of the measuring chamber 16 there is located a punch-shaped inner electrode 19 which carries a suitable radioactive preparation 20. A partition wall 21 separates the measuring chamber 16 from a second ionization chamber 22 serving as a reference chamber and connected in series with the measuring chamber 16. By means of a hood member 23, serving as an outer electrode, this reference chamber 22 is almost sealed from the external air so that smoke particles cannot penetrate into such chamber, but a pressure equalization is possible. Serving as the inner electrode for the reference chamber 22 is the same punchshape member 19 as in the measuring chamber 16. It carries at the side of the reference chamber 22 a further radioactive preparation 24.

Continuing, it will be understood that the plate member 25 supports electronic components and a printed circuit which evaluates a change in the ionization current in the measuring chamber for sounding an alarm. Once again, a reaction agent-delivering substance 26 is housed in the measuring chamber 16, and specifically, internally of the punch-shaped inner electrode 19. It communicates with the interior of the measuring chamber 16 via openings provided at the wall of the punch-1ike member and is capable of maintaining in the measuring chamber 16 a certain reaction agent-partial pressure. Of course, the re action agent-delivering substance 26 can be located at a different place in the measuring chamber, for instance upon the closure plate 21 or preferably in the region of the openings for the entry of the gas. Furthermore, it is not necessary that the radioactive substances 20 or 24 be located upon the common electrode 19. They can equally well be situated at a different location of the measuring chamber, for instance upon the plate member 21, and instead the ammonia-delivering substance can then be placed at the location of the preparation 20 upon the punch-like member 19 of the inner electrode of the measuring chamber 16.

The described ionization fire alarm has, in the same manner as the described optical the alarm, the characteristic that it responds both to smoke as well as to hydrogen halides in the atmosphere. Since it additionally detects combustion aerosols, which are no longer visible as smoke and therefore cannot be ascertained with optical fire alarms, the ionization fire alarm of the heretofore described type provides a particularly useful constructional embodiment of the invention. It is also particularly sensitive to the reaction aerosols which form aerosols as expressed by the reaction: Reaction agent+hydrogen halide=reaction aerosol forming aerosols.

During the selection of the reaction agent-delivering substance, on the one hand, it should be observed that the vapor pressure at room temperature is high enough to detect early enough the first traces of hydrochloric acid vapors which occur during a PVC-fire. On the other hand, the vapor pressure should not be so high that there oc-' curs an adverse effect upon the surroundings.

Therefore, substances have been found to be particularly suitable for the purposes of the invention where such possess a reaction agent-vapor pressure of maximum 100 torr at a temperature of 20 C.

Additionally, the reaction agent cannot have any appreciable influence upon the normal combustion aerosolsensitivity of the fire alarm. In the case of the optical fire alarm, this means that the reaction agent must be optically neutral, that is to say that it behaves like air.

-With ionization fire alarms the mobility of the ions of the reaction agent in the electric field of the ionization chamber must be in the same order of magnitude as that of the air ions. With larger deviations with respect to the mobility of air ions such must be compensated by a lower partial pressure of the reaction agent.

For instance, the reaction agent can be ammonia gas which is produced from an aqueous ammonia solution by its normal ammonia vapor pressure. Such is already quite considerable at room temperature and with saturated solutions amounts to almost one atmosphere. An ionization chamber in which there is located aqueous ammonia solution is thus primarily filled with ammonia gas and its cur-" rent-voltage characteristic deviates considerably from that which is only filled with air which, in turn, strongly impairs the smoke aerosol-detection sensitivity. Therefore, aqueous ammonia solutions are unsuitable.

Very good results can be obtained if there is selected a substance which only delivers ammonia gas in relatively small quantities to the surroundings. To this end, there are two possibilities. On the one hand, the substance can contain ammonia and possess a certain ammonia vapor pressure. Such substances are, for instance, inorganic heavy metal-complex amine salts. Known representatives of this class are tetraaminecopper sulfate [Cu(NH SO- hexaaminenickel sulfate [Ni(NH SO diaminesilver chloride [Ag(NH Cl], hexaamineiron chloride and so forth. Particularly suitable are salts of nickel and copper.

However, ammonia gas can be produced from certain substances through chemical reactions, whereby there results a slight air moisture or catalytically influencable decomposition. Thus, for instance, small quantities of ammonia gas are slowly formed from calcium cyanamide or appropriate magnesium salts through small quantities of Water vapor in a chemical reaction. Magnesium cyanamide is particularly suitable for the described process.

