Fire extinguishing foams are a mixture of gas and liquid.
Fire extinguishing foams are a mixture of gas and liquid.
On gas – V-I, V-Ia, V-Ib, V-Ig; On the dust – B-II, B-Iia.
II – rooms in which flammable gases or flammable vapors are emitted in such quantities and have such properties that can form explosive mixtures with air under normal operating conditions (there is always an explosive concentration – loading and unloading of technological devices, storage or transfusion of flammable substances).
B-Ia and B-Iia – premises in which explosive mixtures are formed as a result of an accident or malfunction of devices, installations, and in normal conditions of operation of technological equipment explosive mixtures are not formed.
B-Ib – the premises are characterized by the same indicators as in B-Ia, but have the following features:
Combustible gases have a high lower explosive limit (15% or more and a pungent odor at maximum permissible concentrations); There may be a local explosive concentration; Combustible gases of flammable substances are in such quantities that do not create a general explosive concentration in the room, work with them is carried out without the use of open flames. These premises are non-explosive, provided that the work is performed in fume cupboards or under an umbrella).
B-Ig – outdoor installations that contain explosive vapors, gases and flammable substances (storage of flammable substances).
B-II – rooms in which dust is released, which turns into a suspended state, which is able to form explosive systems with air and other oxidants during normal short-term operation of technological devices and equipment.
According to PUE in fire-hazardous zones the closed electric equipment is used,
In explosion-hazardous areas and outdoor installations it is necessary to use explosion-proof electrical equipment manufactured in accordance with GOST 12.2. 020-76 "Electrical equipment is explosion-proof"…
Means and methods of fire extinguishing. A fire that has arisen can be eliminated by removing one of the three factors necessary for combustion: combustible substance, oxidizer, heat source.
There are two ways to put out fires: physical and chemical.
The physical methods of cessation of combustion include:
cooling of the combustion zone or combustible substances; dilution of reactants in the combustion zone with non-combustible substances; isolation of reactants from the combustion zone.
The chemical method of extinguishing a fire is chemical inhibition of the combustion reaction. The main means of extinguishing a fire (by means of which one or another method of cessation of combustion is carried out) are:
water (in the form of a jet or in a sprayed state); inert gases (carbon dioxide, nitrogen); chemical and air-mechanical foams; powder mixtures; tarpaulin and asbestos covers.
The choice of certain methods and means of extinguishing fires is determined in each case depending on the stage of development of the fire, the extent of fires, the peculiarities of combustion of substances and materials.
Water is the cheapest and most common extinguishing agent. This is due to:
high heat capacity (heat of vaporization 539 cal / g); high thermal stability (decomposes at temperatures above 1700 ° C); a significant increase in volume during vaporization (1 liter of water during evaporation forms more than 1700 liters of steam); cools the combustion zone.
Water is used in the form of powerful jets and as steam. A stream of water knocks out the flames and cools the surface at the same time. A jet 123helpme.me of water quenches solid flammable substances; rain and water dust – solid, fibrous bulk substances, as well as flammable and combustible liquids (alcohol, transformer oil, etc.). Water vapor is used to extinguish fires in rooms with a capacity of up to 500 m3 of small fires in open installations.
Industrial enterprises have external and internal fire water supply. The required water pressure is created by stationary fire pumps, which provide the supply of compact jets to a height of at least 10 m or mobile fire pumps and motor pumps that take water from hydrants. Internal fire water supply is equipped with fire hydrants, which are installed at a height of 1.35 m from the floor inside the premises at the exits, in the corridors, on the stairs. Each fire hydrant is equipped with a rubber hose and a fire barrel.
To extinguish fires inside buildings, in addition to fire hydrants, automatic sprinkler or drencher installations are installed. The sprinkler system of the water system is an extensive network of pipes under the ceiling with sprinkler heads (sprinklers), which are closed by fusible locks designed to operate at a temperature of 72, 93, 141, 182 ° C. The units have a control-signal valve, which passes water into the sprinkler network, while simultaneously giving an audible signal, controls the water pressure before and after the valve.
Drencher installations are equipped with spray heads which are constantly open. Water is fed into the drencher system manually or automatically when fire sensors are triggered, which open the group action valve.
Inert gases (carbon dioxide, nitrogen, argon, etc.) are especially useful when the use of water can cause an explosion or spread of combustion, or damage to equipment, facilities, valuables.
