Relationship between oxygen and fire hazard

Home oxygen and domestic fires

relationship between oxygen and fire hazard

EUROPEAN INDUSTRIAL GASES ASSOCIATION AISBL .. description of the fire and explosion hazards associated with oxygen and oxygen enriched. Include a careful examination of the risks from using oxygen in your risk it becomes easier to start a fire, which will then burn hotter and more fiercely. □ .. acetylene) CP4(rev3) Code of Practice British Compressed Gases Association Oxygen enrichment of the atmosphere, even by a few percent, considerably increases the risk of fire. Sparks which would normally be regarded as harmless can.

The following ten points have been gleaned from NFPA statistics over the period to Cote Home smoke detectors are widely used and very effective but significant gaps in the detector strategy remain. Automatic sprinklers produce large reductions in loss of life and property. Increased use of portable and area heating equipment sharply increased home fires involving heating equipment.

A large share of fire-fighter fatalities are attributed to heart attacks and activities away from the fireground. Rural areas have the highest fire death rates. Smoking materials igniting upholstered furniture, mattresses or bedding produce the most deadly residential fire scenarios. US and Canadian fire death rates are amongst the highest of all the developed countries.

The states of the Old South in the United States have the highest fire death rates. Older adults are at particularly high risk of death in fire. Such conclusions are, of course, country-specific, although there are some common trends. Careful use of such data can provide the means of formulating sound policies regarding fire safety in the community.

Proactive measures can only be introduced following a detailed fire hazard assessment. Such a course of action has been introduced progressively, starting in the nuclear industry and moving into the chemical, petrochemical and offshore industries where the risks are much more easily defined than in other industries.

relationship between oxygen and fire hazard

Their application to hotels and public buildings generally is much more difficult and requires the application of fire modelling techniques to predict the course of a fire and how the fire products will spread through the building to affect the occupants. Major advances have been made in this type of modelling, although it must be said that there is a long way to go before these techniques can be used with confidence.

Fire safety engineering is still in need of much basic research in fire safety science before reliable fire hazard assessment tools can be made widely available.

For our purposes, the most important statements in connection with combustion, as a phenomenon, are as follows: Ignition may be considered the first step of the self-sustaining process of combustion. It may occur as piloted ignition or forced ignition if the phenomenon is caused by any outer ignition source, or it may occur as auto ignition or self ignition if the phenomenon is the result of reactions taking place in the combustible material itself and coupled with heat release.

The inclination to ignition is characterized by an empirical parameter, the ignition temperature i. In the case of piloted ignition, the energy required for the activation of the materials involved in the burning reaction is supplied by ignition sources. However, there is no direct relationship between the heat quantity needed for ignition and the ignition temperature, because although the chemical composition of the components in the combustible system is an essential parameter of ignition temperature, it is considerably influenced by the sizes and shapes of materials, the pressure of the environment, conditions of air flow, parameters of ignition source, the geometrical features of the testing device, etc.

This is the reason for which the data published in literature for autoignition temperature and piloted ignition temperature can be significantly different.

The ignition mechanism of materials in different states may be simply illustrated.


This involves examining materials as either solids, liquids or gases. Most solid materials take up energy from any outer ignition source either by conduction, convection or radiation mostly by their combinationor are heated up as a result of the heat-producing processes taking place internally that start decomposition on their surfaces.

For ignition to occur with liquids, these must have the formation of a vapour space above their surface that is capable of burning. The vapours released and the gaseous decomposition products mix with the air above the surface of liquid or solid material. The particles induced enter into interaction, resulting in the release of heat.

The process steadily accelerates, and as the chain reaction starts, the material comes to ignition and burns. The combustion in the layer under the surface of solid combustible materials is called smouldering, and the burning reaction taking place on the interface of solid materials and gas is called glowing.

Burning with flames or flaming is the process in the course of which the exothermic reaction of burning runs in the gas phase. This is typical for the combustion of both liquid and solid materials. Combustible gases burn naturally in the gas phase. It is an important empirical statement that the mixtures of gases and air are capable of ignition in a certain range of concentration only.

