One of the principle safety concerns for any premise where individuals live or work, is protection against the emergence of an open fire source. All factories, office buildings, and other production facilities therefore have access to a small coiled fire hose as a first line of defense in an emergency situation. If a situation becomes dire, a fire truck, equipped with fire hoses, is deployed to mitigate the risk of injury and extinguish the fire. As the fire hose is an indispensable attribute of a fire truck, and is often deemed one of the most important elements, the fabrication and quality of the hose is of the upmost importance.
By Jurij Artiukhov, General Manager, PipeTime, LLC
A fire hose is a flexible pipeline system that is used to transport water, or other extinguishing agent, from a water source to a fire site. Any emergency rescue unit aimed at extinguishing a fire is equipped with this technical application. Most countries in the world regulate the manufacturing of a fire hose by state standards, however, technical progress is often ahead of regulatory documentation.
Manufacturing Process
In general, a fire hose is made through an extrusion process. Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section to make the product in question.
The initial stage of fire hose production is the preparation of rubber for the manufacture of an internal sealing chamber (layer). At this stage, various additives can be added to make the hose resistant to aggressive elements that make up fire-extinguishing mixtures, increase its strength, and make it more resistance to temperature conditions.
The rubber frame of the hose is then made on an extruder, which uses a special nozzle that allows the operator to adjust the frame to the desired size (diameter). As the rubber hose exits from the extruder it is important to carry out a measuring control of the resulting hose diameter. Typically, a step gauge is used for this control, to check the inner diameter of the fire hose. Once the hose is extruded, it is laid on a braiding device that forms braiding and rubber layers between each other.
Alternatively, a fire hose can be vulcanized. Vulcanization refers to a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to include the hardening of other rubbers via various means.
For this process, the hose is rolled out, measured using a specific tape measure, and selected by length.
Hose Testing
The tightness of the hose is checked by raising the pressure by 1.25 bar from the working pressure. The test results are considered positive if the hose withstands the given pressure, and there are no drops of moisture on the connecting elements. There are other test criteria, but these are the most paramount.
Types of Fire Hoses
Fire hoses typically fall into two categories: suction and discharge hoses, and discharge hoses.
Suction and discharge hoses
In areas where fire extinguishing has an absence of a stationary point of water intake, such as a sewer network or a hydrant, it is necessary to find a source of fluid. If, for example there is a forest fire, the nearest source of water may be a lake or a river. These types of situation require the use of a suction hose. As the creation of a vacuum is required to draw water into the hose, the structure of the fire hose itself must be capable of withstanding the pressure necessary to draw in, and then eject, the water.
The structure of a suction and discharge fire hose is most often a rubber frame reinforced with fiber and steel wire as a power cord. As a rule, such hoses have diameters that range from 50mm to 200mm and are limited to 4m in length. Since fire extinguishing requires efficiency, and a 200mm hose meter already weighs about 7kg, the 4m length limitation was introduced so that fire brigades could deliver the hose to the place of water intake without needing additional manpower or equipment.
The hose’s operating temperature, depending on the climatic version, varies from -50˚C to 90˚C and the working vacuum pressure is never less than 0.8 bar. To enable the installation of connections (compression with clamps), both ends of the pressure-suction hose are soft areas without steel wire; roughly 15 cm long.
Discharge hoses
Discharge, or pressure fire hoses are typically used when a stationary point of water intake is available, such as a hydrant. These hoses are considered the fire extinguishing tool itself, as they supply water, or other chemical means, for fire extinguishing to the fire source.
In the middle of the 20th century, pressure fire hoses of were made of flax, which made them inconvenient in operation. They had to be dried every time they were used, they were not repairable, and would become soaked in water during use, making them very heavy. Modern production of pressure fire hoses uses synthetic thread, which eliminates the absorption of water. It is also a durable, lightweight, and comfortable material.
Depending on the characteristics of the manufacturer’s plant and its geographical location, fire pressure hoses are manufactured with diameters that range from 25mm to 150mm; occasionally 200mm hoses are fabricated. The working pressure of these hoses range from 10 to 30 bar and the pressure is directly dependent on the diameter of the hose; the larger the diameter, the lower the operating pressure.
It is interesting to note that fire hoses are commonly used in applications besides extinguishing fires. They can often be seen used as a flexible pipeline through which the city’s utilities pump out wastewater from the hatch, used as a temporary bypass in case of a burst of heating system, and used for watering plots, fields, and gardens.
