From year to year, non-movable assets become higher and occupy larger areas. Nowadays, for this reason, the common fire protection measures (a fire extinguisher and even a fire hydrant) are extremely ineffective. A fire alarm system is a set of interconnected devices aiming to detect fire and settle it in the early stages of development. The system is often integrated with the fire alarm, warning system, and evacuation control. The fire alarm system should be in every commercial, industrial, and office space. Even the application of modern technology does not guarantee a complete safety from fire. However, in order to minimize its impact, an early detection and warning about fire is very important. The purpose of the fire protection system is to protect people and property from the effects of fire hazards and limit its consequences. The paper will discuss advantages and disadvantages of various systems used in fire prevention.
The main fire extinguishing systems used today are gas, aerosol, foam, powder, and water. From year to year, they are constantly improved in order to minimize the impact of fire. Water systems are the ones of the most widespread systems. Nowadays, a sprinkler system is very popular, since it is considered to be the most effective one. It has this name because of the spray devices-sprinklers. “The basic principle of the sprinkler system is that flame is removed with the help of water spraying under high pressure”. The main element of the system is a sprinkler. It is a spray head, which is integrated into the fire-extinguishing system. It is set mostly on the ceiling. The system monitors a situation inside the building through installed sensors that determine the temperatures and smoke.
Fire sprinkler systems consist of sprinklers mounted in a pipeline, where water or air is under pressure. The principle of operation of sprinkler systems is based on a pressure drop in the system in case of fire. In such case, the ambient temperature increases, and when it reaches a certain temperature, a sensing element in the sprinkler is destroyed. Inside the temperature sensing element, there is a capsule with alcohol liquid depending on the color of the liquid, the temperature sensing element may have the failure temperature from 57 ° C to 182 ° C. After the destruction of the temperature sensor, water or water-foam solution begins to escape outside and pressure in the system drops. Then, the control of liquid operates; and the pump starts in a pump station. For fire sprinkler systems, rooms for the pumping station with pumps and supplying water are designed separately. There are special requirements for the construction and design of stations. In addition, the system should have two pumps, i.e. primary and backup.
If there is a threat of fire, these are sensors detecting smoke or increase of the temperature above normal. They transmit a signal to the control unit. The latter, in turn, activates the sprinkler system, which with the help of sprayed water liquidate fire. The main disadvantage of the system is a sufficiently large inertia of operation of sprayers. The fire suppression system can be easily installed at home. Obviously, it is an advantage. As soon as there is fire in the room, the system not only notifies the owners, but also begins active defensive actions allowing saving property and housing from fire. Also, a quite important advantage of the sprinkler system is the use of water as a fire-extinguishing medium. It has low rates of cost and in abundance almost everywhere. Another positive factor in favor of the use of water as a means of fire suppression is its non-toxicity. Taking into account that the sprinkler system is used for ordinary drinking water, the spray liquid will not harm the human body.
There are water filled sprinkler systems for the rooms where the temperature is 5 °C and above. Air systems for unheated rooms are with the temperature being below 5 °C. The basis of the sprinkler system is a network of pipes with sprinklers divided into sections (the number of sprinklers installed). The section of the sprinkler system can protect one or more rooms. Each section is provided with a separate control unit.
In recent years, domestic sprinkler systems have gone through a lot of improvements. Nowadays, schemes of sprinkler fire suppression systems are designed in a way that they can work as efficiently as possible if necessary. In the modern system, a plastic pipe is used, which without the loss of quality and efficiency helps reduce installation costs and significantly simplifies the process. The modern sprinkler system activates only those sprayers which are located very close to the hearth of fire. Therefore, the effect of water only occurs in the area of ignition. Thus, the negative influence of liquid is minimized. One should always remember that the damage from water is many times smaller than the effect of fire arising due to the lack of elimination of fire.
Smoke Management Systems
“A smoke removal system is a complex of technical means to enforce the removal of smoke from the premises”. It is an important constituent element of the fire protection of the facility. Smoke extraction systems are necessary in case of high concentrations of smoke during fire. The smoke removal system is a special controlled automatically or manually technical system of supply and exhaust ventilation. An objective of the smoke exhaust system is to provide conditions for the evacuation of people in case of fire.
Smoke extraction systems are usually expensive systems, a suitable structure, and specifications that require a special design. The system is designed to remove the products of combustion (smoke) and limit its spread in order to ensure the evacuation of people from the building in the initial stage of fire. “Smoke removal is best for suited for large volume spaces such as atriums, indoor stadiums, airport terminals and indoor malls”. Systems are typically performed with automatic control (with complex security systems, an automatic fire alarm system, and automatic fire extinguishing) or semi-automatic control (launching is carried out by a personnel on duty or tenants of the building after receiving the information about the fire).
