GB2139747A - Protecting an enclosure against the ingress of airborne contaminants - Google Patents

Abstract

A method of protecting an enclosure 2 against the ingress of airborne contaminants, comprises chemically generating a breathable gas, preferably oxygen, by igniting a plurality of chemical gas generators 4a-4h in sequence and introducing the gas into the enclosure at a rate greater than the gas leakage rate therefrom at atmospheric pressure. The air within the enclosure may be scrubbed to remove airborne substances therein, by introducing said gas into the enclosure via a venturi tube thereby circulating the air within the enclosure through a scrubber for removing the undesirable substances. <IMAGE>

Description

SPECIFICATION Method and system for protecting an occupant or contents of an enclosure againstthe ingress of airborne contaminants The present invention relates to a method and systernforprntecting an occupant of an enclosure, or the contents of an enclosure, againstthe ingress of airborne contaminants, such as toxic agents, aerosol materials, dust, powder, sprayed liquids, or the like.

There are many applications, such as environmental control rooms, bomb shelters, vehicles, etc., wherein it maybe desirable or essential to preventthe ingress of airborne contaminants. At the presenttime, this is usually done by creating a slight over-pressure within the enclosure from a pressurized gas container and releasing it as required into the enclosure. Such a method, however, has the logistical disadvantage that gas stored under pressure for long periods of time is prone to leakage and therefore must be frequently checked and/or replaced, beside the safety disadvantage that such pressurized gas may cause a pneumatic explosion.

Another method for protecting against the ingress of airbornecontaminantswithin an enclosure is bythe use of blowers. This method, however, has the disadvantage that it requires power, ducts, and filters, all of which involve substantial initial costs as well as maintenance costs. in addition, the filters must be periodically cleaned or replaced, and also must be of a type which is not destroyed by the contaminantto be removed.

An object ofthe present invention is to provide a method and system for accomplishing the above purposes, but having many important advantages over the methods and systems previously used.

According to one broad aspect of the present invention, there is provided a method and system for protecting an occupant or the contents of an enclosure against the ingress of airborne contaminants, characterized in chemically generating a breathable gas by ingniting one or more chemical gas generators, and introducing said gas into the enclosure at a rate greaterthan the gas leakage rate therefrom at atmospheric pressure, whereby an over-atmospheric pressure is produced and maintained within the enclosure by the chemically generated gas.

In one preferred embodiment of the invention described below, the chemically-generated gas is produced by igniting a plurality of chemical gas generators in sequence such that one is automatically ignited afterthe preceding one inthe sequence has been substantially exhausted. More particularly, in the described system, each of the chemical gas generators may be preset according to a STOP, START or AUTOMATIC condition, each generator preset to a STOPcondition being disabled from ignition, each generator preset to a START condition being ignited, and each generator preset to an AUTOMATIC condition being ignited automatically in sequence when the preceding generator in the sequence has been ignited and substantially exhausted.

Following are some ofthe advantages provided by the method and system ofthe present invention in which the over-pressure is created by gas generated from chemical sources: high reliability, as there are presently available chemical gas generators which have very long shelf life and which do not depend upon regulating valves, external power sources, or other special equipment; safety, as there are no vessels under pressure which might explode; universality in application, as the over-pressure may be created in an enclosure of any volume, provided the leakage ratefrom that enclosure is at, or can be reduced to, an acceptable level; flexibility, as the modular nature of gas generators permits their use in series and/or in parallel, according to the desired generation rate; low cost, as high-pressure vessels, regulating equipment, filters, or special installations, are not required; minimum logistics, as the generators may include replaceable cartridges or candles which can be conveniently stored for immediate use when needed; and minimum support, as relatively little inspection or maintenance work is required after istallation.

Furtherfeatures and advantages ofthe invention will be apparent from the description below.

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: Fig. lisa diagram schematically illustrating one form of system constructed in accordance with the present invention; Fig.2 isafragmentaryviewillustrating a partofthe control panel in the system of Fig. 1; Fig. 3 illustrates oneform of actuating mechanism provided for each of the chemical oxygen generators in the system of Fig. 1; Fig. 4 is athree-dimmensional view illustrating the resetting slide in the actuating mechanism of Fig. 3; Figs. 5a-5c illustrate the condition ofthe mechanism of Fig. 3 when preset according to any one of three positions; and Figs. 6-9 illustrate various other applications ofthe invention.

