BACKGROUND ART In view of the high risk to human life that exists when firefighters enter dangerous incidents such as house fires, the fire service currently operate a system that attempts to ensure that firefighters wearing breathing apparatus who need to enter the dangerous area are supervised throughout the incident.

More particularly a breathing apparatus control board (BACB) is set up outside the building to be entered near to the point of entry to the building, the board being under the control of a breathing apparatus entry control officer (BAECO). Every firefighter who wears breathing apparatus at the incident must check in and check out through an entry control point of which there may be more than one.

Every breathing apparatus wearer has a tag or tally attached to their breathing apparatus set which carries information relevant to the wearer and to the set. This tally is removed by the wearer prior to entry to the incident, and is handed over to the control officer.

The basic principle of the current system is that the control officer enters the 'time in' on the tal-ly, and then calculates the time that the firefighter is due out, which is based on the condition of the breathing apparatus at the time of entry. The time out, or whistle time, is entered onto the control board alongside the relevant tally, together with other information such as the anticipated location of the firefighter in the building and the point of entry to the building.

Control boards commonly include a clock, a cylinder duration table and/or a manual calculating device which can be used to determine the safety whistle time, or time out, based on the time in and the volume and pressure of air within the or each cylinder at the time of entry.

Such a system suffers from a number of disadvantages.

Breathing apparatus wearers pass through the system at different times and with different quantities of air in their cylinders. Consequently the whistle times, which must be accurate, vary greatly. The fact that the whistle times have to be calculated manually means that human error can arise from time to time.

Experience has shown that, even during normal practice sessions in a drill yard, mistakes have occurred which could have cost lives. Clearly this is even more likely to happen in real life, high stress conditions.

The problem is compounded by the number of variables that have to be taken into account by the control officer in his calculations - in particular that hard work and very hot conditions could result in the available air being used more quickly - and the fact that the officer must continue to supervise the firefighters during his calculations.

Furthermore, the tables on the control board available to the control officer for calculation purposes will relate only to breathing apparatus sets of a given type within a given duration range. Thus it is not possible to use these tables for breathing apparatus wearers with different cylinder capacities on the same control board.

SUMMARY OF THE INVENTION It would be desirable to be able to provide a display system capable of giving an accurate display of information and from which has been substantially eliminated any possibility of human error.

According to the present invention there is provided an electronic display system comprising a board having a plurality of slots therein each adapted to receive a tally, and a display panel associated with each slot, characterised in that each slot includes therein a plurality of preprogrammed electronic sensors for actuation in dependence upon the volume of, and pressure within, one or more associated compressed air cylinders, and a plurality of tallies each associated with one or more compressed air cylinders, each tally including a plurality of actuating members thereon the positions of which are adjustable in dependence upon the volume of, and the pressure within, the or each associated compressed air cylinder, the arrangement being such that, prior to insertion of a tally into a slot in the board, the positions of the actuating members on the tally are adjusted to indicate the volume of, and pressure within, the or each cylinder, the tally is then inserted into the slot such that the actuating members actuate the sensors associated with said volume and pressure, and the associated display panel indicates the time available to a user of said cylinder or cylinders, said display being programmed in dependence upon the sensors actuated by the tally.

It will thus be appreciated that the preprogramming of the system, and in particular the time out or whistle time of the display, in dependence upon the inputted information relating to the breathing apparatus set, eliminates the possibility of human error in calculating the time available to a user of the equipment.

In a preferred embodiment of the invention, each tally has a fixed actuating member associated with the type of cylinder being used, and indicative of the normal capacity and maximum pressure within that cylinder. Thus the combination of this permanent actuating member, together with the adjustable actuating members one of which is positioned to indicate the number of cylinders and the other of which is positioned to indicate the pressure within the or each cylinder, provides a display indicative of the time available to a user.

Conveniently each tally includes a first table thereon detailing the alternative capacities of the or each cylinder, a second table thereon detailing the range of starting pressures within the or each cylinder, a first slide member associated with the first table and movable relative to the tally to positions indicative of the working capacity of the or each cylinder, and a second slide member associated with the second table and movable relative to the tally to positions indicative of the starting pressure within the or each cylinder, the slide members each carrying an associated actuating member for actuating the relevant sensor on the board.