In case of fire, in the propagation of smoke in the building, the smoke removal system opens the windows and hatches designed to smoke exhaust. As a result, smoke and combustion products, as well as excess heat leave the building and the ways of the evacuation of people remain free of smoke. To achieve the thermal motion of smoke in the upper part of the building, where usually, windows and hatches are placed, it is necessary to open simultaneously windows in the bottom of the construction. It is extremely important, as it provides the quick purification of areas with smoke. Although, smoke exhaust systems have been designed primarily as fire safety systems, they can be used for natural ventilation. High technology of control units allows connecting various automatic sensors to them, both fire and weather. The structure of smoke removal systems include:
- Smoke dampers are set in the protected areas. They provide acceptance of flue gases and their direction in smoke mines. They have a magnetic drive.
- Fans are designed to create a vacuum and exhaust of flue gases from a protected area.
- Ventilation ducts are made for the transportation of flue gases from a protected area outside. They are made of non-combustible materials.
- Fans of air overpressure. They create overpressure in elevator shafts, stairwells, and air locks to avoid smoke blanketing.
- Fire dampers are placed in the systems of exhaust and general ventilation to limit the spread of dangerous fire factors.
Gaseous Fire Suppression
Recently, gaseous fire suppression systems have become increasingly popular. They belong to the most economical ones. They reduce the amount of oxygen in the room by means of carbon dioxide or inert gas. Without causing any harm to the objects in the protected area, this kind of fire suppression can extinguish ignition of flammable materials, liquids, and gases. These systems are recommended to use in rooms with a lot of electronic equipment, electrical equipment, as well as the research and scientific laboratories.
“Gas fire suppression systems are cylinders of various sizes with a triggering device for the production and storage of fire-extinguishing gas mixtures”. Substance is used that during localization of flame is in a gaseous state. Localization of ignition is carried out by filling the room with a fire-extinguishing gas mixture. The operating principle of the system is based on a significant reduction of the concentration of oxygen with the help of incombustible gas. The launch of gas fire extinguishing installations is realized by electric, pneumatic, pneumoelectric, mechanical, or electromechanical means. According to the manner of extinguishing, gaseous fire suppression systems are divided into systems of the local fire area, local fire volume, and total flooding.
In total flooding, the fire extinguishing agent is fed into the room with the help of sprayers. There should not be more than six sprayers on one branch. Systems of total flooding are applied to protect premises that have an area of constantly open apertures not more than 10% of the total area of the enclosing structures. In systems of total flooding, there are the following extinguishing agents: Freon 125 (С2F5Н), Freon 227ea (С3F7Н), Freon 114B2 (C2F4Br2), and Carbon dioxide (CO2).
To extinguish the ignition of equipment, as well as in cases where the use of total flooding systems is economically unreasonable or technically impossible, local firefighting is applied.
An advantage of using gas fire extinguishing systems is that they are able to extinguish fire at any point of the volume of the protected space. At the same time, these systems do not cause damage to the premises and equipment. Gases, which are used in fire fighting are environmentally friendly and do not harm people and the environment. Gas is not electrically conductive. Therefore, it can be used to extinguish the high-voltage equipment. Unlike other systems, gas fire suppression systems do not freeze. They are not afraid of heat.
In the matter of evacuation and rescue of people, an important role is played by an automatic fire alarm system. “It has become necessary in many cases to connect building control systems, such as heating and ventilation systems to the fire alarm system”. The automatic fire alarm system is required for the detection of the source of fire and subsequent notification about it. At the facilities, there are fire sensors, which in the case of smoke will work and give a signal. The fire alarm system can be: analogue, address, and threshold. In a threshold fire alarm system, a detector has an operation threshold. For example, fire detectors are thermal, and, at a certain temperature, they give the signal to the main control panel of the fire alarm. Another feature of the threshold system is the so-called radial topology of constructing of alarm loops. There are special cables in different directions from a control panel of the fire alarm system. Each cable can be connected to about 20-30 smoke detectors. The smoke detector is activated; and the control panel displays the number of the cable that is connected to this detector. The main drawback of this alarm system is its inability to check the efficiency of sensors, as well as the low self-descriptiveness of received signals. In addition, another drawback is a later detection of fire.
The address fire alarm system is different from the threshold system by the algorithm, by which the sensor communicates with the control panel. In the threshold system, the control panel expects to receive a signal from a flame sensor about a state change. Meanwhile in the address system, the control panel just sends connection requests of smoke detectors. Identification of their status is a main purpose of the request. This algorithm enables to obtain the complete information about efficiency of devices. The smoke detector is a part of the constant awareness. However, the fire alarm sensor is triggered not instantaneously. As a consequence, a significant drawback of the system is later fire detection.
