Volatile Organic Compounds (VOCs) and Air Quality
What are VOCs
VOCs are commonly associated with solvents. Solvents are intended to be volatile, meaning they evaporate quickly. Most VOC of concern are emitted from solids and liquids. VOCs are defined as organic chemical compounds whose composition makes it possible for them to evaporate under normal indoor atmospheric conditions of temperature and pressure. VOCs are a significant risk for pulmonary disease, neurological disorders, and cancer.
Understanding VOC Levels
Currently, there are no statutory limits at the Federal level in the USA. ASHAE Addendum 62-2001 describes the difficulty of establishing an overall standard for such a diverse group of compounds. Form Table B-2 of 62-2001: “no single method currently in use measures all organic compounds that may be of interest. Therefore, some inves- tigators have reported the total of all measured VOCs as the Total of VOCs in order to make explicit that the reported value does not represent the total of all VOCs present.” . The WELL building standard specifies VOC levels of Formaldehyde levels less than 27 ppb and Total Volatile Organic Compounds less than 500 μg/m³.
Sources of Potential Exposure
Paints, paint strippers, coatings, and thinners
Wood preservatives and resins.
Aerosol sprays
Cleansers and disinfectants
Moth repellents
Air fresheners
Stored fuels and automotive cleaners and additives
hobby supplies
Health Hazards
Eye, nose and throat irritation
Headaches, loss of coordination and nausea
Damage to liver, kidney and central nervous system
Difficulty breathing
Nosebleeds
Nausea
Fatigue
Dizziness
Measuring VOCs
WellStat devices use two independent sensors for VOCs, one is specifically calibrated for Formaldehyde, and the other is a broad spectrum sensor called a “Total” VOC sensor, or TVOC sensor. Both sensors are an Electrochemical (EC) type. Wellstat devices use two different types because TVOC sensors are not normally calibrated to substances of interest in buildings. The TVOC sensor used in WellStat is manufactured with a response curve for Methanol and Acetone, and is calibrated at the factory using Isobutylene. The TVOC sensor used in WellStat has a broad response range, up to 10ppm but its accuracy is not specified at low concentrations needed for detecting low background levels. The WellStat Formaldehyde sensor gives excellent accuracy at low levels, up to 2000ppb. The WellStat TVOC sensor is well suited for detecting intermittent events of high concentrations, such as spills, which would blind other sensors of lower range.
Conversion of Units
The conversion of WellStat VOC readings between mass density and ppm units is recommended for Formaldehyde. TVOC readings are by definition broad spectrum and the unit conversion by definition requires the molar mass of the substance. The unit conversion equation is as follows:
Concentration (ug/m3) = 0.0409 x concentration (ppb) x molecular weight
Concentration (ppb) = 24.45 x concentration (ug/m3)÷ molecular weight
Example:
The WellStat Formaldehyde sensor reports that the concentration is 25ppb. What is the concentration in ug/m3?
The chemical formula for Formaldehyde is CH2O. The molecular weight is 30.03g/mol.
Concentration = 0.0409 x 25 x 30.03 = 31 ug/m3