General Construction The system illustrated in Fig. 1 is intended for protecting an occupant within (or the contents of) an enclosure, generally designated 2, againstthe ingress of airborne contaminants. For this purpose, the system comprises a pluralitvofchemical gasgenerators 4a-4h, which may be installed externally ofthe enclosure 2 as shown in Fig. 1, or internally within it.

The gas generators are ofthetype which generate oxygen when ignited, one example being sodium chlorate cartridges or candles. They are all connected by conduits 6a-6h to the next cartridge by conduits 44a-44g and, via check valves 7a-7h, to a distribution manifold block 8, which block is in turn connected to a plurality of distribution ports 1 Oa-l Od within the enclosure. The enclosure 2 further includes a control panel, generally designated 12, having a plurality of manipulatable knobs 14a-14h, each connected buy a push-pull cable 1 6a-16h to one ofthe chemical gas generators 4a-4h.

Fig. 2 illustrates a portion of the control panel 12, wherein it will be seen that each knob, e.g., knob 14a, is rotatable to one of three positions, namely: START, AUTO(MATIC), and STOP. Each ofthe push-pull cables 16a-16h is connected at one end to its respective knob 1 4a-1 4h via a swivel clamp t8 and at its opposite end to an actuating mechsnism 20a-20h provided for each ofthe generators 4a-4h.

Figs. 3 and 5a-5c illustrate one such actuating mechanism 20,wherein it will be seen that the respective push-pull cable 16 is connected to a pivotably mounted enabling fork 30 ofthe actuating mechanism such that when the knob is in the START position, its respective enabling fork 30 is in the position illustrated in Fig. 5a; and when the knob is moved to its AUTOMATIC position or STOP position, its enabling fork 30 is pivoted to the position illustrated in Figs. Sc or Sb, respectively.As will be described more particularly below, manually moving the knob forany particular generatorto the START position (Fig. 5a) effects the ignition of that particular generator; moving the knob to the AUTOMATIC position (Fig. 5c) enablesthe ignition of the respectivegenerator automatically afterthe generator preceding it in the sequence has been ignited and has been substantially exhausted; and moving the knobto the STOP position (Fig. 5b) prevents the ignition ofthe respective generator.

The control panel 12 preferably also includes an indicator22 for each of the generators to indicate whetherthe resepctive generator is generating gas or is exhausted; another indicator 24to indicate whether any ofthe generators is generating gas; and a differential-pressure indicator 26 to indicate the difference in the pressure within the enclosure 2 over the ambient pressure. Thus, if the occupant of the enclosure 2 sees that the differential-pressure within the enclosure is dropping below the desired value, either because the system is not generating oxygen or is generating the oxygen at an insufficient rate, the operator maythen manually ignite another generator by moving its knob 1 4to the START position to cause that generator to start generating oxygen either alone, or in parallel with one or more other generators.Thus the control panel 12 permits a high degree of control of the generators4a-4h for a combination of manual and automatic operation according to the requirements of any particular situation.

Actuating Mechanism The actuating mechanism 20, of each ofthe generators 4a-4h, includes, in additiontothe pre viously-mentioned enabling fork30 coupled to the push-pull cable 16 for the respective generator, an unlatching slide 40 which controls the movement of a spring-loaded hammer arm 50 effecting the ignition of the respective generator; an unlatching hook 60 controlling the position ofthe unlatching slide 40 during certain operations; a locking bar 70 for locking the enabling fork in its START position; and a reset slide80,which slide is depressed in orderto resetthe various elements ofthe actuating machanism 20, all as described below in detail.

