See also: decipol.

A unit describing the rate at which odor is added to air, based on human perception of odor. One olf is the rate at which 1 human adult, who is wearing deodorant but not perfume, takes 0.7 baths per day, changes his or her underwear every day, and is resting at a comfortable air temperature, emits air pollutants (which the researchers call “bioeffluents”, and most of us, “body odor”). The olf is used in designing ventilation systems to reach specified levels of perceived air quality.

Use of the olf is not restricted to people as sources. The rate at which all sorts of sources, from carpeting to photocopiers, emit air pollutants, can be described in olfs. The sum of all the non-living sources in an office building is commonly described in olfs per square meter.

The unit was introduced¹ in 1988 by the distinguished Danish indoor air quality researcher Povl Ole Fanger (1934 –2006). Previous work on indoor air quality had concentrated on chemical analysis of pollutants. However, people complained of poor indoor air quality when the pollutants were at levels too low to measure by the existing technology. Fanger et al turned to using people as his instrumentation. At least 20 naive judges would individually enter an air space with a measured rate of ventilation and a measured rate of human bioeffluents emission, and decide whether the air quality was satisfactory or unsatisfactory.

From hundreds of such experiments Fanger was able to construct a curve graphing the percent dissatisfied against the ventilation rate in liters per second per olf. The usefulness of the curve is that it predicts what ventilation rate will be needed for any combination of olfs and acceptable level of dissatisfaction.

Fanger's graph

After Fanger (1988)

The graph shows that, for example, if we can live with 30% of the employees dissatisfied with the office air quality, a ventilation rate of slightly less than 5 liters per second per olf will suffice.

To determine whether the curve reflected peculiarly European sensibilities, other researchers did similar tests in the United States and Japan, with similar results.

The olf has been used in publications of the European Committee for Standardization (CEN) and in government building codes (for example, Norway).

Source Sensory Load
in olfs
Sedentary person (1 - 1.5 met) 1
Person exercising (3 met) 4
Person exercising (6 met) 10
Children, 3 - 6 years 1.2
Children, 4 - 16 years 1.3
Building, low pollution
per square meter
Building, polluting,
per square meter
Smoker (while not smoking) 6

1. P. O. Fanger.
Introduction of the olf and decipol units to quantify air pollution perceived by humans indoors and outdoors.
Energy and Buildings, vol. 12, pages 1-6 (1988).

P. O. Fanger, J. Lauridsen, P. Bluyssen and G. Clausen.
Air pollution sources in offices and assembly halls quantified by the olf unit.
Energy and Buildings, vol. 12, pages 7-19 (1988).

Ventilation for Buildings: Design criteria for the indoor environment.
Technical Report CR1752.
Brussels: European Committee for Standardization, 1998.

[Norwegian Building Code.]
Oslo: Statens Hygningstekniske Eur., 1996.

for further reading

American Society of Heating, Refrigerating and Air-conditioning Engineers.
2009 ASHRAE Handbook. Fundamentals (SI).
Atlanta, GA: American Society of Heating, Refrigerating and Air-conditioning Engineers, 2009.

Chapter 12, specifically page 12.6.


The idea is to express any pollution source by a comparable known reference source. The new unit is called one “olf”, from the latin word olfactus (olfaction), although both the olfactory and chemical sense are involved in the definition of the unit. One olf is the emission rate of air pollutants (bioeffluents) from a standard person. Any other pollution source is then expressed by the equivalent source strength, defined as the number of standard persons (olfs) required to cause the same dissatisfaction as the actual polution source. The olf is thus a relative unit similar to the met unit for metabolic rate or the clo unit for insulation of clothing, both introduced by Gagge et al.

P. O. Fanger, Energy and Buildings, vol. 12, 1988, page 2.

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