The composition of natural gas combustion products in percent. Combustion products of domestic gas and household activities. Change in burner load

Natural gas is the most widely used fuel today. Natural gas is called natural gas because it is extracted from the very bowels of the Earth.

The process of gas combustion is a chemical reaction in which natural gas interacts with oxygen contained in the air.

In gaseous fuel there is a combustible part and a non-combustible part.

The main combustible component of natural gas is methane - CH4. Its content in natural gas reaches 98%. Methane is odorless, tasteless and non-toxic. Its flammability limit is from 5 to 15%. It is these qualities that made it possible to use natural gas as one of the main types of fuel. The concentration of methane is more than 10% dangerous for life, so suffocation can occur due to lack of oxygen.

To detect a gas leak, the gas is subjected to odorization, in other words, a strong-smelling substance (ethyl mercaptan) is added. In this case, the gas can be detected already at a concentration of 1%.

In addition to methane, combustible gases such as propane, butane and ethane may be present in natural gas.

To ensure high-quality gas combustion, it is necessary to bring air into the combustion zone in sufficient quantities and achieve good mixing of gas with air. The ratio of 1: 10 is considered optimal. That is, ten parts of air fall on one part of the gas. In addition, it is necessary to create the desired temperature regime. In order for the gas to ignite, it must be heated to its ignition temperature and in the future the temperature should not fall below the ignition temperature.

It is necessary to organize the removal of combustion products into the atmosphere.

Complete combustion is achieved if there are no combustible substances in the combustion products released into the atmosphere. In this case, carbon and hydrogen combine together and form carbon dioxide and water vapor.

Visually, with complete combustion, the flame is light blue or bluish-violet.

In addition to these gases, nitrogen and the remaining oxygen enter the atmosphere with combustible gases. N 2 + O 2

If the combustion of gas is not complete, then combustible substances are emitted into the atmosphere - carbon monoxide, hydrogen, soot.

Incomplete combustion of gas occurs due to insufficient air. At the same time, tongues of soot appear visually in the flame.

The danger of incomplete combustion of gas is that carbon monoxide can cause poisoning of boiler room personnel. The content of CO in the air 0.01-0.02% can cause mild poisoning. Higher concentrations can lead to severe poisoning and death.

The resulting soot settles on the walls of the boilers, thereby worsening the transfer of heat to the coolant, which reduces the efficiency of the boiler house. Soot conducts heat 200 times worse than methane.

Theoretically, 9m3 of air is needed to burn 1m3 of gas. In real conditions, more air is needed.

That is, an excess amount of air is needed. This value, denoted alpha, shows how many times more air is consumed than theoretically necessary.

The alpha coefficient depends on the type of a particular burner and is usually prescribed in the burner passport or in accordance with the recommendations of the commissioning organization.

With an increase in the amount of excess air above the recommended one, heat losses increase. With a significant increase in the amount of air, flame separation can occur, creating an emergency. If the amount of air is less than recommended, then combustion will be incomplete, thereby creating a risk of poisoning the boiler room personnel.

For more accurate control of the quality of fuel combustion, there are devices - gas analyzers that measure the content of certain substances in the composition of exhaust gases.

Gas analyzers can be supplied with boilers. If they are not available, the relevant measurements are carried out by the commissioning organization using portable gas analyzers. A regime map is compiled in which the necessary control parameters are prescribed. By adhering to them, you can ensure the normal complete combustion of the fuel.

The main parameters for fuel combustion control are:

• the ratio of gas and air supplied to the burners.

• excess air ratio.

• crack in the furnace.

• Boiler efficiency factor.

At the same time, the efficiency of the boiler means the ratio of useful heat to the value of the total heat expended.

Composition of air

Combustion is a reaction in which the chemical energy of a fuel is converted into heat.

Burning can be complete or incomplete. Complete combustion occurs with sufficient oxygen. Lack of it causes incomplete combustion, in which less heat is released than with complete combustion, and carbon monoxide (CO), which is toxic to the operating personnel, forms soot that settles on the heating surface of the boiler and increases heat loss, which leads to excessive fuel consumption and a decrease in boiler efficiency, atmospheric pollution.

