【 Weak current College 】 live equipment fire extinguishing agent selection and application

With economic development and social progress, the power of popular in-depth millions, widely used in various areas of society. Each of the electrical and fire case too numerous to mention, to the countries and peoples of economic loss and very serious casualties. Electrical fire spread rapidly after burning, fighting is difficult. Conditions permitting, should generally be used off fire method, but in the actual fire fighting, often because they are waiting to be powered off and lose the best fire extinguishing time, or because of power outages and seriously affecting production, to take effective live fire suppression methods that you can respond quickly and effectively to control the fire, the fire extinguished, reduced disaster losses. Fire and safety precautions correctly or not, have a direct bearing on the success or failure of a charged fire fighting. The author according to the electrical theory knowledge combined with practice is charging the device at the scene, the line of fire extinguishing agent in the use and safety precautions for a discussion with fellow.

First, use not conductive agent charged fire-extinguishing

As a result of water, foam and other fire extinguishing agent is the conductors in the fight live fire-fighting personnel, easily lead to electric shock, therefore, need not be used in fire-fighting. The scene is often used on conductive agent are:

(A) dry powder. Powder extinguishing agent from potassium and sodium carbonate class joined additive such as talcum powder, diatomaceous earth, not conductive extinguishers have artificial throwing and compressed gas injection. Principle is suppressed combustion, burning of dry powder can be generated by the activity group for OH, etc, make it a non-active substances, so that combustion chain cannot continue, so as to achieve the effect of extinguishing fire. Powder extinguishing agent not to fight with rotating machinery electrical equipment and afraid of fire extinguishing agent defaced precision electrical equipment fire.

(2) carbon dioxide. Carbon dioxide fire extinguishing agent is completely normal temperature of combustion products, is a colorless, tasteless, non-conductive gas, non-corrosive to the device, in the case of no gas. Relative air density 1.5, liquid state into a fire extinguisher cylinder, extremely volatile, room temperature maintaining 60kg/c © o pressure, liquid carbon dioxide injection, volume expansion of 400-700 times, intense heat absorption cooling, condensation rime ice, as in the combustion zone directly into gas, heat absorption cooling air to the combustion of isolation, so as to achieve fire extinguishing purposes. Carbon dioxide gas is easy to use by suffocating, should be in the upper hand when people or side wind direction, while the hand fire extinguishers should be held to prevent dry ice contacts handles the human cause frostbite.

(3) carbon tetrachloride. Carbon tetrachloride fire extinguishing agent is a colorless, flammable liquid, not spontaneous, not combustion, non conductive, relative density 1.6, boiling point, vapour density 76.8 ¡æ about air 5.5 times. When a liquid spray to the burning of carbon tetrachloride, rapid thermal gasification, vapor makes burning and oxygen, thus allowing combustion to abort. Carbon tetrachloride in the air concentration reaches 10% of the time, you can put out a fire. But with carbon tetrachloride toxicity, high temperatures and water vapor and other substances very toxic gases in the role, therefore, should be used to wear gas masks, people want to wind or side wind direction in case of poisoning.

(4) of the 1211 fire-extinguishing agent. 1211 fire-extinguishing agent often become the liquid state is mounted fire extinguisher cylinder, divided into portable and fixed nozzle unit. It is an efficient, low toxicity, corrosivity and fire back without leaving any traces, non conductive, using secure, long storage life. It can prevent combustion chain reaction, and have a certain amount of cooling and suffocation role fighting electrical equipment, precision instruments and fire have special effects that can be composed with fire alarm equipment, fixed fire extinguishing systems for control rooms, transformer, electronic, computer, cable tunnels automatic fire extinguishing.

Second, the use of water as an extinguishing agent charged fire-extinguishing

Water is cheap and widespread fire extinguishing agent.

Specific heat in standard atmospheric pressure, water evaporation per kg of boiling 539KJ to absorb heat. Water cooling, fire extinguishing efficiency is high, is commonly used for fire extinguishing agent. But water conductivity, live in the water used in fire extinguishing equipment, charged body, water, and Earth would form the electrical circuit, prone to electric shock accident. According to the test, when the current passes through the body to 1mA, person feel there is electricity. So as long as you are familiar with the impact factors of leakage current size, the water leakage current control in the following, to 1mA to protect the safety of the personnel of fighting, live firefighting personnel does not have any sensation.

(A) water gun nozzle diameter size of leakage current. Different water gun nozzle diameter formed by water column section is different, then change the water resistance, nozzle small, large and small; nozzle section, section. If the fire is charged voltage must comply with the leakage current size, if the law of Ohm's law nozzle diameter must, leakage current is less than 1mA, corresponding to certain nozzle, can determine the minimum safe distance to the water column. The same as the voltage, the electrical resistivity of water, the distance equal to the same conditions, using small-caliber gun, by the water leakage current is large-diameter. In the scene on a DC gun for live fire, if the voltage is high, or more hours of resistivity of water, in order to increase the security level, the use of small-caliber gun. If you need to increase the fire-fighting water consumption, you can increase the number of small caliber gun without having to switch to large calibre gun.