Preferably each display panel is programmed to indicate, either separately or in combination and at any given time, the anticipated safe time out for the user, the time remaining before the safe time out is reached, the amount of compressed air used and the amount of compressed air remaining.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an electronic entry control board according to the invention, and the direction that a tally is inserted; Fig. 2 shows a known breathing apparatus control board, and the position upon which the electronic entry control board of the invention would take; Fig. 3 shows in more detail the top section of the electronic entry control board of the invention before a tally is inserted; Fig. 4 shows the front face of a tally and its litre and bar windows separately; Fig. 5 shows a top view of the tally, and the litre and bar windows separately; Fig. 6 shows the back of the tally, and the litre and bar windows separately; Fig. 7 shows one end of the tally to which a key ring is attached; Fig. 8 shows the other end of the tally which is inserted into the electronic entry control board; Fig. 9 shows a tally, which would be used for a breathing apparatus set which uses cylinders with 1800 litres of air, charged at 300 bar, and can use up to two cylinders; Fig. 10 shows a separate drawing of the litre window; Fig. 11 shows a separate drawing of the bar window; Fig. 12 shows the top section of the electronic entry control board, after a tally has been inserted into one of the slots; Fig. 13 shows what buttons are being pressed by the tally in Fig. 12.

Fig. 14 shows nine shaded buttons, which define the cylinder type and an on' button for the relevant display; Fig. 15 shows ten shaded buttons, which define the pressure display; Fig. 16 shows two shaded buttons, which define the litre display; Fig. 17 shows fourteen shaded buttons, which define the tally identity display; Fig. 18 shows the top section of the electronic entry control board, and what is displayed when the "Gauge Reading" button is pressed, nineteen minutes after the tally was inserted; Fig. 19 shows the top section of the electronic entry control board, and what is displayed once the "Safety Time" has been reached; Fig. 20 shows the front face of a "Memory/Clear" tally; Fig. 21 shows the back of the "Memory/Clear" tally; Fig. 22 shows a top view of the "Memory/Clear" tally; Fig. 23 shows a type of tally that could be used with a breathing apparatus set which uses cylinders with 1800 litres of air, charged at 300 bar, but can only use one cylinder at a time; Fig. 24 shows a type of tally that could be used with a breathing apparatus set which uses cylinders with 1800 litres of air, charged at 200 bar, and which can use up to two cylinders; Fig. 25 shows a type of tally that could be used with a breathing apparatus set which uses cylinders with 2250 litres of air, charged at 200 bar, and which can use up to two cylinders; Fig. 26 shows the electronic entry control board with two tallies in place, and Fig. 27 shows a side elevation of the electronic entry control board from the side into which the tallies are slotted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, the illustrated electronic entry control board 1 is designed to be a battery, or battery and solar 3 powered, self-contained unit, which will be attached to, and form part of, a known breathing apparatus control board 15, and will accept and display information taken from specially designed tallies 10.

This is achieved by means of buttons 19a-19e on the electronic entry control board 1 being pressed by raised nibs 21a-21e on the underside of each tally 10, when the tally 10 is slotted into the board 1.

From preset known formulae, programmed into the memory of the electronic entry control boards 1, it will automatically calculate, and display in count-down format, both the working time left 25, and the safety whistle time 37 of the cylinder/s for that particular type being used.

Each type of cylinder will be represented by its own coded tally 10, which will have its own set pattern of permanently fixed nibs 21b.

The electronic entry control board 1 will display, the "Time In" 26 the "Whistle Time" 27, the "Minutes Used" 28, the "Tally No." 29, and the expected amount of "Air Used" 32/34.

All the information will be displayed on a known liquid crystal display 8, or similar, and each tally 10 will have its own L.C.D. 8 adjacent to its slot 6 in the board 1.

The electronic entry control board 1 can be made of a plastic material, with plastic or rubber buttons 19a-19e and have the following features: a battery back up, and low battery warning system; water resistant; be permanently marked with words 18 such as those shown in Fig. 3; have holes, or similar, to allow fixing to known breathing apparatus control boards 15; The board may consist of the following: a main digital 24 hour L.C.D. clock 2, preferably of the known radio controlled type, so that every breathing apparatus control board 15 at any one incident displays the exact time; a button 5 to illuminate the main clock 2, and any of the L.C.D's 8 being used; a known electro-luminescent back light, or similar, powered preferably by the battery of the electronic entry control board 1, or by attaching an external battery source, possibly of the rechargeable kind; a suitable external connection point (if necessary) for connection to an external battery; a button 4 to change the normal display 25, to the gauge reading display 31; a solar panel 3, (if necessary); twelve slots 6, one for each tally 10, each slot having a known spring-ball catch 20, or similar for securing the tally 10 in place.

Each slot 6 contains the following buttons 19a-19e: Button l9a, in Fig. 14, the "On" button, which can only be pressed by one projecting nib 21a, which all tallies 10 will have permanently fixed thereto. This button 19a is located in such a position as to ensure that the tally 10 must be fully inserted before the functions of all the other buttons 19b-19e can be activated. This ensures that all the other nibs 21a-21e are in their correct positions before the L.C.D. 8 relevant to that tally 10 is switched on, and the information calculated, thus preventing any calculations taking place when the nibs 21a-21e on a tally 10 pass over buttons 19b-19e, other than the ones that they are meant to press.