This is valid also for the vapours of liquids. The lower and upper flammable limits of gases and vapours depend on the temperature and pressure of the mixture, the ignition source and the concentration of the inert gases in the mixture. Ignition Sources The phenomena supplying heat energy may be grouped into four fundamental categories as to their origin Sax The following discussion addresses the most frequently encountered sources of ignition.

Open flames Open flames may be the simplest and most frequently used ignition source. A large number of tools in general use and various types of technological equipment operate with open flames, or enable the formation of open flames. Burners, matches, furnaces, heating equipment, flames of welding torches, broken gas and oil pipes, etc.

Because with an open flame the primary ignition source itself represents an existing self-sustaining combustion, the ignition mechanism means in essence the spreading of burning to another system. Provided that the ignition source with open flame possesses sufficient energy for initiating ignition, burning will start.

The materials inclined to spontaneous heating and spontaneous ignition may, however, become secondary ignition sources and give rise to ignition of the combustible materials in the surroundings. Although some gases e. Spontaneous ignition, like all ignitions, depends on the chemical structure of the material, but its occurrence is determined by the grade of dispersity. The large specific surface enables the local accumulation of reaction heat and contributes to the increase of temperature of material above spontaneous ignition temperature.

Spontaneous ignition of liquids is also promoted if they come into contact with air on solid materials of large specific surface area. Fats and especially unsaturated oils containing double bonds, when absorbed by fibrous materials and their products, and when impregnated into textiles of plant or animal origin, are inclined to spontaneous ignition under normal atmospheric conditions.

Spontaneous ignition of glass-wool and mineral-wool products produced from non-combustible fibres or inorganic materials covering large specific surfaces and contaminated by oil have caused very severe fire accidents. Spontaneous ignition has been observed mainly with dusts of solid materials. For metals with good heat conductivity, local heat accumulation needed for ignition necessitates very fine crushing of metal. As the particle size decreases, the likelihood of spontaneous ignition increases, and with some metal dusts for example, iron pyrophorosity ensues.

When storing and handling coal dust, soot of fine distribution, dusts of lacquers and synthetic resins, as well as during the technological operations carried out with them, special attention should be given to the preventive measures against fire to reduce the hazard of spontaneous ignition. Materials inclined to spontaneous decomposition show special ability to ignite spontaneously. Hydrazine, when set on any material with a large surface area, bursts into flames immediately. The peroxides, which are widely used by the plastics industry, easily decompose spontaneously, and as a consequence of decomposition, they become dangerous ignition sources, occasionally initiating explosive burning.

The violent exothermic reaction that occurs when certain chemicals come into contact with each other may be considered a special case of spontaneous ignition. Examples of such cases are contact of concentrated sulphuric acid with all the organic combustible materials, chlorates with sulphur or ammonium salts or acids, the organic halogen compounds with alkali metals, etc.

It is worth mentioning that such hazardously high spontaneous heating may, in some cases, be due to the wrong technological conditions insufficient ventilation, low cooling capacity, discrepancies of maintenance and cleaning, overheating of reaction, etc.

Certain agricultural products, such as fibrous feedstuffs, oily seeds, germinating cereals, final products of the processing industry dried beetroot slices, fertilizers, etc. The spontaneous heating of these materials has a special feature: Electric ignition sources Power machines, instruments and heating devices operated by electric energy, as well as the equipment for power transformation and lighting, typically do not present any fire hazard to their surroundings, provided that they have been installed in compliance with the relevant regulations of safety and requirements of standards and that the associated technological instructions have been observed during their operation.

Regular maintenance and periodic supervision considerably diminish the probability of fires and explosions.

Chemistry 101: Oxygen is not flammable

The most frequent causes of fires in electric devices and wiring are overloading, short circuits, electric sparks and high contact resistances. Overloading exists when the wiring and electrical appliances are exposed to higher current than that for which they are designed.

