Standards for Indoor Air Quality (IAQ)

There are several rating systems for indoor air quality and how the indoor air quality can be determined from measuring TVOC concentrations.

Indoor Air Quality Levels by German Federal Environmental Agency

Following the human perception, the German Federal Environmental Agency translates TVOC concentration (parts per billion) on a logarithmic scale into five indoor air quality levels (IAQ), as shown in Table below.

Level Hygienic Rating Recommendation Exposure Limit TVOC [ppm]
Unhealty Situation not acceptable Use only if unavoidable /
Intense ventilation necessary
hours 2.2 - 5.5
Poor Major objections Intensified ventilation / airing necessary
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< 1 month 0.66 - 2.2
Moderate Some objections Intensified ventilation / airing recommended
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< 12 months 0.22 - 0.66
Good No relevant objections Ventilation / airing recommended no limit 0.065 - 0.22
Excellent No objections Target value no limit 0 - 0.065

Bundesgesundheitsblatt – Gesundheitsforschung Gesundheitsschutz 2007, 50:990–1005, Springer Medizin Verlag 2007. (DOI 10.1007/s00103-007-0290-y)

Thereby the five stages or so called IAQ levels extend from Level 1 (excellent) to Level 5 (unhealthy). Extended exposure to increased IAQ levels, i.e. to bad air, can affect the comfort, well-being and health of building occupants. Poor indoor air quality is linked e.g. to sick building syndrome, reduced productivity and impaired learning in schools.

Air Quality Guidelines by the World Health Organization (WHO)

The World Health Organization (WHO) released indoor air quality guidelines for Europe which are classified by means of TVOC concentration values. Different air quality classes and their corresponding class limits in TVOC concentration are listed in Table below.

Level Recommendation TVOC [mg/m³] TVOC [ppm]
Outside quality classes Greatly increased
(not acceptable)
> 3.0 > 0.61
4 Significantly increased
(only temporary exposure)
1.0 - 3.0 0.20 - 0.61
3 Slightly increased
(harmless)
0.5 - 1.0 0.10 - 0.20
1 Target value > 0.25 0 - 0.05

Air quality guidelines for Europe – Second Edition; hg. v. World Health Organization – WHO, Copenhagen (2000).

Directive for the assessment of the indoor air, published by the working group on indoor air in the Ministry of Sustainability and Tourism (BMNT) and the Commission for Clean Air of the Austrian Academy of Sciences (KRL). Vienna (2014).

RESET Standard for Indoor Air Quality

RESET Air for Commercial Interiors is a continuous monitoring and communication standard for indoor air quality with the goal of raising public awareness of indoor air quality and its impacts on environmental aspects and occupant health. Goal of the standard is continuous monitoring of particulate matter (PM2.5), TVOC and CO2 concentrations. Since long-term exposure to VOCs can cause damage to the liver, kidneys and the central nervous system, the RESET standard formulates IAQ performance targets for an average daily exposure to TVOC concentrations, as listed in Table below.

TVOC concentration regarding RESET target [µg/m³] [ppm]
Acceptable < 500 < 0.25
High Performance < 400 < 0.2

RESET™ Air Standard for Commercial Interiors v2.0, 2018

Translation from mass concentration [µg/m³] to particle concentration [ppb] is based on an average molar mass of TVOC molecules, according to the TVOC mix proposed by Mølhave (Ref.: Mølhave L, Clausen G, Berglund B, et al. (1997) Total Volatile Organic Compounds (TVOC) in Indoor Air Quality Investigations. Indoor Air 7:225-240). Thereby 4.9 µg/m³ corresponds to 1 ppb TVOC concentration.

LEED Green Building Rating System

LEED, or Leadership in Energy and Environmental Design, is the most widely used green building rating system. It aims for providing a framework to create healthy, highly efficient and cost-saving green buildings by providing globally recognized certifications. The LEED scoring function was developed based on the LEED TVOC limit of 500 µg/m³, as shown in Table below.

Green building standard LEED [µg/m³] [ppm]
TVOC limit < 500 < 0.25

What is Air Quality Score (AQS)?