Shaded buttons 19b, in Fig. 14, the cylinder type buttons. One, two or more may be pressed at any one time, providing many possibilities for the different types of cylinders, and their durations.

The tallies 10 have permanent nibs 21b located in such positions so as to press the relevant button/s 19b. For example, the tally 10 in Fig. 6 is for a breathing apparatus set which uses cylinders with 1800 litres of air charged at 300 bar.

The tally 10 has a single nib 21b, which is positioned so as to press the button 19b5, in Fig.17.

The electronic entry control board 1 knows from its preset memory that, if the button 19b5 is the only cylinder type button 19b pressed, then the set being used uses one or two cylinders, with 1800 litres of air charged at 300 bar, and therefore can now adjust all the other litre 19d, and bar 19c buttons to coincide with the tally 10 from that particular set.

This enables many different breathing apparatus sets to use the same breathing apparatus control board 15, either with their own kind, or with others.

Shaded buttons 19c, in Fig. 15, the bar buttons. Each tally 10 has a nib 21c fixed to the underside of a moveable bar selection window 12 which, once positioned, will cause the nib 21c to press one of these buttons 19c. The value of each button is determined by the cylinder type button/s l9b already mentioned.

From this, and from which "litre" button 19d is being pressed, the "Whistle Time" 27, the "Working Time Left" 25, and the safety duration 37 can be displayed, using known formulae. For example, Fig. 3 shows the top section of the electronic entry control board 1, without any tallies 10, and displaying the time 12:23 referenced 2.

Fig. 12 shows the same section of the board 1, after a tally 10 has been inserted. Note that the exact time the tally 10 was inserted into the board 1 is recorded as the "Time In" 26, from the main clock 2, and that thirty five minutes (from the known formulae) has been added, and 12:58 recorded as the "Whistle Time" 27, along with the word ENTER, and a flashing, or moving arrow 36, to prompt the person in charge of the board 15 to enter the "Whistle Time" in the space 7 provided as part of the back up. Also note that the large digits 25 have started counting down the thirty five minutes, and the words WORKING TIME LEFT 25 are displayed. Fig. 19 shows what is displayed when the "Working Time" 25 has elapsed, and the "Whistle Time" 37 reached. Note, the words now displayed are WARNING LOW AIR 37. This will flash, and an audible warning will also be given. The time that has elapsed is displayed, as "Mins.

USED" 28, to eliminate the need for any mental calculations, and to give a constant update of time used, for such events as an early exit for decontamination procedures.

Shaded buttons 19d, in Fig. 16, the "Litre" buttons.

The tallies 10 from breathing apparatus sets that use more than one type of cylinder, or can use cylinders of different capacities, will have a nib 21d fixed to the underside of the moveable litre selection window 11, which, once positioned, will cause the nib 21d to press one of these buttons 19d, the value of which is also determined by which cylinder type button/s 19b is being pressed.

Shaded buttons l9e, in Fig. 17, the tally identity buttons. A tally 10 may have one or more permanent nibs 21e positioned so as to press one or more of these buttons 19e, allowing the possibility of hundreds of different combinations, to give each tally 10 its own individual number.

The electronic entry control board 1 would have two other buttons 4/5: The "Gauge Reading" button 4 which, while pressed, will change the normal display 25 to a display 31 showing a pressure gauge, which would look similar to the actual gauge on the set being used. The pressure gauge 31 displayed in Fig. 18 shows the pressure reading 30 that would be required, if the breathing apparatus wearer was on course for his/her "Whistle Time" 27, and was breathing the air at a constant rate.

Although the air consumed by each individual will vary, and gauge readings obtained from the wearers will differ, the display 31 would give a good indication as to how quickly the air was being used.

The shaded section 34 of the gauge shows how much air has been used, and at a glance can be compared with the section 35 which is unshaded to see if the air used section 34 is smaller or greater than the air left section 35.

The expected amount of "Bars Used" 32, and "Bars Left" 33 are also shown, with numbers for accurate reading.

The light button 5, when pressed, would switch on the back light for the main clock 2, and all the L.C.D's 8 which are in use, and, when pressed again, would switch these lights off. When the button 5 is pressed, and no tallies 10 are in the board 1, the back light of the main clock would operate for a few seconds, then switch off.

The tallies 10 will be similar to known tallies, and will provide all the necessary spaces to allow the known details to be filled in. But the "Litres", and "Bars" will be replaced by moveable windows 11/12. This still allows the wearer to enter the information, and also allows for quick adjustment, for example when it is necessary to add another cylinder, or when the pressure in the cylinder has dropped.

