Modern Fire Alarm Signalling

E. W. KEIRSTEAD
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Modern Fire Alarm Signalling

Planning an Industrial Fire Alarm Installation—Box Locations and Numbers

THIS, the twenty-third article on fire alarm subjects, concludes the series of articles by Mr. Kcirstead on “Modern Fire Alarm Signalling.”

Protection for Small Plants:

Every small establishment should have at least one standard type municipal box installed on their premises, as near to the main gate or entrance as is possible. This box should be connected to the city or town alarm system. This box should be assigned a special number to denote its location, and while it will have to be purchased by the firm owning the factory or building it should be maintained by the city fire alarm department and not by the companies employers.

The private box protection can be increased by the uses of auxiliary pull stations which may be located on each floor. The pulling of this box will set the master box in operation and the alarm will be sent through to headquarters without leaving the building. Thus with a multiplicity of auxiliary boxes it is possible to send alarms from several points.

Fig. 63. Industrial Type Fire Alarm Box

There are two systems which may be used to a good advantage in large and small plants, situated in the department service area: a system which will call the outside department whenever a box is pulled in the plant; a system which will call out the factory brigade when a box is pulled, leaving the calling of the cities forces to the plant fire chief through a manual means of operation.

With the first, it is simply necessary to pull the box in the building and then instruct the fire department as to the location of the fire upon their arrival.

In the other plan a city box is installed at the main gate, power house or office, where a watchman or engineer is constantly on duty. The watchman is instructed to await orders when an alarm is received over the plant system. There will be at least one city box installed at this point and upon the orders of the plant chief, the city box will be pulled, and the department directed to the scene of the fire. Where there are several entrances at the plant, it is well to have a box for each gate and have special numbers given to each box.

Where a plant is located away from the city department the latter system may be used to advantage, as it will be possible to organize a plant brigade, and provide for drills and tests to be made at intervals. Where this system is used the city box is to be used for alarm service only. The boxes used should be of the non-interfering type and be numbered properly in order to get the best possible use from them.

Type of Boxes, Location and Numbering:

When planning a layout for a system use enough boxes so that the floor area to be covered will not make it necessary to travel more than three hundred feet in any direction to reach a box. Have a box at each stair way or entrance, and have them placed so that it will not be necessary to travel away from a natural exit to reach a box. It will fee necessary to take into consideration any special hazards that may exist. Have the boxes standard in their location, that is, in tfee same position on all floors, and have a list of the boxes posted over every box.

Care should be taken at all times to have the approach to a box clear of all obstructions and a red light should be provided at the location at night. Large plants should be well supplied with boxes and special attention should be given to railroad tracks, bridges, etc., to see that it will be possible to reach the box if the way is blocked by a train or the bridge is removed.

Boxes should be numbered according to floors and direction. For example with three number boxes, the first number is the location of the box. such as wing number, plant number or storehouse number. Where there are seven buildings in the property, allow the first number for each one of the buildings. The second number should be allotted to floor on which the box is located. The last or remaining number can be given as the box number. For instance box number 374 would be interpreted as a box located in building three and located on the seventh floor. In figure No. 63 is a type of industrial box.

Gongs and Sounding Devices:

The best type of gong to use in an industrial installation are electro-mechanical gongs. These gongs are placed directly in the box circuit, and are operated by the box itself. The only objection to these gongs is that they will have to lxkept wound up at all times. They should be of a size large enougfe to give a good clear signal above all other noise. They should if possible be located directly over the alarm boxes.

The best type of gong to use is the turtle gong illustrated in Figure No. 64. It may be mounted on the wall or on a panel, and special care must be taken to make sure that the binding posts are upright as this gong depends upon gravity action to drop the hammer.

Switchboards and Battery Energy:

In all types of fire alarm work it is necessary to use duplicates sets of batteries—it is also true in industrial work. One set is charged on the working side of twenty-four hours and then the other Sank or side is shifted into its place.

To control the system a storage battery controlling switchboard is used. It is equipped with the necessary switches, etc., for charging and controlling the batteries. These boards are made up in, one-, two-, four-, six and ten-circuit capacity. It is only possible to place twelve boxes on any one circuit, so if you have forty-eight boxes it will be necessary for you to get a four circuit board. There were two articles given on storage battery switchboards and it will be well to refer to them as much as possible when planning any type of industrial installation.

Fig. 64. Turtle Gong

If the factory has not direct current available, it will be necessary to have a motor generator set to charge the batteries. The size of the generator can be obtained by refering to article No. 23.

F. I. P. batteries are the best type to use as they were especially designed for fire alarm signal work and will give excellent service with a minimum amount of attention. Their capacity is 6-ampere hours and they are discharged at the rate of 1/10-ampere an hour. In twenty-four hours the rate of discharge will be 2.4 amperes.

Drills:

It is a simple matter of wiring to obtain the following results when a box is pulled for fire.

Call the public fire department.

Call the plant brigade to the location of the fire.

