What is a volatile organic compound (VOC)?
Volatile organic compounds (VOCs) 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. VOCs can be detected by specialised VOC detectors utilising photoionsation detection (PID) technology.
VOCs 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 compounds to the atmosphere. Fuels including diesel, petrol, gasoline, heating oil, and aviation fuel are VOCs.
These and other potentially hazardous volatile organic compounds including benzene, toluene, ethylene, xylene, and formaldehyde require careful monitoring. The legal limits on emissions of and exposure to VOCs vary from place to place, and are set by authorities including the European Union and the United States 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 250C.
Harmful VOCs 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.
VOCs play a vital part in many industrial processes and products. Factories and other places where VOCs are routinely present will monitor their environment and surroundings by using fixed VOC detectors. These instruments are permanently installed and provide continuous measurement of volatile organic compounds in the air they sample.
A handheld VOC detector, which is a lightweight portable instrument, may be used in conjunction with a fixed VOC detector to provide spot measurements. Small, lightweight VOC detectors may be attached to clothing as part of the personal protective equipment issued to workers.
Handheld VOC detectors are used to locate and measure VOCs in any place where they might be present, either indoors or outdoors. This may be as the result of a spill, machinery breakdown, or other unexpected event. A handheld VOC detector is useful for checking confined spaces such as inside pipework and sewers, in industrial safety and hygiene, and in decontamination monitoring.
The hazards presented by VOCs fall into a number of categories. The most volatile substances, sometimes referred to as very volatile organic compounds or VVOCs, 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’.
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.