A small recess 24 on the side of the tally 10 for the spring-ball catch 20 will ensure the correct position of the tally in the board 1.

A few examples of different tallies 39/40/41 are shown in Figs. 23, 24 and 25, all of which could be used in the same electronic entry control board 1, even at the same time.

Note that the tally 39 in Fig. 23 has no litre selection window 11, because the breathing apparatus set does not use more than one cylinder at a time. A permanent nib could be fixed in the 1800 litre position, if the tally 39 was to use the same cylinder type button as the tally 10 in Fig. 4, or no nib in any of the litre positions if the tally 39 was to use another "Code".

Tallies 10 could be made of yellow, strong rigid plastic, or similar material, with the permanent nibs 21a/21b/21e formed as part of its main structure. The selection windows 11/12, could be of resilient metal, or strong plastic, or similar, with a window 22 fitted with or without a known magnifying glass material. They should be easy enough to move by hand, but not so easy as to become dislodged, for example when slotted into the electronic entry control board 1.

If time permits, the "Time In" must be entered onto the tally 10 in the space 10a provided, as a back up in case of total system failure. It should be done in most cases, before the tally 10 is inserted into the board 1, but can be done at the earliest opportunity. The electronic entry control board 1 would be programmed to allow the removal of the tally 10 for, say, around two minutes without affecting any information on the L.C.D. 8, which would continue as if the tally 10 was still in place, but would only display the "Tally No." 29, "Time In" 26, and the word TALLY would flash every few seconds or so.

This would make the person in charge of the board 15 aware that the tally 10 had been removed, or had become dislodged.

If the tally 10 is replaced within two minutes, everything would continue as normal, unless the wrong tally 10 was replaced in which case the word ERROR would be displayed. If the tally 10 is not replaced within two minutes, this would be classed as the "Time of Exit" for that person, and the L.C.D. 8 would revert back to, and display, all the information that was displayed at the exact moment that the tally 10 was removed.

This safety feature would allow the tally 10 to be removed, and the "Time In" 10a entered (if it had not already been done), to prevent the loss of information if the tally 10 was accidentally removed or dislodged in any way.

Another special tally 38 that can be used with the electronic entry control board 1 is a "Memory/Clear" tally 38, which, when inserted into the board 1 in one direction, will clear the information, and switch off the relevant display. When the tally is inserted in the opposite direction, it will recall the information that was displayed when the last tally 10 was removed. This can be achieved by the tally 38 having permanently fixed nibs 21c1/21c2 in such positions as to press a certain pattern of buttons l9b-19e that would not normally be pressed by any other tally 10.

The electronic entry control board 1 would be programmed to recognize the pattern of buttons 19b-19e being pressed. The tally 38 in Fig. 21 shows an example of how the nibs 21cl/21c2 can be positioned so as to make use of the "Bar" buttons 19c. Note three different "Bar" buttons 19c are pressed for each function.

Although the electronic entry control board 1 will accept, and display, information from any of the specially designed tallies 10 from a large variety of different breathing apparatus sets, it may still be necessary, in order to use the known traditional system as a back up, to use a portable cylinder duration card or similar when the breathing apparatus control board 15 being used does not cover the duration tables for that set.

The electronic entry control board 1 should be fixed to the breathing apparatus control board 15, sandwiched between a clear plastic cover, and a backing board.

Some situations may require the breathing apparatus wearer to re-enter an incident for a small task. When it is not part of the initial entry, a re-entry will be made onto the breathing apparatus control board 15, and fresh records made for that entry. In the case of a cylinder pressure being less than that covered by the tally 10, it may be necessary to use another tally specially designed for the purpose of re-entries, and which would cover the lower pressures that may be used.

A few of these tallies, along with the "Memory/Clear" tally 38, would be kept by the person in charge of the breathing apparatus control board 15. Alternatively, the tallies 10 could be designed to accommodate more cylinder pressures, using the same principles already described.

Another option could be for the bar selection window 12 on the tally 10 to be moved into a central position, so that none of the "Bar" buttons 19c are pressed, and the electronic entry control board 1 could be programmed to recognise this as a re-entry, and only display the "Tally No." 29, "Time In" 26, and the word RE-ENTRY. This would allow the person in charge of the board 15 to calculate the "Whistle Time" using the known traditional system.

Some or all of the nibs 21a-21e on the tallies 10, and the buttons 19a-19e on the electronic entry control board 1 could be replaced by known bar codes, and bar code readers, or similar.

The back light could be of the known automatic light sensitive type, which would activate in poor lighting conditions.

Other modification and variations will be apparent to those skilled in the art.