For the combustion of 1 m 3 of methane, 10 m 3 of air is needed, in which there is 2 m 3 of oxygen. For complete combustion of natural gas, air is supplied to the furnace with a slight excess. The ratio of the actual volume of air consumed V d to the theoretically necessary V t is called the excess air coefficient = V d / V t. This indicator depends on the design of the gas burner and furnace: the more perfect they are, the less. It is necessary to ensure that the excess air coefficient is not less than 1, as this leads to incomplete combustion of the gas. Increasing the excess air ratio reduces the efficiency of the boiler.

The completeness of fuel combustion can be determined using a gas analyzer and visually - by the color and nature of the flame:

transparent bluish - complete combustion;

red or yellow - incomplete combustion.

Combustion is controlled by increasing the air supply to the boiler furnace or by decreasing the gas supply. This process uses primary (mixes with gas in the burner - before combustion) and secondary (combines with gas or gas-air mixture in the boiler furnace during combustion) air.

In boilers equipped with diffusion burners (without forced air supply), the secondary air, under the action of vacuum, enters the furnace through the blower doors.

In boilers equipped with injection burners: primary air enters the burner due to injection and is regulated by an adjusting washer, and secondary air enters the burner through the blower doors.

In boilers with mixing burners, primary and secondary air is supplied to the burner by a fan and controlled by air dampers.

Violation of the ratio between the speed of the gas-air mixture at the outlet of the burner and the speed of flame propagation leads to separation or overshoot of the flame on the burners.

If the speed of the gas-air mixture at the outlet of the burner is greater than the speed of flame propagation - separation, and if less - slip.

In the event of a flame breaking off and flashing through, the operating personnel must extinguish the boiler, ventilate the furnace and gas ducts, and re-ignite the boiler.

Gaseous fuel every year finds more and more widespread use in various sectors of the national economy. In agricultural production, gaseous fuel is widely used for technological (for heating greenhouses, greenhouses, dryers, livestock and poultry complexes) and domestic purposes. Recently, it has been increasingly used for internal combustion engines.

Compared to other types of gaseous fuel, it has the following advantages:

burns in the theoretical amount of air, which ensures high thermal efficiency and combustion temperature;

when burned, it does not form undesirable products of dry distillation and sulfur compounds, soot and smoke;

it is relatively easy to be supplied through gas pipelines to remote objects of consumption and can be stored centrally;

easily ignites at any ambient temperature;

requires relatively low costs for extraction, which means that it is a cheaper type of fuel compared to other types of fuel;

can be used in compressed or liquefied form for internal combustion engines;

has high anti-knock properties;

does not form condensate during combustion, which provides a significant reduction in wear of engine parts, etc.

At the same time, gaseous fuel also has certain negative properties, which include: a toxic effect, the formation of explosive mixtures when mixed with air, easy flow through leaky joints, etc. Therefore, when working with gaseous fuel, careful observance of the relevant safety regulations is required.

The use of gaseous fuels is determined by their composition and properties of the hydrocarbon part. The most widely used are natural or associated gas from oil or gas fields, as well as factory gases from oil refineries and other plants. The main constituents of these gases are hydrocarbons with the number of carbon atoms in the molecule from one to four (methane, ethane, propane, butane and their derivatives).

Natural gases from gas fields consist almost entirely of methane (82...98%), with little use of gaseous fuel for internal combustion engines A constantly growing fleet of vehicles requires an increasing amount of fuel. It is possible to solve the most important national economic problems of stable provision of automobile engines with efficient energy carriers and reduction in the consumption of liquid fuels of petroleum origin through the use of gaseous fuels - liquefied petroleum and natural gases.

For cars, only high-calorie or medium-calorie gases are used. When operating on low-calorie gas, the engine does not develop the necessary power, and the driving range of the car is also reduced, which is economically unprofitable. Pa). They produce the following types of compressed gases: natural, mechanized coke and enriched coke

The main combustible component of these gases is methane. As well as for liquid fuel, the presence of hydrogen sulfide in gaseous fuel is undesirable because of its corrosive effect on gas equipment and engine parts. The octane number of gases allows boosting car engines in terms of compression ratio (up to 10 ... 12).

The presence of cyanide CN is highly undesirable in car gas. Combining with water, it forms hydrocyanic acid, under the influence of which tiny cracks form in the walls of the cylinders. The presence of tarry substances and mechanical impurities in the gas leads to the formation of deposits and pollution on gas equipment devices and on engine parts.

