What are Volatile Organic Compound (VOC) gases?

Volatile organic compound (VOC) gases include a wide range of both natural and synthetic substances. VOCs are chemical compounds – mixtures of more than one element – where one of the elements is carbon. They are described as volatile because they evaporate easily, releasing molecules into the atmosphere.

In some places, notably California (and previously in the USA as a whole), VOCs are known as ROGs or reactive organic gases. This focuses attention on the more important reactive gases, but the distinction causes some confusion and the term VOC is generally preferred. In French, VOCs are known as COV.

Some common gases such as carbon dioxide CO2, carbon monoxide CO, and carbonic acid, are not included in the classification as VOCs because they are not particularly reactive or volatile.

Where are volatile organic compound (VOC) gases found?

VOC gases are present in everyday life and can be harmless, some however, are not and can be hazardous to health and the environment. Solvents used in paints and adhesives, and in cleaning products, are often VOCs. The distinctive smell of some new plastics is the result of the ‘outgassing’ or release of volatile organic compound gases into the atmosphere. Fuels including diesel, petrol, gasoline, heating oil, and aviation fuel are VOCs.

These and other potentially hazardous volatile organic compound gases including benzene, toluene, ethylene, xylene, and formaldehyde require careful monitoring by an appropriate gas detection instrument or sensor. The legal limits on emissions of and exposure to VOC gases vary from place to place, and are set by authorities including the Health & Safety Executive EH40/2005 ‘Workplace exposure limits’ and the Occupational Safety and Health Administration OSHA. One common definition of a VOC, which has been adopted by the EU, World Health Organisation WHO, and others including Health Canada, is a carbon compound with a boiling point below 25^oC.

Harmful VOC gases are produced and released to the environment by many human activities, including transportation, manufacturing, printing, and agriculture. They are also produced naturally by plants, but these VOCs are generally harmless.

Hazards to health and the environment

The hazards presented by VOC gases fall into a number of categories. The most volatile substances, sometimes referred to as very volatile organic compounds or VOCs, may present a risk of fire or explosion. Some VOCs including methylene chloride (found in paint strippers and aerosol paints), benzene, and perchloroethylene (dry cleaning fluid) are hazardous to human and animal health or may cause cancer (carcinogenic).

Other VOCs may be serious pollutants, either by directly contaminating the environment or by reacting with sunlight and other gases in the atmosphere – known as photoreactivity – to generate photochemical smog.

When considering VOCs, a distinction may be made between their effect on the outdoor environment and on indoor air quality. Concentrations indoors will often be much higher than outdoors, and VOCs from sources including faulty air conditioning and office equipment are implicated in ‘sick building syndrome’.