Boiler Accessories Boiler Explosions

Mismanagement. The pressure in a steam boiler may rise above that at which the safety-valve has been set to operate, because of corrosion or overloading of the valve. Stop-valves are sometimes placed between the boiler and the safety-valve; but this practice should be condemned, as it is possible that the stop-valve may be closed when the fireman thinks the safety-valve is open to the boiler pressure. If the size or lift of the safety-valve is too small, steam may be generated faster than it can escape, in which case the pressure will rise in spite of the safety-valve. It has been claimed that the blowingoff of the safety-valve when the boiler is under excessive pressure may be the cause of starting an explosion; but the reason why this should he so does not seem to be especially clear, and it seems to be improbable if the opening of the safety-valve is sufficient to cause a reduction in pressure. Safety-valves have sometimes been loaded down temporarily to prevent leakage at working pressure; hut such a practice is little short of criminal. If a safety-valve leaks, it should be reground, but under no circumstances should the weight on the lever be altered.

It is a common idea that when the furnace plates become very hot, perhaps heated to redness, due to a lack of water, and the feed is turned on, a violent explosion is sure to follow. Experiments show that when a piece of wrought iron is heated to redness and plunged into a weight of water three or four times greater than that of the iron, a comparatively small quantity of steam is disengaged. There is no reason to believe that this quantity would be greater if the iron were in the form of a boiler than in the form of a plate. If a small quantity of water were admitted to hot plates, the danger would be greater; and while a boiler under this condition might explode, the comparatively small quantity of water in it would make the resulting danger much less than if the boiler were under working conditions.

The following experiments illustrate the action of cold water on hot plates. A boiler 25 feet long and 6 feet in diameter was heated red hot and the feed turned on. No explosion occurred ; but the sudden contraction of the overheated plates caused the water to pour out in streams at every seam and rivet-hole as far as the fire-mark extended.

In another instance, the water was almost entirely drawn off while the fires were burning briskly. When the remaining water had been converted into steam and all the fusible plugs melted out, water at the rate of 28 gallons per minute in a series of fine jets was played on the hot plates. Such treatment may ruin a boiler for further service, though the boiler may not explode.

That a tough paper or cloth is easily torn when once a tear is started, is a well-known fact. Similarly a boiler-plate may be niptured at slight pressure if a fracture has been started.

The position of the fracture or hole has a great influence on the results. In case a large rent occurs at the top of a cylindrical boiler, the steam and hot water may blow out of the hole; and the boiler, if strongly enough seated to stand the reaction, will remain on its seat.

The damage to the boiler would be slight. But suppose the same rent were situated on the under side of the boiler near the ground or floor; the effect would be very different, the reaction of the escaping steam would probably blow the whole boiler through the roof.

Investigation. When an explosion occurs, it should be investigated, not only to fix the responsibility where it belongs, but also to provide for and take means to prevent future disasters. It has been customary to attribute all explosions to low water, since it is an easy way to throw the responsibility from the makers or owners upon the fireman, who, even if living, cannot defend himself. In the investigation of an explosion, the weights, shapes, positions, and directions of the scattered pieces should be noted, so that their original places may be known. The original size and shape of .the boiler and of the fittings should be known as accurately as possible. The primary rent may be discovered from comparison and from deductions of the directions taken by the heavier pieces. Light pieces will generally take the direction of the escaping steam, while the heavy parts take an opposite direction, that of the reaction. A careful examination of the pieces, noting the age of fractures, thickness of plates, amount of corrosion, condition of plates, etc., will generally show the cause. A test of the plates will in many cases show any softening or yielding to the pressure and excessive thinness caused by bulging.

Prevention. The means taken to prevent boiler explosions from most of the above-mentioned causes, have already been given. It is of primary importance that at the start only a well-designed and well-made boiler should be used. The matter of type is not of so much importance; but it is well to use a sectional boiler in large cities or in buildings where many people are employed. There are many methods, some of which have been discussed, that are taken to prevent deterioration by corrosion, fracture, etc. Proper setting is of great importance in this matter. Mishaps from mismanagement may be greatly lessened by the employment of licensed attendants. A boiler should never be in the hands of a man who is not thoroughly competent to run it. The most effective method to prevent explosions is the law of the State, compelling regular, thorough inspection and licensed firemen. The inspection by the Boiler Insurance companies is also an efficient method.

During a period of eleven and one-half years, 70,000 boilers were inspected by Boiler Insurance companies. It was estimated that there were 140,000 in use during that time. Of the inspected boilers, there were 23 explosions and 50 collapses, resulting in 27 deaths from explosions, and 28 deaths from collapses. The explosion rate was 1 in 11,000; and the death rate, 1 in 14,600. The uninsured boilers did not make so good, a showing, the death rate being 1 in 5,000 boilers, or about 3 times as high as among the insured boilers.