More particularly, the enabling fork30 receives the end of its respective push-pull cable 16, the latter being passed through a boreformed in the fork and secured therein by a screw 31. Enabling fork 30 is pivotably mounted at 32so asto be pivotable to any one ofthethree above-mentioned positions as illustrated in Figs. 5a-5e according to the manual setting ofthe control panel knob 14 secured to the opposite end of cable 16. This fork 30 includestwo parallel legs 33 and 34. The inner leg 33 is formed at one end with a cam surface 35 cooperable with the unlatching slide 40, and with a tab 36 cooperable with the unlatching hook 60. The outer leg 34 ofthe enabling fork 30 receives a stop screw 37 cooperable with the opposite face of unlatching hook 60.

Unlatching slide 40, as mentioned earlier, controls the movement ofthe spring-loaded hammer 50 and thereby controls the ignition ofthe respective generator4. The hammer 50 includes an arm 51 pivotably mounted on pin 52 by means of a spring 53 towards the percussion cap 54 (see Figs. Sb, Sc) for impacting same in order to effectthe ignition ofthe respective generator4. The hammer arm 51 isformedwithatab 55 at its lower end, which tab normally engages the unlatching slide 40 to blockthe pivoting ofthe hammer arm when the unlatching slide is in its intermediate position (Fig. 5b) or its retracted position (Fig. 5c). However, when slide 40 is in its extended position (Fig.Sa), its notch 41 is aligned with tab 55, permitting the hammerto impactthe percussion cap 54 and therebyto ignitethe generator. Hammer arm 51 is fixed to a pinion 56which is partially toothed to permit resetting ofthe hammer arm.

Slide40 is coupled to a diaphragm 42 which defines a chamber43 adapted to be pressurized via a conduit 44 bythe previous generator4 in the sequence when that generator is generating gas. Unlatching slide 40 further includes a spring 45 urging the slide to an extended position (Fig. Sa)to align its notch 41 with tab55ofthehammerarm 51, andtherebyto permit the hammerto impact percussion cap 54 (e.g. Figs. 5b, 5c). Thus, the extended position (Fig. 5a) ofthe unlatching slide 40 is the "firing" position ofthe slide.

It is also moved to this position by cam surface 35 of the enabling forkwhen the latter is preset to START (Fig. 5a).

Unlatchingslide40furtherincludesan end flange 48 cooperablewith an arm 61 terminating in a projection 61'carriedatthe end ofthe unlatching hook60.

Unlatching hook 60 is also pivotably mounted to the pivot axis 32 of the enabling fork 30. It is urged counter-clockwise (when viewed in Fig. 3) by a spring 62 interposed between the lower enabling fork leg 33 and the underface ofthe unlatching hook. The upper face ofthe hook is engageable by stop screw 37 carried bythe upper enabling fork arm 34.

Unlatching hook 60 is effective, when the enabling fork 30 is in the STOP position illustrated in Fig. 5b, to blockthe unlatching slide 40 (by engagement with its end flange 46) from moving to the "firing" position (Fig. 5a) ofthe hammer50.

However, unlatching hook 60 also plays an impor tantfunctionwhentheenabling hook30 of the respective generator actuating mechanism is preset to the AUTOMATIC condition, as illustrated in Fig. 5c.

The enabling fork can be preset to the AUTOMATIC condition only from the STOP condition (Fig. 5a), because of thepresence of locking bar 70, as will be described more particularly below. Accordingly, when the enabling fork 30 is moved from the STOP condition (Fig. 5b) to the AUTOMATIC condition (Fig. 5c), the unlatching hook 60 is retained in its Fig. 5b latching condition with respectto slide 40, as shown by the broken lines in Fig. 5c. Thus, in presetting the mechanism to the AUTOMATIC condition, the latching slide 40 remains latched in its intermediate position (Fig. 5b) wherein it blocks the hammer 50 from impacting the percussion cap 54.

However, when the preceding generator is ignited, chamber43 ofthe latching slide 40 assembly is pressurized, thereby moving the unlatching slide 40 to its fully-retracted position, as illustrate in full lines in Fig. 5c; this permits spring 62 to pivot the unlatching hook 60 (counter-clockwise) to the solid-line position illustrated in Fig. 5c. The actuator mechanism is thus released or cocked forfiring, which occurs as soon as the previously-fired generator becomes exhausted.