Carbon dioxide has two functions: cooling and insulating.
Carbon dioxide is a colorless and odorless gas. It is 1.5 times heavier than air; at 0 ° C and P = 36atm easily turns into a liquid state, then it is called carbon dioxide. From 1 l of liquid carbon dioxide at t ° = 0 ° 506 l of gas is formed. Stored in steel cylinders. The acid is supplied through the bells – diffusers, resulting in supercooling of the resulting acid and the formation of carbon dioxide.
When using carbon dioxide it is necessary to take into account its toxicity. Inhalation of air that contains 10% CO2 and has no odor causes respiratory paralysis and death.
Nitrogen has no color or odor. Compared with CO2, it turns into a liquid state at a very low temperature (-195.8 ° C).
Nitrogen as an extinguishing agent is used by the method of diluting the combustible substance.
Carbon dioxide and nitrogen are used in relatively small rooms, mainly for extinguishing flammable substances (liquids, gases). Poorly extinguishing substances that can smolder.
Because carbon dioxide is reduced by alkaline earth metals, it cannot be used to quench these metals.
Nitrogen is used to fill the free volumes in the vessels above the PPE in order to prevent explosions in production facilities.
Fire extinguishing foams are a mixture of gas and liquid. Gas bubbles can form inside the liquid as a result of chemical processes or mechanical mixing of gas (air) with the liquid. Foam damping is that the foam coating is as if a screen that prevents the heat of the combustion zone on the surface of the substance. The foam prevents the liquid from entering the combustion zone, showing an insulating effect. The foam also has some cooling effect.
Chemical foam is formed as a result of a reaction in which any gas is formed in a liquid medium. For example, foam generator powder is used to form foam, which contains an acidic part – alumina sulfate (Al2 (SO4) 3), an alkaline part – sodium bicarbonate (NaHCO3), licorice root extract (foaming agent that gives strength to films ). When the powder is mixed with water, it reacts to form carbon dioxide. This foam is used to extinguish petroleum products.
Air-mechanical foam is formed by mechanical mixing of air, water and surfactant (for example, foaming agent PO-1).
Foams are characterized by multiplicity and stability.
Multiplicity is the ratio of the volume of foam to the volume of liquid from which it is obtained. The multiplicity of chemical foam is 5. Air-mechanical foam is low (up to 10), medium (11-200) and high (201-1000) multiplicity.
Stability – the time from formation to complete disintegration. The stability of chemical foam is 40 minutes, air-mechanical – 20-30 minutes.
Low and medium multipurpose foams are used to extinguish petroleum products, solids and materials. High density foams are used to extinguish flammable and combustible substances.
Primary extinguishing agents:
internal fire hydrants; buckets, baskets, shovels, sand; fire extinguishers.
Foam fire extinguisher OHP-10 consists of a welded steel body, which contains an alkaline solution of soda with licorice extract. Inside is a plastic container with a mixture of sulfuric acid and ferrous sulfate. When mixing acidic and alkaline solutions, foam is formed. This fire extinguisher can be used to extinguish solids and flammable liquids with an open surface. The foam is electrically conductive, so this fire extinguisher cannot extinguish live electrical equipment.
Carbon dioxide fire extinguishers OU-2, OU-5 consist of a steel cylinder with a shut-off valve. The cylinder is filled with liquefied carbon dioxide at a pressure of 7 MPa. When the valve is opened, the liquefied carbon dioxide goes to the pipe, where it expands and due to this its temperature decreases to minus 70 ° C and snow-like carbon dioxide is formed. These fire extinguishers are used to extinguish small fires, live electrical equipment.
Alcohol and acetone, which dissolve carbon dioxide, as well as photographic film and celluloid, which burn without access to air, must not be extinguished.
Powder fire extinguishers OP-1, OP-5, OP-10, etc. – These are polyethylene cans that contain phosphorus-ammonium salts, sodium carbonate. They are used for extinguishing magnesium and its alloys, alkali metals, aluminum, organometallic compounds, as well as when you can not extinguish fires with water, foam or carbon dioxide.
Types of drugs and the concept of addiction. Abstract
Drug addicts are people without a future. They have lost their health and threaten the health of their own children and society. Addicts give birth to children with severe physical and mental disabilities. The addict’s appearance is far from attractive: gray face, dry skin, hair and teeth gradually fall out
The number of drug addicts is growing all over the world, including in Ukraine.