Carbon monoxide flammability limits

Table 6. Flammability Limits of Carbon Monoxide in Dry Air as a Function of Temperature at Atmospheric Pressure ...

Fire Hazards - Flash Point Not flammable Flammable Limits in Air (%) Not flammable Fire Extinguishing Agents Not pertinent Fire Extinguishing Agents Not To Be Used Not pertinent Special Hazards of Combustion Products Toxic carbon monoxide gas may form in fire Behavior in Fire Not pertinent Ignition Temperature Not pertinent Electrical Hazard Not pertinent Burning Rate Not pertinent. 

Below atmospheric pressure there is no effect on the limits of flammability of natural gas-air mixtures and most other gas-air mixtures. Below about 25 mm absolute pressure, carbon monoxide-air mixtures are not flammable. 

Figure 14. Flammable limits for hydrogen, carbon monoxide, methane, with nitrogen, carbon dioxide and water vapor.

Carbon monoxide is a highly flammable and poisonous gas. Its flammable limits in air are 12.5 to 74.2% by volume, and the autoignition temperature 700°C. It explodes when exposed to flame. Reactions with interhalogen compounds, such as, bromine pentafluoride or halogen oxides can cause explosion. It forms explosive products with sodium or potassium that are sensitive to heat and shock. 

The presence of the catalyst provides a lower-energy chemical path than that offered by a thermal reaction. A catalyst accelerates oxidation of hydrocarbon/carbon monoxide/air mixtures that lie outside the flammability range required for thermal reactions. In the exhaust of the automobile the composition of the pollutants is far below the flammability range yet the oxidation reactions occur by the catalyst providing a lower-energy chemical path to that offered by the thermal reaction. An excellent example is the oxidation of CO with and without a catalyst. Without a catalyst the rate-limiting step is 02 dissociation at 700°C followed by reaction with gas phase CO. In the presence of the Pt catalyst 02 dissociation is rapid and the rate-limiting step becomes the surface reaction between adsorbed O atoms and CO that occurs below 100°C. 

Hazard Highly flammable, dangerous fire and explosion risk. Flammable limits in air 12-75% by volume. Toxic by inhalation. TLV 25 ppm. Note Carbon monoxide has an affinity for blood hemoglobin over 200 times that of oxygen. A major air pollutant. 

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