The overcurrent passing through the wiring, devices and equipment might lead to such an overheating that the overheated components of the electrical system become damaged or broken, grow old or carbonize, resulting in cord and cable coatings melting down, metal parts glowing and the combustible structural units coming to ignition and, depending on the conditions, also spreading fire to the environment. The most frequent cause of overloading is that the number of consumers connected is higher than permitted or their capacity exceeds the value stipulated.

The working safety of electrical systems is most frequently endangered by short circuits. They are always the consequences of any damage and occur when the parts of the electrical wiring or the equipment at the same potential level or various potential levels, insulated from each other and the earth, come into contact with each other or with the earth.

This contact may arise directly as metal-metal contact or indirectly, through electric arc.

relationship between oxygen and fire hazard

In cases of short circuits, when some units of the electric system come in contact with each other, the resistance will be considerably lower, and as a consequence, the intensity of current will be extremely high, perhaps by several orders of magnitude higher.

The heat energy released during overcurrents with large short circuits might result in a fire in the device affected by the short circuit, with the materials and equipment in the surrounding area coming to ignition and with the fire spreading to the building. Electric sparks are heat energy sources of a small nature, but as shown by experience, act frequently as ignition sources.

Under normal working conditions, most electrical appliances do not release sparks, but the operation of certain devices is normally accompanied by sparks. Sparking introduces a hazard foremost at places where, in the zone of their generation, explosive concentrations of gas, vapour or dust might arise. Consequently, equipment normally releasing sparks during operation is permitted to be set up only at places where the sparks cannot give rise to fire.

On its own, the energy content of sparks is insufficient for the ignition of the materials in the environment or to initiate an explosion. If an electrical system has no perfect metallic contact between the structural units through which the current flows, high contact resistance will occur at this spot.

This phenomenon is in most cases due to the faulty construction of joints or to unworkmanlike installations. The disengagement of joints during operation and natural wear may also be cause for high contact resistance.

A large portion of the current flowing through places with increased resistance will transform to heat energy. If this energy cannot be dissipated sufficiently and the reason cannot be eliminatedthe extremely large increase of temperature might lead to a fire condition that endangers the surrounding.

If the devices work on the basis of the induction concept engines, dynamos, transformers, relays, etc.

What is the relationship between oxygen and fire

Due to the eddy currents, the structural units coils and their iron cores might warm up, which might lead to the ignition of insulating materials and the burning of the equipment.

Electrostatic sparks Electrostatic charging is a process in the course of which any material, originally with electric neutrality and independent of any electric circuit becomes charged positively or negatively. This may occur in one of three ways: These three ways of charging may arise from various physical processes, including separation after contact, splitting, cutting, pulverizing, moving, rubbing, flowing of powders and fluids in pipe, hitting, change of pressure, change of state, photoionization, heat ionization, electrostatical distribution or high-voltage discharge.

Electrostatic charging may occur both on conducting bodies and insulating bodies as a result of any of the processes mentioned above, but in most cases the mechanical processes are responsible for the accumulation of the unwanted charges.

From the large number of the harmful effects and risks due to electrostatic charging and the spark discharge resulting from it, two risks can be mentioned in particular: Electronic equipment is endangered first of all if the discharge energy from the charging is sufficiently high to cause destruction of the input of any semi-conductive part. The development of electronic units in the last decade has been followed by the rapid increase of this risk. The development of fire or explosion risk necessitates the coincidence in space and time of two conditions: This hazard occurs mainly in the chemical industry.

It may be estimated on the basis of the so-called spark sensitivity of hazardous materials minimum ignition energy and depends on the extent of charging. It is an essential task to reduce these risks, namely, the large variety of consequences that extend from technological troubles to catastrophes with fatal accidents. There are two means of protecting against the consequences of electrostatic charging: Lightning is an atmospherical electric phenomenon in nature and may be considered an ignition source.

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The static charging produced in the clouds is equalized towards the earth lightning stroke and is accompanied by a high-energy discharge. The combustible materials at the place of lightning stroke and its surroundings might ignite and burn off.