Combustion of a gas is a reaction of the combination of combustible gas components with oxygen in the air, accompanied by the release of heat. The combustion process depends on the chemical composition of the fuel. The main component of natural gas is methane, but ethane, propane and butane are also combustible, which are contained in small quantities.

Natural gas produced from West Siberian deposits almost completely (up to 99%) consists of CH4 methane. Air consists of oxygen (21%) and nitrogen and a small amount of other non-combustible gases (79%). Simplified, the reaction of complete combustion of methane is as follows:

CH4 + 2O2 + 7.52 N2 = CO2 + 2H20 + 7.52 N2

As a result of the combustion reaction during complete combustion, carbon dioxide CO2 is formed, and water vapor H2O is a substance that does not have a harmful effect on the environment and humans. Nitrogen N does not participate in the reaction. For complete combustion of 1 m³ of methane, 9.52 m³ of air is theoretically required. For practical purposes, it is considered that for the complete combustion of 1 m³ of natural gas, at least 10 m³ of air is needed. However, if only the theoretically necessary amount of air is supplied, then it is impossible to achieve complete combustion of the fuel: it is difficult to mix the gas with air in such a way that the required number of oxygen molecules is supplied to each of its molecules. In practice, more air is supplied to combustion than theoretically necessary. The amount of excess air is determined by the coefficient of excess air a, which shows the ratio of the amount of air actually consumed for combustion to the theoretically required amount:

α = V fact./V theor.

where V is the amount of air actually used for combustion, m³;
V is the theoretically required amount of air, m³.

The excess air coefficient is the most important indicator characterizing the quality of gas combustion by the burner. The smaller a, the less heat will be carried away by the exhaust gases, the higher the efficiency of the gas-using equipment. But burning the gas with insufficient excess air results in a lack of air, which can cause incomplete combustion. For modern burners with complete pre-mixing of gas with air, the excess air coefficient lies in the range of 1.05 - 1.1 ", that is, air is consumed for combustion by 5 - 10% more than theoretically required.

With incomplete combustion, the combustion products contain a significant amount of carbon monoxide CO, as well as unburned carbon in the form of soot. If the burner works very poorly, then the combustion products may contain hydrogen and unburned methane. Carbon monoxide CO (carbon monoxide) pollutes the air in the room (when using equipment without exhausting combustion products into the atmosphere - gas stoves, columns of low thermal power) and has a toxic effect. Soot contaminates heat exchange surfaces, sharply reduces heat transfer and reduces the efficiency of household gas-using equipment. In addition, when using gas stoves, dishes are contaminated with soot, which requires considerable effort to remove. In water heaters, soot pollutes the heat exchanger, in “neglected” cases, almost to the complete cessation of heat transfer from combustion products: the column burns, and the water heats up by several degrees.

Incomplete combustion occurs:

• with insufficient air supply for combustion;
• with poor mixing of gas and air;
• with excessive cooling of the flame before the completion of the combustion reaction.

The quality of gas combustion can be controlled by the color of the flame. Poor-quality gas combustion is characterized by a yellow smoky flame. When the gas is completely burned, the flame is a short torch of a bluish-violet color with a high temperature. To control the operation of industrial burners, special devices are used that analyze the composition of flue gases and the temperature of the combustion products. At present, when adjusting certain types of household gas-using equipment, it is also possible to regulate the combustion process by temperature and analysis of flue gases.

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Characteristics of methane

§ Colorless;

§ Non-toxic (not poisonous);

§ Odorless and tasteless.

§ The composition of methane includes 75% carbon, 25% hydrogen.

§ The specific gravity is 0.717 kg / m 3 (2 times lighter than air).

§ Flash point is the minimum initial temperature at which combustion begins. For methane, it is equal to 645 o.

§ combustion temperature- this is the maximum temperature that can be reached with complete combustion of the gas, if the amount of air required for combustion exactly corresponds to the chemical formulas of combustion. For methane, it is equal to 1100-1400 o and depends on the combustion conditions.

§ Heat of combustion- this is the amount of heat that is released during the complete combustion of 1 m 3 of gas and it is equal to 8500 kcal / m 3.

§ Flame spread rate equal to 0.67 m/s.

