Flammability diagram methane - purge commissioning

The limiting oxygen concentration (LOC), also known as the minimum oxygen concentration (MOC), is defined as the limiting concentration of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

below which

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

is not possible, independent of the concentration of fuel. It is expressed in units of volume percent of oxygen. The LOC varies with pressure and temperature. It is also dependent on the type of inert (non-flammable) gas. Limiting oxygen concentration for solid materials The effect of increasing the concentration of

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

can be understood by viewing the inert as thermal ballast that quenches the flame temperature to a level below which the flame cannot exist. Carbon dioxide is therefore more effective than nitrogen due to its higher molar

heat capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat capacity ...

.Drysdale:92 The concept has important practical use in fire safety engineering. For instance, to safely fill a new container or a pressure vessel with flammable gasses, the atmosphere of normal air (containing 20.9 volume percent of oxygen) in the vessel would first be flushed (purged) with

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

or another

non-flammable A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

inert gas, thereby reducing the oxygen concentration inside the container. When the oxygen concentration is below the LOC, flammable gas can then be safely admitted to the vessel, because the possibility of internal explosion has been eliminated. The limiting oxygen concentration is a necessary parameter when designing

hypoxic air fire prevention system Hypoxic air technology for fire prevention, also known as oxygen reduction system (ORS), is an active fire protection technique based on a permanent reduction of the oxygen concentration in the protected rooms. Unlike traditional fire suppression ...

Sources

Monographs * ''Chapter 23'' * * ''(Presented at 9th International Symposium on Loss Prevention and Safety Promotion in the Process Industries, May 1998, Barcelona (Spain))''

References

{{reflist Combustion Explosion protection Fire Safety

See also

Sources

References