Stability of body odor in enclosed spaces

Environment International, Vol. 12, pp. 201-205, 1986

0160-4120/86 $3.00 + .00 Copyright © 1986 Pergamon Journals Ltd.

Printed in the USA. All rights reserved.

STABILITY OF BODY ODOR IN ENCLOSED SPACES G. H. Clausen and P. O. Fanger Laboratory of Heating and Air Conditioning, Technical Universityof Denmark, DK2800, Lyngby, Denmark

W. S. Cain and B. P. Leaderer John B. Pierce Foundation Laboratory, Yale University, New Haven, Connecticut 06519, USA (Received 26 February 1985; Accepted 13 September 1985)

Sedentary subjects occupied an environmentalchamber (20-22 °C, 35%-50% RH) with low ventilation for 90 min. Judges (visitors) evaluated the odor of the chamber before, during, and after the 90-min period of occupancy. Odor intensity increased throughout occupancyand decayed afterwards. However, the rate of decay exceededthat anticipated from ventilationrate alone. The results implied that body odor is unstable with a half-life of 55 rain. This instability will influence quantitative requirements for the ventilation during nonsmoking occupancy.

peared on its own in a matter o f minutes (Fig. 1). Hence, the mere passage o f time had an effect equivalent to actual ventilation. Later studies on required ventilation by Cain et al. (1983) and Fanger and Berg-Munch (1983) implied that body odor might be rather stable with a half-life in the order o f one-half hour or more. But in both these studies experimental sessions were rather brief and not designed to examine stability. In fact, the estimate of half-life (35 min) in Cain's study came from measurements o f the growth o f odor rather than from decay p e r se. An estimate o f 51 min in Fanger and Berg-Munch's study came from measurements of the decay o f initially rather weak odors where precise specification is difficult. In view o f the apparent disparity between Yaglou's study and more recent studies, it seemed worthwhile to re-examine the stability o f body odor in an experiment designed specifically for this purpose.

Introduction

This report deals with the stability o f body odor, a major contaminant in most auditoriums, theaters, meeting rooms, and similar crowded spaces. An odor is stable if it does not change with time, and it is unstable if its intensity decreases with time, e.g., caused by oxidization or adsorption on surfaces. Such instability m a y be quantified by the half-life o f the odor intensity. Body odor originates from sweat and sebaceous secretions from the skin, breath, and gases from the digestive tract. The odor derives from a mixture o f primarily organic gases at low concentrations, not readily measurable. B o d y odor emissions exhibit large individual differences and depend on such factors as diet, activity, and personal hygiene. Yaglou e t al. (1936) concluded that, under steadystate conditions, ventilation requirements for control o f body odor decrease with increasing space (volume) per person. For instance, the ventilation rate per occupant necessary to maintain body odor at a moderate level equalled 3 L/sec when the volume per occupant equalled 13 m 3 and 8 L/sec when the volume equalled 6 m 3 per occupant. Yaglou and Witheridge (1937) suggested that the volume dependence m a y have arisen from instability o f body odor. Their psychophysical measurements indicated that the odor virtually disap-

Theoretical Tools

The concentration C(t) o f a contaminant in an enclosed space with the volume V can be predicted at any given time t from the general mass-balance equation used by Turk (1963), Leaderer et al. (1984), and others. In its most general form, it states: 201

G . H . Clausen et al.

202

Overpowering

coming air equal to zero (C, = 0), Eq. (1) can be reduced to"

Body Odor Very Strong

C ( t ) = Coe-(". + 4--

"~ C

Strong

(4)

Equation (4) represents the case where the contaminant decays towards zero.

C

qD

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Moderate

o

Facilities

Definite ~

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t

Threshold No Odor 0

I

IOO

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200

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300

400

500

6OO

Time o f f e r End of OceupQncy (rain)

Fig. 1. Decay of occupancy odor assessed by judges after occupants vacated Yaglou's environmental chamber. Data from Yaglou and Witheridge (1937).