When this occurs, the pressure within chamber 43 drops causing the unlatching slide 40to move, under the influence of spring 42, to its rightmost (firing) position (Fig. 5a) wherein itunlatchesthe hammer 50, permitting itto impactthe percussion cap 54 and thereby to ignite the generator.

Locking bar 70 is pivotably mounted to a bearing plate 71 and includes a leg 72 at one end cooperable with the unlatching slide 40, and a cam leg 73 at its opposite end, radially offset from leg 72, and cooperable with the enabling fork30. Locking bar 70 is normally urged, by a spring 74, to the position illustrated in Fig. 5a underlying leg 33 offork 30, to lock the fork in its START position, wheneverthe unlatching slide 40 is in its extended firing position (Fig . 5a) in either of the othertwo positions (Figs. 5b, 5c) of the unlatching slide 40, this slide engages leg 72 ofthe locking bar70,thereby preventing it from locking fork 30 in its START position.

The resetting slide 80, as shown particularly in Figs.

3 and 4, comprises a stem 81 passing through an opening in the housing of the actuating mechanism 20. Stem 81 is biased to a normal position, as illustrated in Fig. 3, by means of a spring 82 interposed between the housing of mechanism 20 and an enlarged head 83 carried by stem 81 externally of the housing.

Within the housing, stem 81 ofthe resetting slide 80 carries a number of members which, when the slide is depressedagainsttheaction ofspring82,engagesthe various elements ofthe actuating mechanism to reset them, as follows: Ramp 84 engages the end flange 46 of the unlatching slide 40to reset it; rack 85 engages pinion 56 ofthe hammer 50 to reset it; tab 86 engages the unlatching hook60to reset it; another tab 87 engages the enabling fork 30 to reset it; and a notch 88 engages the locking bar70to reset it.

Operation The illustrated system may be operated as follows: Assuming all ofthe gas generators 4a-4h are full, their respective knobs 14a-14h on the control panel 12 are manually set according to the operation desired.

First, itwill be assumed that all the knobs are in their STOP positions, in which case the condition of each of the actuating mechanisms within housing 20 for the respective generators is as illustrated in Fig. 5b. Thus, in the STOP condition, the enabling fork 30 ofthe respective actuating mechanism will have been moved by its respective push-pull cable 1 6to the substantially horizontal position illustrated in Fig. 5b, wherein screw37 will have moved the unlatching hook 60 to the Fig. 5b position.In this position, arm 61 ofthe unlatching hook engages the end flange 46 of the unlatching slide to hold the slide in the intermediate Fig. 5b position wherein notch 41 of the slide is out of alignmentwith tab 55 ofthe hammer arm 51, thereby preventing the hammer from impacting againstthe percussion cap 54to ignite the generator.

Accordingly, when knob 14 of the respective generator is in the STOP position, the generator cannot be ignited.

Now, ifthe knob l4foranyparticulargeneratoris moved to the START position, the enabling fork 30 for the respective generator is pivoted counter-clockwise to the position illustrated in Fig. 5a. This pivoting of the enabling fork removes its arm 61 from engagement with the end flange 46 ofthe unlatching slide 40, permitting the slide to be moved by cam surface 35 to its projected position (Fig. 5a), wherein its notch 41 becomes aligned with tab 55 of the hammer arm 51.

Thus, the hammer arm 51 is permitted to be driven, by its spring 53, into engagement with the percussion cap 54 to ignite the respective generator.

The movement of slide 40 to its "firing" position (Fig. 5a) also removes it from engagement with leg 72 ofthe locking bar 70, thereby permitting the locking bar to pivot, under the influence of spring 74, to bring its leg 73 underneath the enabling fork 30, and thereby to lock it in this START position. Thus, once a generator is ignited, it cannot be stopped until exhausted.

If knob 14for any particular generator is moved to the AUTOMATIC position,the enabling fork 30 of the respective generatorwill be moved by its push-pull cable 16tothe pivoted position illustrated in Fig. 5c.

However, projection 61 of the unlatching hook 60 is engaged with the end flange 46 ofthe unlatching slide 40so that the unlatching hook assumes the brokenline position illustrated in Fig. 5c.