The length of the hose, as a rule, is regulated by 20m, less often 30m. However, the extrusion method allows cutting up to 200m. The length of the hose is typically dependent on the nature of the hose application. If the hose is to be used in an office building with fire equipment, then, objectively, the length of 20m is ideal both for placement in a box and for manual operation in case of fire.
Large lengths – up to 200m – make it possible to simplify forest fire extinguishing by an order of magnitude, when the water supply point can be located at a distance from the fire and it is impractical and extremely labor-intensive to build a flexible pipeline line in 20m segments. Long hoses can also be beneficial as a large number of connecting elements increases the risk of water leakage, which will affect the volume of water supplied. Climatic performance also depends on the geography of application; the operating temperature of pressure fire hoses ranges from -50˚C to + 80˚C.
Types of discharge hose
Fire pressure hoses, themselves, can be further divided into three subtypes:
- Type 1: A hose with an inner waterproofing coating, but without an outer coating, that is, the outer layer is a synthetic thread. These hoses are mainly used in stationary fire extinguishing systems. In professional jargon, they are called ‘standard’ type hoses. These hoses must also be rolled from time to time (usually at least once a year) in order to prevent; creases, the process of decay, and drying out in places of folds.
- Type 2: A hose with inner waterproofing coating and impregnated inner frame (latex hoses). This type of hose is excellent for wear resistance, working pressure, resistance to various aggressive liquids.
- Type 3: A hose with double-sided polymer coating. This type of hose is also ideal for wear resistance, working pressure, resistance to various aggressive liquids.
It is customary to apply markings on hoses to identify each type so that the appropriate hose is chosen for the situation at hand.
As the process of rolling out a hose is quite manually laborious, special machines have been developed to speed up the process of unwinding a fire hose for extinguishing a fire on an open surface.
Other forms of categorization
Although the classifications listed above are the most standard way to subdivide the hose types, there are alternate manners to categories the hoses. In Russia, for example, pressure hoses are often divided into types according to their resistance to certain external influences:
- Normal one.
- Heat-resistant (resistance to high temperatures and, therefore, the possibility of using near fire and location on a heated surface).
- Oil-resistant (if it is planned to pump liquids or emulsions containing petroleum products along the hoses, as well as use at the facilities of the oil and chemical industry).
- Wear-resistant (for work in conditions of constant drag on various rough surfaces).
Fire Hose Connectors
When a hose is connected to the place of water intake; a pump, a stationary pipeline, a hydrant, or if the hoses are connected to each other, it is mandatory to use specific types of connections. For example, a camlock, or in Russia, a Bogdanov connection is often used. The most common type of fire connection in the world, however, is the STORZ type.
STORZ is a hose tip with two (or three) claws, which, when attached to each other, are inserted into special grooves and rotated until they are fully connected. Connecting hoses to this type of tip can be carried out manually. If the connections are being used to build a flexible pipeline line that is several hundred meters long, the use a special tightening wrench becomes appropriate.
The STORZ hose tip has a wide range of adapters that allow it to be used on multiple standard size hoses. They can also vary in design: threaded ends, flange ends, and materials: stainless steel, brass, and aluminum.
Installation of connections on fire hoses is done in two ways: tightening the fitting at the end of the hose with a steel clamp, or winding steel wire along the entire length of the connection installed inside the hose. Wire winding is a more reliable method of fastening the connection; as the wire can be made of brass, if it is intended to use hoses in places where sparks are undesirable, and brass, as a material, provides intrinsic safety.
Final Thoughts
In the event of a burst or leak, as a result of high water pressures, fire hoses are repairable. To repair the hose, special tape clamps (to eliminate longitudinal tears) or corset clamps are used. This is, however, uncommon as significant amounts of time are dedicated to ensuring the quality and integrity of the hose. A thorough understanding of the manufacturing process and which hoses are suitable for which application are necessary to ensure the effectiveness of the hose and the safety of the operator. A correctly selected hose will warrant its trouble-free operation and reliability throughout the entire period of operation.
ABOUT THE AUTHOR
Jurij Artiukhov works as the General Manager at PipeTime, LLC. He previously worked as a Sales Manager for MTT Company and Project Manager for SOL SP Company. He holds a graduate degree from the University of Foreign Affairs, Economy and Law.