Gas-air mixture

In which the gas is located:

Up to 5% does not burn;

5 to 15% explodes;

Over 15% burns when additional air is supplied (all this depends on the ratio of the volume of gas in the air and is called explosive limits)

Combustible gases are odorless, for their timely detection in the air, quick and accurate detection of leaks, the gas is odorized, i.e. give off a scent. To do this, use ETHYLMERKOPTAN. The odorization rate is 16 g per 1000 m 3. If there is 1% natural gas in the air, its smell should be felt.

The gas used as fuel must comply with the requirements of GOST and contain harmful impurities per 100m 3 no more than:

Hydrogen sulfide 0.0 2 G /m.cube

Ammonia 2 gr.

Hydrocyanic acid 5 gr.

Resin and dust 0.001 g/m3

Naphthalene 10 gr.

Oxygen 1%.

The use of natural gas has several advantages:

absence of ash and dust and removal of solid particles into the atmosphere;

high calorific value;

· convenience of transportation and burning;

facilitating the work of maintenance personnel;

· Improvement of sanitary and hygienic conditions in boiler houses and adjacent areas;

Wide range of automatic control.

When using natural gas, special precautions are required, as possible leakage through leaks at the junction of the gas pipeline and fittings. The presence of more than 20% of gas in the room causes suffocation, its accumulation in a closed volume of more than 5% to 15% leads to an explosion of the gas-air mixture. Incomplete combustion produces carbon monoxide, which, even at low concentrations (0.15%), is poisonous.

Burning natural gas

burning is called the rapid chemical combination of combustible parts of the fuel with oxygen in the air, occurs at high temperature, is accompanied by the release of heat with the formation of a flame and combustion products. Burning happens complete and incomplete.

Full burning Occurs when there is sufficient oxygen. The lack of oxygen causes incomplete combustion, at which a smaller amount of heat is released than at full, carbon monoxide (poisonous effect on maintenance personnel), soot is formed on the surface of the boiler and heat losses increase, which leads to excessive fuel consumption, reduced boiler efficiency, atmospheric pollution.

The combustion products of natural gas are– carbon dioxide, water vapor, some excess oxygen and nitrogen. Excess oxygen is contained in combustion products only in those cases when combustion occurs with excess air, and nitrogen is always contained in combustion products, because. is an integral part of air and does not take part in combustion.

The products of incomplete combustion of gas can be carbon monoxide, unburned hydrogen and methane, heavy hydrocarbons, soot.

Methane reaction:

CH 4 + 2O 2 \u003d CO 2 + 2H 2 O

According to the formula for the combustion of 1 m 3 of methane, 10 m 3 of air is needed, in which there is 2 m 3 of oxygen. In practice, for burning 1 m 3 of methane, more air is needed, taking into account all kinds of losses, for this a coefficient is applied To excess air, which = 1.05-1.1.

Theoretical air volume = 10 m 3

Practical air volume = 10*1.05=10.5 or 10*1.1=11

Completeness of combustion fuel can be determined visually by the color and nature of the flame, as well as using a gas analyzer.

Transparent blue flame - complete combustion of gas;

Red or yellow with smoky streaks - combustion is incomplete.

Combustion is controlled by increasing the air supply to the furnace or decreasing the gas supply. This process uses primary and secondary air.

secondary air– 40-50% (mixed with gas in the boiler furnace during combustion)

primary air– 50-60% (mixed with gas in the burner before combustion) gas-air mixture is used for combustion

Combustion characterizes flame spread rate is the speed at which the element of the flame front spreads relatively fresh jet of air-gas mixture.

The rate of combustion and flame propagation depends on:

from the composition of the mixture;

on temperature;

from pressure;

on the ratio of gas and air.

The burning rate determines one of the main conditions for the reliable operation of the boiler house and characterizes it flame separation and breakthrough.

Flame break- occurs if the speed of the gas-air mixture at the outlet of the burner is greater than the combustion speed.

Reasons for separation: excessive increase in gas supply or excessive vacuum in the furnace (draught). Flame separation is observed during ignition and when the burners are turned on. The separation of the flame leads to the gas contamination of the furnace and gas ducts of the boiler and to an explosion.

Flashlight- occurs if the flame propagation speed (burning speed) is greater than the speed of the gas-air mixture outflow from the burner. The breakthrough is accompanied by the combustion of the gas-air mixture inside the burner, the burner heats up and fails. Sometimes the breakthrough is accompanied by a pop or explosion inside the burner. In this case, not only the burner, but also the front wall of the boiler can be destroyed. Overshoot occurs when the gas supply is sharply reduced.