Now, whenever the generator preceding that particular one in the sequence is generating gas, chamber 43 ofthat particular generator will be pressurized via conduit 44 connected to the preceding generator, so thatunlatching slide 40 will be moved to its retracted position (Fig. 5c), wherein it allows spring 62 to pivot the unlatching hookto the solid-line condition illustrated in Fig. 5c, but its notch 44 is still out of alignment with hammer tab 55, thereby still blocking the firing of the hammer. This is the cocked position of slide 40, and as soon as the pressure from the preceding generator4 drops, the pressure in chamber 42 also drops, thereby permitting spring 45to move the unlatching slide 40 to its Fig. 5a position wherein its notch 41 becomes aligned with tab 55 of hammer arm 51, permitting the hammer 50 two impactthe percus sion cap and to ignite the repective generator.

The movement of the unlatching slide 40 to its cocked position (shown in solid lines in Fig. 5c) also removes it from locking leg 72 of locking bar 70, permitting the locking bar to pivot and to force its other leg 73to move enabling fork 30, to its START position as illustrated in Fig. 5a. This pivoting of the enablingforkalso moves, via its push-pull cable 16, its respective knob 14to the START position so thatthis firing ofthe respective generator, whose actuating mechanism was originally preset to the AUTOMATIC position, is indicated bythe movement ofthe knob to the START position.

As indicated earlier, once the ignition of any particular generator starts, it cannot be stopped until exhausted. However, if a generator is preset to the AUTOMATIC position and, before it starts generating (i.e., before it becomes cocked bytheignitionofthe generator preceding it in the sequence), it is desired to reset itto its STOP position, this can be done by merely moving its respective knob 14from AUTOMATIC to STOP,this being permitted by the locking bar 70 which, in the Fig. 5e (broken-line) position of the unlatching slide 40, is blocked by the latter slide from moving into locking engagement with the enabling fork 30.

Thus, all ofthe knobs 1 4a-1 4h on the control panel 12may be individually presetto any one oftheir respective three positions START, AUTOMATIC, or STOP, Whichever one is set to START, its respective generator is immediately fired (by cam surface 35, Fig.

5a) and generates gas until exhausted, the knob having been locked in the START position bythe locking bar70. If it is desired to fire a plurality of the generators in sequence,thefirstone in the sequence would be set to START, and the others would be set to AUTOMATIC, whereupon the first would immediately fire, and each generator subsequent in the sequence would automatically fire upon the exhaustion of the generator preceding it in the sequence, the sequential firingterminatingforthefirstgeneratorwhose knob l4issettotheSTOP position.

Theflowofthegasfrom any particular generator and from all the generatorstogether, and the pressure within the enclosure 2, are all indicated by indicators 22,24 and 26 on the control panel 12, so that ifthe operator sees thatthe pressure within the enclosure is undesirably low, he can, bythe manipulation of the knobs 14a-14h in the manner described above, fire one or more additional generators, individually, in sequence, or in a plurality of parallel sequences, as desired according to the particular situation. The illustrated system thus provides a high degree of flexibility and control in the manner of igniting the generators.

Replacing Generators and Resetting the Mechanism The generators 4a-4h may be individually replaced and their actuating mechanisms may be reset in the following manner: In orderto replace a generator, the depleted one is removed and a new one applied to the end of its respective conduit 6 leading to the distribution manifold block 8. Resetting slide 80 isthen depressed to resettheactuating mechanism, whereupon itwill return by spring 82.

The depression of reset slide 81 resets the mechanism in the following manner: First, its rack 85 engages pinion 56 to rotate the hammer arm 51 180" or more; this causes the hammer tab 55 to pass through the notch 41 ofthe unlatching slide 40, to thereby position the hammer 50 in its spring-loaded condition.Notch 88 ofthe resetting slide then engeges leg 73 ofthe locking bar70to pivot it againstthe action of its spring 74, out of engagement with theenabling fork 30, while tab 87 engages the enabling fork to pivot it to its STOP position illustrated in Fig. 5b. Also, ramp 84 of the resetting slide 80 engages end flange 46 ofthe unlatching slide 40 to move it leftwardly,whiletab 86 engagesthe unlatch- ing hook 60 to move its arm 61 into engagement with the end flange 46 ofthe unlatching slide 40to hold the latter slide in its intermediate latching position illustrated in Fig. 5b. This movement ofthe unlatching slide removes its notch 41 from alignment with the hammertab 55, thereby retaining the hammer in its spring-loaded condition.

