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lettering on such plates shall be painted with a paint of a color different from that used on the body of the plate, so that the letters will be prominent and distinct.

II. In case it may be desired, for architectural or other reasons, to vary from these requirements in the shape of construction of the brackets or railings, such changes may be submitted to the Fire Commissioner, but shall not be made until his approval has been obtained.

12. Windows. All windows opening on fire escapes to be approved self-closing, and to have metal frames and sashes glazed with wire glass.

CHAPTER XV.

Roofs Tanks and Tank Supports

Uses of Roof Tanks. In all tall buildings water is required for house use, for fire extinguishing, and sometimes for manufacturing purposes. All this water is generally pumped into one or more roof tanks, whence it descends through pipes in the various parts of the building.

Three kinds of tanks are generally used:

I. 1. House Tanks. These supply water for drinking, wash basins, water closets, boilers, as well as for cleaning purposes. House tanks are usually made of wood. All house tanks containing over five hundred gallons must rest on steel beams. In smaller buildings the house tank also supplies all water for fire extinguishing purposes.

The Fire Underwriters reduce the fire insurance rate on those buildings equipped with special water tanks and with a system of fire extinguishing pipes, forming what is known. as a sprinkler system. The sprinkler system is now compulsory, being required by law in all buildings of a certain height and with a certain number of people working above the second floor. The tanks used for the sprinkler system are known as gravity and pressure tanks.

2. Gravity tanks are made of wood, just like the house tanks, but are set upon a steel framing at a considerable height above the main roof, usually between fifteen and thirty-five feet. This height creates a certain required pressure in the sprinkler pipes.

3. Pressure tanks are used in addition with all sprinkler systems. These are iron tanks filled up two-thirds with water maintained under a constant pressure of about seventyfive pounds per square inch or more, by means of an air compressor. Pressure tanks rest on steel beams only two to three feet above the main roof and are enclosed in heated pent houses to prevent freezing.

In a twelve-story building on a lot 50x100 feet there were two pressure tanks, each containing 6600 gallons when filled up two-thirds. Then there was a 10,000-gallon gravity tank and a 6000-gallon house tank. As in all sprinkler systems, the house tank was connected with the sprinkler pipes and its contents could be used in case of fire if necessary.

LOCATION. No tank should be placed over a stair well, as it may interfere with the work of firemen in case of fire. It is a convenient arrangement in tall buildings to have the pressure tanks about two or three feet above the main roof and enclosed in a fireproof pent house, while on top of this pent house, both the house tank and the gravity tank may be placed.

Following are a few points requiring careful consideration in tank work:

I.

Elevation of Beams. Changes in the elevation of the tank-supporting beams, contrary to approved plans, are of common occurrence. This is sometimes done by causing each steel beam under the tank to be raised upon struts or posts which may not be sufficiently braced in between to insure rigidity.

2. Size of Beams. Changes in the size of beams supporting the tanks are also a common and risky operation. This is sometimes done by mistake, and where lighter sizes are used there should be no excuse for such an error.

3. Capacity of Tanks. This is often varied without modifying the sizes of the steel beams accordingly. To avoid unsafe conditions which may arise in this manner, a convenient table is given in Part Three for the capacity of cylindrical tanks of usual diameters. The capacity of square or other tanks may be easily figured into cubic feet.

The weight of a cubic foot of water is about 62.5 pounds and one cubic foot contains 7.48 gallons.

4. Bolting. In all tank towers bolting must receive special consideration. The various members and gusset plates will seldom match, and reaming holes into elongated slots or drilling new holes in between old ones is very usual. This may often render a gusset plate useless, unless the same is reinforced. Where holes have been elongated more than the diameter of the bolt shank and where any part of the hole is visible after the bolt is in place, washers should be used to cover up such holes, in order to keep away rain water and also to hold the parts rigidly together through friction.

Connections near the top of the framing are likely to contain bolts of smaller diameter than required. Very often five-eighth inch bolts are used instead of three-quarter inch bolts where holes did not match. This is partly due to the difficulty of operating a reamer or a drill high up in the air. It is, however, bad practice and should not be allowed.

5. Wind Bracing. All exposed roof tanks are regular targets for swift winds and storms. It is therefore essential to secure rigidity in all tank towers. This is done partly by. having plenty of tight bolts in all gusset plate connections and partly by using sway or X braces and tie rods. All X braces should be bolted at the middle where they cross each other, and should be well connected at each end. All tie rods used in between steel beams should be made tight, and where the beams are not too far, double nuts may be used at each end of each tie rod, to make the ties to act both in tension and compression.

6. Anchorage. This part of the tank tower takes the full effect of wind pressure and must be carefully inspected. Whenever anchors must go through brick or other walls, the inspector should see that this is properly done.

7. Saddles. Pressure tanks are generally cylindrical in shape and rest upon cast iron or steel saddles. These sadIdles keep the tank from rolling and should be bolted to the iron beams.

Where the tank supporting beams are not set exactly level on top, each beam should be made to get its share of the tank load by providing tight wedges or shims between the tank and the beam. Whenever possible this should be done before the tank is filled up with water.

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