A completely different group of substances are those which can indeed be chemically derived from ammonia, but themselves do not deliver any ammonia. Thus, it is known that organic nitrogen compounds more or less, depending upon their chemical composition, possess basic properties and tend to form salts with hydrogen halide materials. Also such compounds, when they possess a certain vapor pressure in the air space, together with hydrogen halides in a chemical reaction deliver aerosols which leads to increased detection sensitivity of hydrogen halides.

Very suitable substances are tertiary organic amines, or, for instance, ethylenediamine or dimethylamine.

If the substance is liquidous at room temperature or at the maximum operating temperature which is to be expected, then it is advantageous to embed such in porous supporting material in the measuring chamber.

When using a fire alarm under extreme temperature conditions or with pronounced temperature fluctuations, it is possible to provide an additional electrical heating of the ammonia delivering substance in order to adjust the ammonia vapor pressure. Such additional electrical heating means 50 has been schematically shown in FIG. 2 for example. Such a device can also serve for regulating a predetermined desired sensitivity for hydrogen halides under certain conditions.

It should be apparent from the foregoing detailed description, that the objects set forth at the outset to the specification have been successfully achieved. Accordingly,

We claim:

1. An automatic fire alarm having at least one measuring chamber accessible to the surrounding atmosphere and sensitive both to combustion products such as smoke, and to hydrogen halide vapors and constructed to deliver an alarm signal through the agency of an electric circuit when either combustion products or hydrogen halide vapors or both enter the measuring chamber, said measuring chamber comprising means for detecting combustion products such as smoke, and a substance which over prolonged periods of time continually delivers a reaction agent with a vapor pressure of less than torr at 20 C. and forming with hydrogen halide vapors products having properties similar to and detectable in the same manner as combustion products.

2. The automatic fire alarm defined in claim 1, Wherein said substance is in a solid state.

3. The automatic fire alarm defined in claim 1, Wherein said substance is in a liquid state.

4. The automatic fire alarm defined in claim 1, Wherein said reaction agent is ammonia.

5. The automatic fire alarm defined in claim 1, Wherein said reaction agent is ethylenediamine.

6. The automatic fire alarm defined in claim 1, Wherein said reaction agent is dimethylamine.

7. The automatic fire alarm defined in claim 1, wherein said reaction agent delivering substance is a member selected from the group comprising calcium cyanamide and magnesium cyanamide.

8. The automatic fire alarm defined in claim 1, wherein said reaction agent-delivering substance is located in a porous support material.

9. The automatic fire alarm defined in claim 1, further including an additional electrical heating means located at the region of the reaction agent-delivering substance for adjusting a desired temperature and vapor pressure thereof.

10. The automatic fire alarm defined in claim 1, where in said reaction agent-delivering substance gives 0E ammonia in the presence of a catalyst.

11. The automatic fire alarm defined in claim 10, wherein said reaction agent-delivering substance is a metal cyanamide.

12. The automatic fire alarm defined in claim 1, wherein said reaction agent-delivering substance gives off ammonia in the presence of moisture.

13. The automatic fire alarm defined in claim 12, wherein said reaction agent-delivering substance is a metal cyanamide.

14. The automatic fire alarm defined in claim 1, wherein said reaction agent-delivering substance is a member selected from the group comprising inorganic amines, ammonia and organic amines.

15. The automatic fire alarm defined in claim 14, wherein said reaction agent-delivering substance is an inorganic heavy metal-complex amine salt.

16. The automatic fire alarm defined in claim 15, wherein said inorganic heavy metal-complex amine salt is a member selected from the group comprising tetraaminecopper sulfate, hexaaminenickel sulfate, diaminesilver chloride and hexaamineiron chloride.

(References on following page) References Cited UNITED STATES PATENTS FOREIGN PATENTS OTHER REFERENCES 1. 4 R Merck Index 7th edn., 1960, p. 192. E g? et a X Merck Index 7th edn., 1960, p. 428. 5 Chem. Abstr. 46, 3441e 1952 White et a1 340-237 Derfler 25083.6 FT X MORRIS O. WOLK, Primary Examiner Van Luik, R. M. REESE, Assistant Examiner us. 01. X.R.

S 25Q 83'6 FT 2S0--44, 83.6 FT; 32433; 340-237 Nagai et al., Chem. Abstr. 48, 54120 (1954).

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