The actuating mechanism for the respective gener ator is thus in its STOP condition (Fig. 5b), which fact is also indicated by its knob 14 on control panel 12 being moved to its STOP position by cable 16. At anytime thereafter, the knob may be manipulated eitherto its START position wherein it ignites the respective generator, orto its AUTOMATIC position wherein it is on standby and automatically ignites its respective generator only when the generator preceding it in the sequence has been fired and has been substantially exhausted, as described above.

OtherApplications and Variations The invention may be used in many other applications, some of which are illustrated in Figs. 6-9.

Thus, Fig. 6 illustrates the invention applied to a pressure suit, generally designated 100,forpersonal protection of an individual, the pressure suit itself being considered as the enclosure corresponding to enclosure 2 in Fig. 1. The suit 100 need be capable of withstanding a pressureonlyslightlyhigherthan atmospheric pressure, and therefore may be made of mass-produced plastic sheeting heat-sealed to a configuration generally conforming to the human form. The suit may be constructed in suitable sections, as shown in Fig. 6, including a head section 102, an upper body section 104 and a lower body section 106.

The upper body section 104 covers the occupant's shoulders,waistand arms, the latter being covered by an extension 104' for each arm to permitthe occupant to grasp articles, etc; and the lower body section 106 coversthe occupant's waist and also includes two extensions 106' to cover each ofthe occupant's two legs so as to permitthe occupantto walk.

The chemical oxygen generator is carried bythe occupant externally ofthe suit 100, as shown at 108, and includesatubeconnection 110 leading into the interior of the head section 102. The latter section includes a circular reinforcement 112 enclosing the neck ofthe occupant and provided with drawstrings 1 14for providing a loose fitting around the occupant's neck. The upper end ofthe upper body section 104 is open and is received within the circular reinforcement 112 of the head section 102. The upper end of the lower body section 106 is received around the lower end ofthe upper body section 104, and is similarly provided with drawstrings 116.Both drawstrings 114 and 116 need only be slightly tightened to permitthe oxygen generated in the chemical generator 108 and fed into the head section 102 via the tube connection 110, to slightly inflate the head section 102 and to leak pastthroughthedrawstrings 114and 116to the upper and lower body sections 104, 106 respectively, thereby also over-pressurizing them sufficiently to prevent the ingress of air contaminants which may be toxic if inhaled or contacted by the occupant.

Fig. 7 illustrates another application wherein the enclosure, therein designated 120, is a small cylinder for receiving a single occupant, such as an infant oran incapacitated person. Cylinder 120 is of rigid or flexible construction, preferably of transparent plastic material, and includes a chemical oxygen generator 122 mounted externally ofthe cylinder, the generated oxygen beingfedtotheinteriorofthecylinderviaa conduit 124. The cylinder may be provided with straps 1 to facilitate carrying it and the occupant.

Fig. 8 illustrates another application ofthe inven tion,wherein the chemical oxygengenerator,therein designated 130, is used not only for over-pressurizing the enclosure, therein desig nated 132, against the ingress of airborne contaminants, but may also be used for removing contaminants already within the enclosure, for example for reducing, or preventing the increase, of carbon dioxide within the enclosure. For this purpose,thechemical oxygen generator130is connected to the interior of enclosure 132 via a venturi tube 134,which produces, atthe location of minimum cross-sectional area of the venturi tube, a pressure belowthe ambient pressure within the enclosure.This pressure-reduction is used fordrawing and circulating the airwithin the enclosure 132 through a scrubber 136 in orderto remove carbon dioxide or other undesirable substances in the air within the enclosure.

Itwill be appreciated that the chemical oxygen generator 130 in Fig. 8 may of course be a pluralgenerator system including a presettable ingnition control as described in Fig. 1 for example.

