Gases can be classified into three groups: oxidizers, inert gases and flammable gases. Oxidizers, such as oxygen and chlorine, are not flammable on their own but will act as an oxidant and aid combustion. Inert gases are not combustible at all, and are sometimes used in fire suppression systems. Carbon dioxide and helium are examples of inert gases. Flammable gases can be explosive when mixed with air in the right proportions. Hydrogen, butane, methane and ethylene are examples of flammable gases.
Hydrogen is the most basic of all the known elements. Its name comes from the Greek words meaning water-forming. Hydrogen was produced in the lab as far back at 1671—before it was understood to be an element. Hydrogen is used as a fuel by stars, powering the nuclear reactions that allow them to burn for billions of years. It is highly combustive when mixed with oxygen. Hydrogen is present in many common compounds encountered everyday. Water, hydrogen peroxide and even table sugar are made from hydrogen.
The term butane can refer to the alkane n-butane or to its other isomer, isobutane. Both gases are colorless, odorless, easy to liquify and extremely flammable. Butane gas is used for camping and cooking fuel. Butane is sometimes blended with propane and sold commercially, where It is used as cigarette lighter fuel or aerosol propellant. Butane in its purest form is sometimes used as a coolant, being a more environmentally friendly alternative to the ozone-depleting coolants once common in refrigerators.
Methane, often sold under the name natural gas, is used primarily as a residential and commercial heating fuel. Because methane is explosive when present in the air, leaks of natural gas are dangerous. In its natural state methane has no color or odor, so gas companies add an unpleasant sulfurous smell, making gas leaks easy to detect. In nature, methane is found in underground reservoirs often with deposits of petroleum. Methane is generally processed before being sold to remove propane, butane and other impurities, some of which are sold separately.
Ethylene is a colorless, odorless gas, primarily produced by plants, though also manufactured artificially. Ethylene is known as the ripening hormone for fruits, flowers and vegetables. Placing produce in a paper bag causes the ethylene levels in the bag to rise because the fruit or vegetable itself is producing the gas. The presence of ethylene will accelerate the ripening process. The same effect occurs in other closed spaces, such as fruit trucks and warehouses. Ethylene is flammable when the air contains a 13 to 32 percent concentration of the gas.
Other Flammable Gases
There are many other gases that can become flammable when mixed with air or oxygen, including acetylene, ammonia, ethane, propane and silane. Some of these gases are used commercially for grills or to heat homes. When using a flammable gas, always be aware of the properties of the specific gas you are using, for example the level of ventilation needed when burning the gas and whether it will float and collect near your ceiling or sink to your floor.