(2) water pressure and water gun Jet in the form of leakage current size. When the pump pressure increases, the nozzle size must, from the DC gun shoot out of the full water column, the corresponding growth in the water column dense, current easier through, leakage current is as pressure grows, but through flowering water gun shot, the greater the pressure of the water pump, water and fire water droplets scattered have better water droplets, the more evenly between gap and a corresponding increase in resistance, and the leakage current is reduced accordingly. But through the spray gun shot, pump pressure, the greater the flow of atomization of better water jet in the bubble, the resistor increases, leakage current is reduced accordingly. Therefore, in the scene, using DC gun live fire, near from the charged body, should not be tooHigh pressure; the use of flowering water gun, should not be used for low pressure; the use of spray gun live fire, pressure must be ＞ 7Kg, thus ensuring that there is sufficient water pressure, ensuring adequate atomization and resistance values.

(3) water resistivity on the effect of the leakage current size. Different media with different resistivity, its electrical conductivity varies with impurities. Use water resistivity of water quality for live fire, the water resistance is large, the water leakage current is small, so you can increase the security level. Use chemical pure water does not conduct electricity, but in reality it is not possible.

(4) water gun nozzle-charged body of distance on the effect of the leakage current size. Water gun nozzle to live in the greater the distance, the longer the water column, the greater the resistance to the water column, while the water leakage current is less. Therefore, in the scene, if you live in DC gun fire, it can give full play to the DC gun onger, appropriate to increase the water gun nozzle to the distance between the charged body, to increase water-use the security level of a charged fire-extinguishing, may also be appropriate to direct DC gun fire.

(5) charged voltage on leakage current size. In the scene on the DC gun fire, if the voltage of the charged body, through the water leakage current is relatively large. Therefore it is necessary to pay attention to water gun nozzle to the distance between the charged body.

3. when a charged fire should do security precautions

Fire extinguishing live is a dangerous job, fire commanders to a holistic view of the fire site, and do various security measures to ensure that safety organizations implement fire-fighting work.

(A) to wear protective equipment: live-fire fighting, rescue personnel should wear insulated shoes to prevent foot and leg parts in contact with charged bodies. To wear insulated gloves, prevent hand direct contact with charged bodies; conditions firefighting personnel should wear are subdued, wear are subdued to the hats, socks, gloves, shoes with copper and brass buckle connected to each other as a whole.

(2) set the grounding device: metal water gun nozzle, install the grounding line by section 5 ~ 10m square meters of copper wire for earth connection, more than with long 1m 50mm（diameter） steel pipe or 50 × 50mm of steel angle for grounding rods, grounding line ends with the water gun nozzle and grounding rods firmly connected. And the best nail grounding rods into the soil underneath 0.5m, requirements should not be too dry, and in the grounding rods Department into the brine or ordinary water to grounding and conductor connect, between * daochu water gun on current. In addition, the lightning rod down lead and take over tap water, metal heating pipes, Poles, cables can be used as a grounding device.

(3) a minimum safety distance: minimum safety distance refers to the human body through the leakage current of less than 1mA keep a minimum distance. Implementing a live fire fighting, rescue personnel and the use of fire fighting equipment to and live parts maintain sufficient distance, the higher the voltage, the greater the distance. The distance from voltage 10KV, charged body to maintain the minimum distance shall be not less than 40cm. when indoor high voltage electrical apparatus or circuits at the time of the grounding occurred, its surrounding context, fighting 4m shall * close, such as outdoor, its surrounding 8m within, the personnel shall not close. In the water when a charged fire-extinguishing, regardless of what action to take, the general minimum safety distance should be kept in ≮ 5m; fire extinguishing transformer, fighting personnel station location of ground-level distance and charged body height on the angle of 45 ° ≯ should be. In fighting the fire overhead electrified lines, fire-fighting personnel and charged body wire between 45 ° elevation should ≯ and should stand in line outside to prevent wire broken backward drop touch human-caused casualties. Overhead wire break down in water can reach fire points, between the man and charged body should try to keep the large horizontal distance from the wire breaking, to wipe the warning area of prohibition.

(4) to avoid human contact with charged bodies: in the water when a charged fire fighting, rescue personnel of the body parts do not touch DC gun shot to the charged body of water to prevent leakage current through the body into the ground; no grounding line of cases, the use of plastic water gun, further improving insulation strength; to live equipment water, the water gunmen wearing rubber boots for General should, in fire-fighting cylinders, prevent water inflow boots, other staff to prevent contact with water; use DC gun fire during discharge or discharge, shock sensor, taken in supine position shooting water, the water zone and water gun metal contact of the Department of medicine, so as to avoid electric shock wounding; breaking, to prevent the tool and charged body contact. There is no protective appliances, personnel and should not be close to the combustion zone, to prevent the risk of surface water stains have conductive;

(5) as far as possible the flow of atomization of high pressure water gun. High pressure water gun caliber usually 6.5mm, 7.0mm, 7.5mm, 8.0mm, work pressure, its corresponding 4MPa range 9m, 11m, 12m, 15m, droplets of diameter 100-200um and selected according to voltage, the normal flow of atomization distance before the charged body for fire suppression. Practice shows that the distance fog nozzle nozzles 1.5m charged body, and greater than 7.07 × 105Pa pressure under fire, no leakage current. Spray gun off transformer fire requires water gunmen casually swing, it is better to use two gun compared with strong coverage of spray flow will fire extinguishing suffocation.

(6) the reasonable use of Jet forms: use copper grid instead of the grounding rods cannot be used. As far as possible, a charged fire-extinguishing spray of water spray flow can not grounded, but according to the voltage size selected and charged body safe distance, fire pump pressure keep 0.5 ~ 0.7MPa. direct use enrich the water with live fire. Use of large diameter water gun, using spot for long distance shooting water fire extinguishing or make the water flow is a parabola-shaped falls fire points, increasing water column length.