Fig. 9 illustrates a still furtherapplication ofthe invention wherein the chemical oxygen generator, therein designated 140, may be used not only for preventing the ingress intotheenclosureofairborne contaminants, but may also be used for cooling the air within the enclosure. Forthis purpose, the generator 140 (which may be a multi-unit system as described above) is preferably disposed externally ofthe enclosure 142, and is fed into the enclosure by a conduit 144 having an expansion valve 146 within the enclosure, such that the expansion of the chemically-generated oxygen cools the airwithinthe enclosure. Preferably, the system also includes an air scrubber, designated 150 in Fig. 9, connected to a low pressure producing venturi tube 152 for drawing the airthrough the scrubber so as to clean as well as cool the air.

While the invention has been described with respect to generators using percussion-cap type ignition devices, itwill be appreciated that other chemical gas generators may be used, for example, the type including hypergolic ignition devices. It will also be appreciated that certain features described above can be advantageously used without others, and that manyothervariations, modifications and applications of the invention may be made.

Claims (32)

1. A method of protecting an occupant or the contents of an enclosure against the ingress of airborne contaminants, characterized in chemically generating a breathable gas by igniting one or more chemical gas generators, and introducing said gas into the enclosure at a rate greaterthan the gas leakage rate therefrom at atmospheric pressure, whereby an over-atmospheric pressure is produced and maintained within the enclosure by the chemically generated gas.

2. The method according to Claim 1, wherein said chemically generated gas is oxygen.

3. The method according to either of Claims 1 or 2, furthercharacterized in that said chemically generated gas is produced by igniting a plurality of chemical gas generators in sequence such thatone is automatically ignited afterthe preceding one in the sequence has been substantially exhausted.

4. The method according to Claim 3, wherein the ignition of each chemical gas generator in said sequence is automatically initiated by sensing the drop in pressure when its preceding chemical gas generator has been substantially exhausted.

5. The method according to eitherofClaims3 or4, wherein each ofthe chemical gas generators is preset according to a STOP, STARTorAUTOMATIC condition, each generator preset to a STOP condition being disabled from ignition, each generator preset to a START condition being ignited, and each generator preset to an AUTOMATIC condition being ignited automatically in sequence when the preceding generator in the sequence has been ignited and substantially exhausted.

6. The method according to any one of Claims 1-5, wherein the enclosure is one to be occupied by a plurality of persons.

7. The method according to any one of Claims 1-6, wherein the gas is chemically generated within the enclosure itself.

8. The method according to any one of Claims 1-5, whereinthe enclosure is in theform of an outer garment made offlexible sheet material to be occupied by a single person.

9. The method according to any one of Claims 1-5, wherein the enclosure is a small portable unit to be occupied by a single individual.

10. The method according to any one of Claims 1-9, wherein the air within the enclosure is also scrubbed for removing substances therefrom, by passing the gas from the generatorthrough a venturi tube to produce a pressure drop therein, which pressure drop is utilized to circulate the air within the enclosure through an air scrubber.

11. The method according to any one of Claims 1-10, wherein the airwithin the enclosure is also cooled by locating the chemical gas generator externally ofthe enclosure and expanding the gas intro duced into the enclosure.

12. A system for protecting an occupant or the contents of an enclosure against the ingress of airborne contaminants, characterized in that said system includes one or more chemical gas generators for generating a breathable gas and for introducing same into the enclosure at a rate greater than the gas-leakage rate from the enclosure at atmospheric pressure,wherebyan over-atmospheric pressure is produced and maintained within said enclosure by said chemically generated gas, in use.

13. ThesystemaccordingtoClaim 12,wherein said chemical gas generators are sodium chlorate candles generating oxygen when ignited.

14. Thesystem according to either of Claims 12 or 13, wherein there are a plurality of chemical gas generators, the system further including ignition control means for igniting generators in sequence automatically upon the substantial exhaustion ofthe generator preceding it in the sequence.