When the flame breaks off and flashes, the maintenance personnel must stop the fuel supply, find out and eliminate the cause, ventilate the furnace and gas ducts for 10-15 minutes and rekindle the fire.

The combustion process of gaseous fuel can be divided into 4 stages:

1. Outflow of gas from the burner nozzle into the burner under pressure at an increased rate.

2. Formation of a mixture of gas with air.

3. Ignition of the resulting combustible mixture.

4. Combustion of a combustible mixture.

Gas pipelines

Gas is supplied to the consumer through gas pipelines - external and internal- to gas distribution stations located outside the city, and from them through gas pipelines to gas control points hydraulic fracturing or gas control devices GRU industrial enterprises.

Gas pipelines are:

· high pressure first category over 0.6 MPa up to 1.2 MPa inclusive;

· high pressure second category over 0.3 MPa to 0.6 MPa;

· medium pressure third category over 0.005 MPa to 0.3 MPa;

· low pressure category 4 up to 0.005 MPa inclusive.

MPa means Mega Pascal

Only medium and low pressure gas pipelines are laid in the boiler room. The section from the distribution gas pipeline of the network (city) to the premises, together with the disconnecting device, is called input.

The inlet gas pipeline is considered the section from the disconnecting device at the inlet, if it is installed outside the premises to the internal gas pipeline.

At the gas inlet to the boiler room in a lighted and convenient place for maintenance, there must be a valve. There must be an insulating flange in front of the valve to protect against stray currents. At each branch from the gas distribution pipeline to the boiler, at least 2 disconnecting devices are provided, one of which is installed directly in front of the burner. In addition to fittings and instrumentation on the gas pipeline, in front of each boiler, an automatic device must be installed to ensure the safe operation of the boiler. In order to prevent the ingress of gases into the boiler furnace, if the shut-off devices are faulty, purge candles and safety gas pipelines with shut-off devices are required, which must be open when the boilers are inactive. Low-pressure gas pipelines are painted yellow in boiler houses, and medium-pressure gas pipelines are painted yellow with red rings.

Gas-burners

Gas-burners- a gas burner designed to supply to the place of combustion, depending on the technological requirements, a prepared gas-air mixture or separated gas and air, as well as to ensure stable combustion of gaseous fuel and control the combustion process.

Burners are subject to the following requirements:

· the main types of burners must be mass-produced at factories;

burners must ensure the passage of a given amount of gas and the completeness of its combustion;

ensure the minimum amount of harmful emissions into the atmosphere;

must work without noise, separation and flashover of the flame;

should be easy to maintain, convenient for revision and repair;

if necessary, could be used for reserve fuel;

· samples of newly created and operating burners are subject to GOST testing;

The main characteristic of the burners is its thermal power, which is understood as the amount of heat that can be released during the complete combustion of the fuel supplied through the burner. All these characteristics can be found in the burner data sheet.

Alexander Pavlovich Konstantinov

Chief Inspector for Safety Control of Nuclear and Radiation Hazardous Facilities. Candidate of Technical Sciences, Associate Professor, Professor of the Russian Academy of Natural Sciences.

A kitchen with a gas stove is often the main source of air pollution in an entire apartment. And, what is very important, this applies to the majority of the inhabitants of Russia. Indeed, in Russia, 90% of urban and over 80% of rural residents use gas stoves Khata, Z. I. Human health in the modern ecological situation. - M. : FAIR-PRESS, 2001. - 208 p..

In recent years, there have been publications of serious researchers about the high danger of gas stoves for health. Doctors know that in houses where gas stoves are installed, residents get sick more often and longer than in houses with electric stoves. And we are talking about many different diseases, and not just about diseases of the respiratory tract. The decrease in the level of health is especially noticeable in women, children, as well as in the elderly and chronically ill people who spend more time at home.

Professor V. Blagov knowingly called the use of gas stoves "large-scale chemical warfare against their own people."

Why is the use of household gas harmful to health

Let's try to answer this question. There are several factors that together make the use of gas stoves hazardous to health.