At some strokes of lightning, very strong impulses are generated, and the energy is equalized in several steps. In other cases, long-lasting currents start to flow, sometimes reaching the order of magnitude of 10 A. Mechanical heat energy Technical practice is steadily coupled with friction. During mechanical operation, frictional heat is developed, and if heat loss is restricted to such an extent that heat accumulates in the system, its temperature may increase to a value that is dangerous for the environment, and fire may occur.

Friction sparks normally occur at metal technological operations because of heavy friction grinding, chipping, cutting, hitting or because of metal objects or tools dropping or falling on to a hard floor or during grinding operations because of metal contaminations within the material under grinding impact. It has been proven in practice that friction sparks mean real fire risk in air spaces where combustible gases, vapours and dusts are present in dangerous concentrations.

Thus, under these circumstances the use of materials that easily produce sparks, as well as processes with mechanical sparking, should be avoided. In these cases, safety is provided by tools that do not spark, i. Hot surfaces In practice, the surfaces of equipment and devices may warm up to a dangerous extent either normally or due to malfunction. Ovens, furnaces, drying devices, waste-gas outlets, vapour pipes, etc. Furthermore, their hot surfaces may ignite combustible materials coming close to them or by coming in contact.

For prevention, safe distances should be observed, and regular supervision and maintenance will reduce the probability of the occurrence of dangerous overheating.

Fire Hazards of Materials and Products The presence of combustible material in combustible systems represents an obvious condition of burning. Burning phenomena and the phases of the burning process fundamentally depend on the physical and chemical properties of the material involved.

Therefore, it seems reasonable to make a survey of the flammability of the various materials and products with respect to their character and properties. For this section, the ordering principle for the grouping of materials is governed by technical aspects rather than by theoretical conceptions NFPA Wood and wood-based products Wood is one of the most common materials in the human milieu. Houses, building structures, furniture and consumer goods are made of wood, and it is also widely used for products such as paper as well as in the chemical industry.

Wood and wood products are combustible, and when in contact with high-temperature surfaces and exposed to heat radiation, open flames or any other ignition source, will carbonize, glow, ignite or burn, depending upon the condition of combustion.

To widen the field of their application, the improvement of their combustion properties is required. In order to make structural units produced from wood less combustible, they are typically treated with fire-retardant agents e. The most essential characteristic of combustibility of the various kinds of wood is the ignition temperature. It is interesting to note that the ignition temperature as determined by various test methods differs.

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Experience has shown that the inclination of clean and dry wood products to ignition is extremely low, but several fire cases caused by spontaneous ignition have been known to occur from storing dusty and oily waste wood in rooms with imperfect ventilation. It has been proven empirically that higher moisture content increases the ignition temperature and reduces the burning speed of wood.

The thermal decomposition of wood is a complicated process, but its phases may clearly be observed as follows: In this temperature range, sustaining combustion has already developed. After ignition, burning is not steady in time because of the good heat-insulating ability of its carbonized layers. Consequently, the warming up of the deeper layers is limited and time consuming. When the surfacing of the combustible decomposition products is accelerated, burning will be complete.

During its additional glowing, ash containing solid, inorganic materials is produced, and the process has come to an end.

  • Home oxygen and domestic fires

Fibres and textiles The majority of the textiles produced from fibrous materials that are found in the close surrounding of people is combustible. Clothing, furniture and the built environment partly or totally consists of textiles. The hazard which they present exists during their production, processing and storing as well as during their wearing. The basic materials of textiles are both natural and artificial; synthetic fibres are used either alone or mixed with natural fibres.

The chemical composition of the natural fibres of plant origin cotton, hemp, jute, flax is cellulose, which is combustible, and these fibres have a relatively high ignition temperature approx. It is an advantageous feature of their burning that when brought to high temperature they carbonize but do not melt. This is especially advantageous for the medical treatments of burn casualties. The plastics industry, utilizing several extremely good mechanical properties of polymer products, has also gained prominence in the textile industry.