15. Thesystem accordingto Claim 14, wherein said ignition control means comprises: a presettable memberfor each chemical gas generatorfor presetting same to one of a plurality of positions, including STOP, START or AUTOMATIC: and an actuating mechanism for each chemical gas generator effective to disable its respective generator when presettothe STOP position, to ignite its respective generator when preset to the START position, and, when preset to the AUTOMATIC position,to cause its respective generatorto be automatically ignited afterthe preceding generator in the sequence has been ignited and has become substantially exhausted.

16. Acontrol systemforcontrollingthe ignition of a plurality of chemical gas generators, comprising: a presettable memberfor each chemical gas gener ator,which member may be presetto one of a plurality of positions, including STOP, START or AUTOMATIC; and an actuating mechanism for each generator effective to disable its respective generator when preset to the STOP position, to ignite its respective generatorwhen preset to the START position, and, when preset to the AUTOMATIC position, to cause its respective generatorto be automatically ignited after the preceding generator in the sequence has been ignited and has become substantially exhausted.

17. A system according to either of Claims 15 or 16 wherein each of said actuating mechanisms includes: an enabling member displaceable to one of th ree positions by its presettable member; an ignition device; a hammerspring-biasedto impact said ignition device in orderto initiate ignition of the respective generator; and unlatching means normally retained by said enabling member in its first position latching said hammerfrom impacting the ignition device, but moved by said enabling member, when in its START position, to a second position wherein it unlatches the hammer and permitssametoimpacttheignition device.

18. Thesystem according to Claim 17,wherein said unlatching means further includes pressuresensing meansforautomatically moving the unlatching means to its unlatching position when its enabling member is preset to the AUTOMATIC position and its pressure-sensing means sences that the preceding generator in the sequence has been ignited and is substantially exhausted.

19. Thesystem according to Claim 18,wherein said unlatching means comprises a hook controlled by said enabling member, and a slide controlled by said hook, such that when the enabling member is preset to the AUTOMATIC position, the hook latches said slide in positionto blockthehammerfrom impacting the ignition device until the preceding generator in the sequence is ignited, whereupon the pressure increase produced thereby releases saidhookfromthe latching slide, so thatwhen the preceding generator is exhausted, the resulting pressure drop causes said slide to unlatch the hammer andto impact the ignition device.

20. The system according to any one of Claims 17-19 wherein said enabling member comprisesarsì enabling fork pivotable by its respective presettabie memberto one of said three positions.

21. Thesystem according to anyone of Claims 17-20, further including locking meansforlockingsaid enabling member in the START position.

22. The system according to any one of Claims 15-21 further including a reset slide which, when depressed, resets all the elements of the actuating mechanism.

23. The system according to any one of Claims 14-22 further including a control panel having a gas flow indicator for each chemical gas generator to indicate gasflowtherefrom into said enclosure.

24. The system according to any one of Claims 14-22, further including a control panel having a gas flow indicator for indicating the flow of gas into said enclosure from any chemical gas generator.

25. The system according to any one of Claims 14-22, further including a differential-pressure indicator indicating the pressure within said enclosure in relation to the outside ambient pressure.

26. The system according to any one of Claims 12-15, wherein said enclosure is one to be occupied by a plurality of persons.

27. The system according to Claim 26, wherein the gas is chemically generated within the enclosure.

28. The system according to any one of Claims 12-15, wherein the enclosure is an outer garment made of flexible sheet material to be occupied by a single person.

29. The system according to any one of Claims 12-1 5,wherein the enclosure is a small portable unitto be occupied by a single person.

30. The system according to any one of Cairns 12-15, further including a venturi tube betweenthe generator and its outlet within the enclosure for producing a pressure drop with respecttotheambient pressure within the enclosure, and an air scrubber within the enclosure and connectedtesaidventuri tube so as to utilize the pressure drop in the venturi tube for circulating air from the enclosure through the air scrubber.

31. The system according to any one of Claims 12-1 5,further including an expansion valve through which the generated gas isfed within the enclosure, to thereby also cool said enclosure.

32. A method as claimed in any of claims 1 to 11, or a system as claimed in claim 12 or in any claim appendantthereto, or a control system as claimed-in claim 16 or in any claim appendantthereto, substan tially as herein described with reference to and as shown in the accompanying drawings.