The first group of factors

This group of factors is due to the very chemistry of the natural gas combustion process. Even if household gas burned completely to water and carbon dioxide, this would lead to a deterioration in the composition of the air in the apartment, especially in the kitchen. After all, at the same time, oxygen is burned out of the air, while the concentration of carbon dioxide increases. But this is not the main problem. In the end, the same thing happens with the air that a person breathes.

It is much worse that in most cases the combustion of gas does not occur completely, not 100%. Due to the incomplete combustion of natural gas, much more toxic products are formed. For example, carbon monoxide (carbon monoxide), the concentration of which can be many times, 20–25 times higher than the permissible norm. But this leads to headaches, allergies, ailments, weakened immunity. Yakovleva, M. A. We have gas in our apartment. - Business environmental magazine. - 2004. - No. 1(4). - S. 55..

In addition to carbon monoxide, sulfur dioxide, nitrogen oxides, formaldehyde, and benzpyrene, a strong carcinogen, are released into the air. In cities, benzpyrene enters the atmospheric air from emissions from metallurgical enterprises, thermal power plants (especially coal-fired) and cars (especially old ones). But the concentration of benzpyrene, even in polluted atmospheric air, cannot be compared with its concentration in an apartment. The figure shows how much more benzpyrene we get while in the kitchen.

Let's compare the first two columns. In the kitchen, we get 13.5 times more harmful substances than on the street! For clarity, let's estimate the intake of benzpyrene in our body not in micrograms, but in a more understandable equivalent - the number of cigarettes smoked daily. So, if a smoker smokes one pack (20 cigarettes) per day, then in the kitchen a person receives the equivalent of two to five cigarettes per day. That is, the hostess, who has a gas stove, seems to “smoke” a little.

The second group of factors

This group is related to the operating conditions of gas stoves. Any driver knows that it is impossible to be in the garage at the same time as the car with the engine running. But in the kitchen we have just such a case: the combustion of hydrocarbon fuels indoors! We do not have the device that every car has - an exhaust pipe. According to all the rules of hygiene, each gas stove must be equipped with an exhaust ventilation umbrella.

Things are especially bad if we have a small kitchen in a small apartment. A meager area, minimal ceiling height, poor ventilation and a gas stove running all day. But with low ceilings, gas combustion products accumulate in the upper layer of air up to 70–80 centimeters thick. Boyko, A. F. Health 5+. - M. : Rossiyskaya Gazeta, 2002. - 365 p..

Often, the work of a housewife at a gas stove is compared with harmful working conditions in the workplace. This is not entirely correct. Calculations show that if the kitchen is small, and there is no good ventilation, then we are dealing with particularly harmful working conditions. Type of metallurgist serving coke batteries.

How to reduce the harm from a gas stove

How can we be, if everything is so bad? Maybe it's really worth getting rid of the gas stove and installing an electric or induction one? Well, if there is such an opportunity. And if not? There are a few simple rules for this. It is enough to observe them, and you can reduce the harm to health from a gas stove dozens of times. We list these rules (most of them are the recommendations of Professor Yu. D. Gubernsky) Ilnitsky A. Smells like gas. - Be healthy!. - 2001. - No. 5. - S. 68–70..

1. It is necessary to install an exhaust hood with an air cleaner above the stove. This is the most effective approach. But even if for some reason you cannot do this, then the remaining seven rules in total will also significantly reduce air pollution.
2. Monitor the completeness of combustion of gas. If suddenly the color of the gas is not what it should be according to the instructions, immediately call the gas workers to regulate the broken burner.
3. Do not clutter the stove with extra dishes. Cookware should only be placed on the burners that are running. In this case, free access of air to the burners and more complete combustion of the gas will be ensured.
4. It is better to use no more than two burners or an oven and one burner at the same time. Even if your stove has four burners, it's best to turn on a maximum of two at the same time.
5. The maximum time of continuous operation of the gas stove is two hours. After that, you need to take a break and thoroughly ventilate the kitchen.
6. During the operation of the gas stove, the doors to the kitchen must be closed and the window open. This will ensure that the products of combustion are removed through the street, and not through the living rooms.
7. After the end of the gas stove, it is advisable to ventilate not only the kitchen, but the entire apartment. Cross-ventilation is desirable.
8. Never use a gas stove to heat or dry laundry. You wouldn't start a fire in the middle of the kitchen for this purpose, would you?