Among the properties of acrylic, polyester and the thermoplastic synthetic fibres nylon, polypropylene, polyethylenethose associated with burning are the least advantageous.

Most of them, in spite of their high ignition temperature approx.

relationship between oxygen and fire hazard

These burning properties may be improved by addition of natural fibres, producing so-called textiles with mixed fibres. Further treatment is accomplished with flame-retardant agents.

For the manufacture of textiles for industrial purposes and heat-protective clothing, inorganic, non-combustible fibre products including glass and metal fibres are already used in large quantities. The most important fire hazard characteristics of textiles are the properties connected with ignitability, flame spread, heat generation and the toxic combustion products. Special testing methods have been developed for their determination. The test results obtained influence the fields of application for these products tents and flats, furniture, vehicle upholstery, clothes, carpets, curtains, special protective clothing against heat and weatheras well as the stipulations to restrict the risks in their use.

relationship between oxygen and fire hazard

An essential task of industrial researchers is to develop textiles that sustain high temperature, treated with fire-retardant agents, heavily combustible, with long ignition time, low flame spread rate, low speed of heat release and produce small amounts of toxic combustion products, as well as to improve the unfavourable effect of fire accidents due to the burning of such materials.

Combustible and flammable liquids In the presence of ignition sources, combustible and flammable liquids are potential sources of risk. First, the closed or open vapour space above such liquids provides a fire and explosion hazard.

Combustion, and more frequently explosion, might occur if the material is present in the vapour-air mixture in suitable concentration. From this it follows that burning and explosion in the zone of combustible and flammable liquids may be prevented if: These are closed-cup and open-cup flash points, boiling point, ignition temperature, rate of evaporation, upper and lower limits of the concentration for combustibility flammable or explosive limitsthe relative density of vapours compared to air and energy required for the ignition of vapours.

These factors provide full information about the sensitivity for ignition of various liquids. Nearly all over the world the flash point, a parameter determined by standard test under atmospherical conditions, is used as the basis to group the liquids and materials behaving as liquids at relatively low temperatures into categories of risk. The safety requirements for storage of liquids, their handling, the technological processes, and the electrical equipment to be set up in their zone should be elaborated for each category of flammability and combustibility.

The zones of risk around the technological equipment should also be identified for each category. In respect to fire and explosion hazards, gases may be ranked in two main groups: According to the definition accepted in practice, combustible gases are those that burn in air with normal oxygen concentration, provided that the conditions required for burning exist. Ignition only occurs above a certain temperature, with the necessary ignition temperature, and within a given range of concentration.

Non-combustible gases are those that do not burn either in oxygen or in air with any concentration of air. A portion of these gases support combustion e.

The non-combustible gases not supporting burning are called inert gases nitrogen, noble gases, carbon dioxide, etc. Air is mostly nitrogen, which is not flammable. Nitrogen is also non-reactive in general, so it doesn't support the combustion of other materials, either.

After nitrogen, the most abundant gas in our air is oxygen. Here's where it gets complicated: Oxygen is also not flammable, but it is a high-energy gas that very readily oxidizes other materials.

relationship between oxygen and fire hazard

For something to burn, the reaction requires a fuel the thing that burns and an oxidizer like oxygen. Without the fuel, though, no combustion will take place no matter how high the concentration of oxygen is.

Since air itself is not flammable, it is not a fuel and will not combust, spontaneously or otherwise. The danger we often hear about with high oxygen levels is that other materials that are not combustible or only very slightly combustible under normal conditions, and therefore not a danger, can become very combustible and hazardous when oxygen levels are high.

Also, many things will be hot or will smolder when deprived of air and thus oxygenand will suddenly burst into flame when exposed to the oxygen that's in our air. Examples of this include oily rags in a trash can that ignite when someone lifts off the can's lid, or toast in a toaster oven that is black and smoky and that bursts into flame when someone opens the oven door. Since oxygen is required for the burning we see, the sudden combustion in these examples would be more dangerous if the oxygen concentration were higher.

One final thing to note is the difference between combustion and spontaneous combustion.