Sound the signal only in the building or place afire.

Sound the signal throughout all buildings and call the plant and city department.

The wiring plan may be arranged so that a drill may lx* had in any building at will, without calling the plant or city department.

Where building or floor drills are held, it is very important that the system be SO arranged that if a box is pulled for an actual fire the drill feature will be automatically cut out and the alarm sent through. This is necessary in order to avoid confusion and delay.

When planning any installation it would be a good move on your part to call in the local alarm superintendent as he will no doubt be able to give you the benefit of his knowledge. He will be able, from past experience to offer many suggestions.

New Station Opened in Birmingham, Ala.—-The first of the five new fire stations which are being built in Birmingham, Ala., has been officially placed in service.

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Modern Fire Alarm Signalling

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Modern Fire Alarm Signalling

Some Essentials in Fire Alarm System Layouts; Selection of Materials and Equipment

THIS is the twenty-second of a series of articles on the care, installation and repair of various phases of fire alarm work. In this installment are described some of the essential points which must be considered in the designing of a fire alarm system.

When a new installation is decided upon, it is a common mistake to take too much of the planning and engineering work for granted. As a modern fire alarm system is mainly of a electrical nature, a great deal of planning and preliminary work must be done before the appropriation is asked. Where a rough survey is made and then the money granted as it is oftentimes the case, the system is left without some important feature. After the money for the system is once allowed, it is very hard to get an extra appropriation to cover minor or major changes from the first design.

It is necessary to first, have a good overhead or underground alarm circuit before the alarm system will function, and as the alarm circuits are the nerves of a fire alarm system they will be here given attention.

There are several types of overhead construction now available, anyone of which are suitable for fire alarm work, If the city will stand for a medium first cost on line construction, it will be well to select good cable suspended by messenger cable. There are several reasons why this type of construction is satisfactory, among which are: ruggedness, compactness, and ability to stand heavy weather (such as sleet, snow and rain storms, gales and high winds, etc.); it takes up less space on a pole and allows easy access to other lines. In this type of construction cable or terminal boxes are used. They allow future additions to the circuit as well as providing numerous testing positions. In article No. 1 of this series, line work was taken up in detail and reference to this issue will give additional information.

Assuming that we are laying out an installation where new circuits are to be installed, the line will have to be located where it will be possible to reach points in all directions from its main branch or trunk. If we will stop and visualize the rapid growth of the city or town in many cases we will be able to install a line that will serve our purpose now and also provide central terminal points for future additions. This will incur additional expense, but in two or three years time it may save an expense several times as great. Remember, it does not cost any more for the construction of a twenty pair cable than for a thirty pair cable except in the cost of the cable itself. When placing cable or open work wiring on the poles, always keep in mind that the better grade of materials you use the longer the life you will obtain from the installation. Lines should be placed on the poles with a reasonable amount of slack, especially on lines that are not suspended in rings.

The Overhead Circuit

In overhead circuits it is possible to have twelve boxes on one circuit. On underground circuits as many as twenty boxes may be placed on one circuit, though it is better practice to have fewer than these on the circuits so that additional boxes may be added if needed. Provide as many terminal boxes as possible in order to facilitate easy extension of circuits.

Underground circuits as a rule are run in the telephone companies ducts, and in some cases they supply the cable and pull it in and then charge the city a certain rate. Where it is impossible to get this done, a good grade of cable should be obtained and competent workman engaged to pull in the cable and place it in commission. Failure to secure good workmanship may result in later trouble.

Overhead Construction Materials

A list of the different kinds of materials used in overhead circuit construction is given below:

Cross arms, from 2 to 10 pin.—Good quality of pine, cypress, or other kinds of hard wood. Must be as free from knots and flaws as possible.

Wire suspension brackets.—Should be of heavy duty type. Must be treated or galvanized to protect them from weather.

Messenger wire.—Should be seven or eleven strand wire, galvanized and free from kinks and weak spots. Must all be of equal diameter.

Wire for exterior work.—Should be double braid weatherproof, of equal diameter and have a good grade of rubber covering.

Cables for exterior work.—Should have a good grade of weatherproof covering in addition to the above for open wire.

Glass, pins, toe lags, etc.—Should all be of standard grade and free From flaws.

Alarm Boxes

In importance second only to circuit wiring are alarm boxes. The boxes should be selected with the greatest of care. According to the Underwriters rules only 12 boxes can be placed on an overhead circuit and 20 on an underground circuit.

According to the best practices, heavily populated districts should have boxes placed at least one to a block. If this is not possible allow boxes to be placed so that they can be readily seen from any position on any street.

The non-interfering, succession box is the best type to use in such a district and this type should be installed in preference to any other. The cost of this box is a little more than others, but will hold its own in any kind of mix ups such as incidental to several boxes being pulled at the same time.