In the automatic fire alarm system, the analog technology is the best option. This alarm and fire detectors have several advantages. The main advantage is that the control panel and not the sensors make a decision on the state of an object. This automatic system is more efficient than its analogues.
Of the variety of fire-technical equipment, pumps are the most important and complicated ones. In firefighting vehicles, there are various pumps operating according to different principles. Primarily, pumps provide a supply of water to extinguish fires. Pumps are used in many auxiliary systems such as vacuum. The widespread use of pumps is caused not only to their device, but the performance and features of their operation modes. It provides an effective use of pumps for fighting fires. Currently, there are various types of pumps used in the fire engines. They provide a supply of extinguishing agents, the operation of vacuum systems and operation of hydraulic control systems. Pumps may be centrifugal, jet and gear.
“The most common fire pump in use is the electric-driven, horizontal shaft, single stage, centrifugal pump”. The firefighter centrifugal pump for fire-fighting vehicles is a pump unit consisting of a pump, discharge manifold, valves and regulating purposes, a vacuum filling system, a system of feeding, and dosing frother. Centrifugal pumps are extremely widespread. It is due to the fact that these pumps have a number of advantages: uniformity, supply without pulsation, as well as a simple operation of the pump. By overlapping a fire barrel, pressure does not raise excessively in the water supply system. It ensures a reliable operation of the pumping unit. For fire-fighting vehicles, it is important that centrifugal pumps do not require the sophisticated drive from the engine. Their dimensions and weight are relatively small.
Centrifugal pumps have a number of drawbacks. They do not suck fluid and work only after pre-filling the suction line and pump by water. This shortcoming is compensated by devices that allow filling the induction tract and the pump housing from the tanks. In addition, on the fire engines, there are auxiliary pumps to fill the cavity of the suction hose and the pump housing with water. For this purpose, gas-jet, rotary and other pumps are used. Auxiliary pumps operate not for a long time. The installation of these pumps complicates the construction of the pumping unit. It requires the device of the additional drive for their work. The pump operation is accompanied by the action of axial forces. It increases the load on the bearings and reduces their longevity. On fire engines, single-stage centrifugal cantilevered pumps are used. The maximum geometric suction height is 7 m.
Aerosol Fire Suppression Systems
“Aerosol fire suppression systems are an emerging technology that offers an alternative to clean agent and specialized water-based fire protection systems”. The aerosol fire suppression system is a way to extinguish fire using products formed during combustion of aerosol mixture. These combustion products have powerful capabilities on the localization of seats of fire. Aerosol systems reduce the spread of fire in the territory due to the direct action on the ignition source.
Regardless of manufacturers, similar aerosols operate on the same principle. Aerosol mixture contains certain chemical substances. When they burn, there is a hot stream of gases and solids. This hot jet has extinguishing abilities. Quenching starts due to stoppage of chain reactions in the midst of fire. Aerosol systems effectively suppress the spread of fire, localize and eliminate the source of fire. These systems are extinguishing aerosol generators. This device releases some spray with extinguishing characteristics and distributes it throughout the room with fire. The generator contains the aerosol forming substances. Their special structure can burn without the inflow of air. In a process of its combustion, there is aerosol. Aerosol formed during combustion has a quenching effect. The mechanism of its action is the deceleration of chemical reactions that promote burning. When a room is filled with aerosol in the desired concentration, the amount of heat released during combustion is drastically reduced. Therefore, the temperature decreases, and fire is localized. It is important that after the generator is disconnected, the aerosol concentration is kept up to fifteen minutes. So, re-ignition is impossible. During spraying of the aerosol composition from the generator, its solid particles form a film. The appearance of the film prevents the access of oxygen to fire. When the fire is extinguished, the resulting film can be removed. It is removed without damaging the surface by conventional detergents. The fire extinguishing aerosol generator can be activated manually or automatically from the inclusion of the fire alarm. The generators are used for electrical appliances, inflammable solids and liquids.
Some people sometimes underestimate the meaning of fire protection, as they mistakenly believe that fires are rare. However, the fire safety system at apartments, houses, offices, and factories is extremely important. Fire safety, in particular, the design of the fire alarm system and fire extinguishing, is a key to peace, the protection of property from fire, as well as a guarantee of safety. Fire-prevention safety of buildings and structures is a condition without which any enterprise, administrative or public institution cannot exist. The main causes of fires are breaking the rules of fire safety. Observing fire regulations is a key of well-being and safety. The paper has discussed advantages and disadvantages of aerosol fire suppression systems, fire alarms, fire pumps, gaseous fire suppression systems, sprinkler systems, and smoke management systems.