Questions and Answers
NOTE—Readers are invited to send in questions, which will be answered in the order received. Names are omitted from questions unless otherwise specified
To the Editor:
Can you tell me what became of the company that manufactured the old Amoskeag steam fire engines? I am looking for some information on the capacity of the engines used at the time of the Chicago Fire of 1871. I note that engines were then classed first, second and third class. Do you know the pumping capacity of these classes at the time under consideration.
H. A. M.
Answer: Amoskeag steam fire engines were built by the Manchester Locomotive Works, Manchester, N. H. This company has been out of business for many years.
The Amoskeag first class engine had a discharge capacity of 900 gallons per minute; the second class engine had a discharge capacity of 600 gallons per minute.
No third class engines are listed in any of the early handbooks on fire engines so that the rating of the third class engine is not known.
These figures apply to the engines used at the time of the Chicago Fire, 1871.
Friction Heat Ignites Hose
To the Editor:
We have had quite a number of debates on whether the friction of water in fire hose will burn the rubber lining.
It is claimed that a small stream of water leaking through a hose clamp will burn the rubber lining. For that reason we have been taught to place the hose clamp about eighteen inches behind the coupling, so that if the lining is burnt, only a small piece at the end of the length need be cut off. M. R. B.
Answer: Although we know of no instance when hose lining was ignited by water, John S. Caldwell some years ago reported two cases of fire hose charring when water was flowing through it.
The first occurrence hapened during the operation of a motor pumping engine in the Boston Fire Department, resulting in the burning of a bole in the cotton jacket of the hose about the size of a half dollar at a point near the coupling, where attached to the pump. Shortly following this, he had the opportunity of duplicating this condition, and subsequently conducted two tests under similar conditions with practically the same results.
The following is the condition under which the burning occurred. A single line of 2 1/2-inch double jacket cotton rubber-lined hose, to which was attached a deluge set. with a 1 3/4-inch outlet, was connected to a 750-gallon automobile pumping engine, equipped with a rotary pump. The pump was operated so as to maintain 250 pounds water pressure on the discharge gage by throttling the gate on the pump, so that an opening of only 3/8 to 1/2-inch was obtained, and discharging only a comparatively small amount of water, from 250 gallons to 300 gallons per minute, at a very low pressure at the nozzle. The throttling of the discharge gate produced a stream of very high velocity, the direction of which was at an angle with the discharge outlet, due to the valve opening being at the side. This high velocity jet, so to speak, impinging against the side of the hose near the coupling where connected to the pump discharge outlet, caused a slight deflection or distortion of the hose at the point of impact, and resulted in excessive vibration or fluttering of the hose, together with slight indentation or kink on the under side, due to an insufficient volume being discharged to properly stiffen the hose line. After a period of two to three minutes, the hose commenced to get perceptibly warm on the under side near the coupling. In about two minutes more the cotton jacket became so warm that the hand could not be retained against it. The next indication was the distinct odor of hot rubber, followed by smoking and gradually by a discoloration of the outer jacket as the cotton fibres were carbonized; the fibres then commenced to fray and part, and as the outer jacket let go, it was observed that the inner jacket was carbonized in the same manner, followed quickly by the bursting of the hose at this point, due to the lack of support for the rubber lining. The total time consumed in bringing about this condition was approximately fifteen minutes.
From the above information it is quite evident that fire can be caused in the hose jacket as a result of flow of water within the hose.
Buoyancy of Metal
To the Editor:
A standpipe three inches in diameter and 20 feet high has a consistent water pressure of 50 pounds. If a 50-pound weight, having sufficient vent to allow the water to go by, is placed in the pipe, would this weight stop at a certain position on the way down the pipe where the weight would balance the pressure of the water?
If the water pressure fluctuated, would the weight fluctuate accordingly, but come to a dead stop at a position where it would balance the pressure?
If the pipe should suddenly he moved, would not the weight remain in its position in relation to the water pressure ? T. K.
Answer: The weight in the standpipe would drop to the bottom. A body immersed in fluid is buoyed up by a force equal to the weight of the liquid displaced.
Assuming that the weight you refer to is of metal, iron or lead, then the amount of liquid displaced by it will weigh less than the weight; hence, the buoyant force will be less than the weight of the metal, and the metal will fall to the bottom of the standpipe.
As water is practically incompressible, its density does not change materially, even at great depths. Therefore the weight would settle to the bottom even if the standpipe were a mile in height.
To the Editor:
I would appreciate the answers tothe following questions:
Question 1: In determining the back pressure on a nozzle, the formula 1.5 x d2 x p is used. Will you please inform me how this formula is derived?
Question 2: Is there any difference in the back pressure of a short and a long nozzle? If so, what?
Question 3: Can this formula be used on all size nozzles for Fire Department use? C. L.
Answer 1: The formula for determining nozzle reaction is classed as an empirical one. It was developed to fit experimental results and has no scientific background.
Answer 2: There should be no appreciable difference between reaction of short and long nozzles, it nozzle diameters and pressures are the same.
Answer 3: This formula can be employed for all sizes of nozzles.
Carbon Dioxide and Carbon Monoxide
To the Editor:
I am under the belief that carbon monoxide is composed of one part carbon and one part oxygen. Oxygen is necessary for combustion, yet this gas, which has such a low oxygen rate, is highly combustible. On the other hand, carbon dioxide has one part carbon and two parts oxygen, yet this gas will extinguish fire. I should like to know why the carbon monoxide, with its low oxygen rate, is more combustible than carbon dioxide, which has a higher rate of oxygen. C. L.
Answer: When carbon burns, it forms a chemical combination with oxygen. If complete combustion is accomplished, the product of combustion is carbon dioxide. In other words, each part of carbon takes into chemical combination with it two parts of oxygen.
If incomplete combustion is produced, such as where the carbon burns in the presence of insufficient air, carbon monoxide is formed. Carbon monoxide represents a gas in which not all available carbon is united with oxygen to form a complete, stable, combination, carbon dioxide gas. Carbon dioxide is similar in make-up as water, which is composed of two parts of hydrogen and one part of oxygen. Free hydrogen will burn in the presence of oxygen with explosive violence, but the two gases when combined chemically form water, which, like carbon dioxide, is a fire extinguishing agent.