Get as many boxes as is possible to start your installation and keep adding as many as you can every year. It is good practice to get a specified number of boxes allowed in your yearly budget. All special hazards must be well protected, such as public schools, hospitals, public homes, theaters, factories, mills, and any other place where large numbers of people are congregated. It is good practice to have a special box on each of the above mentioned places. A great number of cities are already alloting boxes for this purpose.

Schools and hospitals are taken care of by the city. Private plants or factories may be encouraged to purchase boxes outright and have them installed on the city system if the city cannot provide them. But when these boxes are installed they become a part of the city system and should be serviced by no one but the Fire Alarm Bureau.

Under no condition should you allow a concern to have a box inside a building. The box should be mounted on a pole or standard outside the building.

When boxes are once placed they should not be removed later on as people get a location fixed in their minds and in case of fire run to the place they have been accustomed to seeing a box. If it is removed it will result in confusion.

In arranging a new system decide on a number system and stick to it. For example, if your city has wards or districts, have the first number of the box the same as the district number if possible. This will give a ready indication of the direction of the alarm, and will make it easier to memorize the box list. The second number may stand for the identity of the location, whether public, private, school house or street box, then the second number will give a ready reference to the type or nature of the alarm. The third and fourth numbers, should there be such, will act as the box number.

A lot of planning will be necessary for you to lay out your box locations in the best possible manner. Several things will have to be taken into consideration, including size of the city, distance from one block to another, special hazards, unsettled districts, etc., in order to get the best possible installation.

When receiving boxes from the factory it may be well to give them a test before placing them on the street. It should include: testing of the spring drive for proper driving power for all sixteen rounds, non-interference test, test for sticky doors and hook pulls, and a ground or break down test. Boxes are all carefully and thoroughly tested before they leave the factory, but sometimes they are damaged in transit.

If possible, get a liberal supply of spare boxes and hold them for emergency cases.

It is necessary to have a back board for all boxes that are placed on wooden poles and these can be obtained from a mill in your own city. They may be ordered through the manufacturers of your apparatus, but it is not customary to get them this way.

If you already have boxes for your installation it will be to your advantage to get the new type doors and install them as the extra cost will not be a great deal and the old doors will be taken back by the company that supplies your new doors.

In purchasing boxes get the best, do not consider the cost of the box in this case, as reliability is worth any extra cost incurred.

Batteries

The subject of batteries is important. The size of the battery racks is dependent on the “amount of battery” it is to carry. We will consider the batteries first.

The batteries used for fire alarm work are, as explained before, of two volts and arranged to be discharged at one tenth of an ampere. There are several reasons why a cell of this type is used, and we must take into consideration the size of the battery when figuring the number required.

A chart is made of the proposed circuits. The gauge and length of the wire being known, it is an easy matter to figure the resistance of the circuits. Beside the resistance of the circuit wiring itself, we must figure in the resistance of all the apparatus that will be cut into the circuit when the whole installation is complete. This will include the resistance of the magnets, of the repeater, gongs, relays, time stamps and registers on the main line; indicators, protectors, and all other auxiliary apparatus in the main line circuits, including the resistance of three or four boxes in order that the line will be able to function should the doors of the boxes be left open.

In order that you may be able to figure up the necessary battery that will be required in your particular system, a test example is given below:

Example: A circuit with the following resistance is to be supplied with battery sufficient to keep it at one tenth of an ampere. The resistance includes: 12 ohms of line wire, 100 ohms for four open boxes, 40 ohms for two six-inch gongs on the main line, 23 ohms for one indicator, 34 ohms for the repeater magnets, 30 ohms for a register, and 100 ohms for the resistances in the storage battery switchboard. The sum of this resistance is 339 ohms for the entire circuit. According to ohms law the pressure required to force a given current through a given resistance is the product of the current times the resistance. In other words:

Volts = Current x Resistance, or Volts = Amperes x Ohms. We know that we are to have impressed on the line at all times a current of one tenth of an ampere and we desire to find out what voltage will give us this result with a resistance of 339 ohms. Using the above formula we find:

Volts = .1 x 339 = 33.9 volts.

We would therefore need 40 volts of battery to keep the line at one tenth of an ampere. This formula may be used for any calculation where the current and resistance are known.

Where the voltage and current are known the following formula is used.

Resistance = Pressure Current, or Ohms =Volts / Amperes

In the above case the resistance would be as follows for the given value of voltage and amperage.

339 ohms = 40 volts / .1 ampere.

To find the amperage where the voltage and resistance is given, use the following formula:

Amperes = volts / ohms = 40 / 339 = .1 ampere

By the use of the formulas and the further use of resistance tables it is possible to get the proper voltage necessary to carry your circuits.

After the necessary battery is decided upon, you can then judge what size rack you will need. It will be well to comunicate with the makers of racks and give them the amount of battery you have and they can then tell you the size of the rack.

When getting a battery rack do not order one with just the bare amount of space on it to accommodate the battery already required as you will no doubt expand your system and will need additional space for more cells as time goes on.

When figuring battery for an installation, arrange to get some additional cells to take care of breakage and for building up new units, as will be necessary from time to time.

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