C ( t ) = Coe-

9(Q. + Q. + eQ,)t

+

mC, Q, + G

re(Q, + Q. + (l

EQ,)

-e--~'Q'+ Q"+ eQ'") ,

(0

where C(t) is the concentration o f the contaminant at a given time t, Co is the concentration o f the contaminant at t = 0, Cv is the concentration o f contaminant in the incoming air, rn is a mixing factor describing the ratio o f actual ventilation to theoretical ventilation with complete instantaneous mixing, Q, is ventilation rate, Qo is equivalent volume removal rate by reaction, adsorption on surfaces, or absorption, Qr is recirculation rate, E is efficiency o f any air cleaning device through which recirculating air passes, and G is contaminant source emission rate (continuous source). In the case where there is no air filter (E = 0), complete and instantaneous mixing (m = 1), and when the concentration o f the contaminant in the incoming air ( C ) and in the space at t = 0 (Co) are both equal zero, the equation can be reduced to:

The tests took place in an aluminum-lined environmental chamber shown schematically in Fig. 2. The chamber had a total air volume, including ducts, o f 34 m 3. The entire floor (11 m 2) served as a diffuser. Air entered via a plenum beneath the floor, streamed upward through 13,900 perforations, and left the chamber via four return ducts. Recirculation kept the atmosphere well mixed. An outside sniffing box of 0.11 m 3 through which passed a portion o f air from the chamber allowed subjects to evaluate the quality of the air in the chamber without entering it. A Dravnieks binary dilution olfactometer ( A S T M , 1981) which emitted eight concentrations ( 1 6 - 2 0 4 8 ~L/L) o f the standard matching odor 1-butanol sat on a surface about 3 m from the sniffing box. This olfactometer served as a sensory yardstick, as described below. Air infiltration was determined by decay o f carbon dioxide injected into the chamber. A Beckman L B 2 Infrared Analyzer monitored the decay. These measurements took place separately from the psychophysical tests. During the tests, the Beckman L B 2 was used to monitor the carbon dioxide level generated by the occupants in the chamber. Subjects

Seven men and 9 w o m e n (23 to 68 yr) served as occupants in the chamber on one or more occasions in ou'rslD( AIR o-nooJ/s

i

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G Q,) (1 - e -(Q'+ Q'~) C( t) = ( Q, +

(2)

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By introducing the air change n as n, = Q,I v and n. = Q, IV, Eq. (2) becomes: G C(t) = (n, + n,) -(lv - e - ( " + ")')'

(3)

CHAMBER COOLING COIL

STEAM HEAT

HEAT

Equation (3) represents the case where a contaminant in a space builds to an equilibrium level over time. In the case of no air filter (E = 0), complete instantaneous mixing (m = 1), no generation o f contaminants ( G = 0), and concentration o f contaminants in the in-

DAMPER

.4---f--4- 4---

H~IIOflER

VENTILATION CHAMOER

Fig. 2. Schematic view of the environmental chamber (shown in crosssection at right) and control equipment. Arrows in the cross-section of the chamber depict the flow of air from floor to ceiling.

Body odor in enclosed spaces

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humidity 3 5 % - 5 0 % . Assessments took about 1 min per judge. Each o f the four test sessions comprised a 30-min pre-occupancy segment, a 90-min occupancy segment, and a 100-rain post-occupancy period. Four control sessions, where occupancy began at 30 min and continued for 190 min, were also performed. The test and control sessions were performed in random order without the judges knowing the nature of each test. During the occupancy period the air was recirculated at a rate o f 100 h -1 to insure proper mixing in the chamber. Leakage in the ducts, doors, and air handling systems led to a fresh air change of 1.36 hunder those conditions. A recirculation rate o f 25 hresulted in an air change o f 0.46 h -~ before and after occupancy.

I

30

I

60

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120 Time

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180

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I

240

(min)

Fig. 3. Odor intensity expressed as butanol concentrations, as a function of time for both test and control sessions. Each point on the graph is the geometric m e a n of 70-90 evaluations made over a 20-rain segment.

groups o f eight at a time. These persons generated odor by their occupancy and made no odor judgments. Twenty-four w o m e n (22 to 65 yr) participated as odor judges.

Procedure Before the tests, the judges were familiarized with the sniffing box and with the use o f the olfactometer in a 2-h introductory session. During a test, groups of 8 to 16 judges evaluated the odor intensity in the chamber. The judges occupied a well-ventilated waiting room 25 m from the sniffing station. They were kept naive with respect to whether or not the chamber was occupied. The judges walked serially from the waiting room to the sniffing station. Immediately after sniffing the air, the judge rated odor intensity on a graphic scale that contained the six annotations previously used by Yaglou: no odor, slight odor, moderate odor, strong odor, very strong odor, overpowering odor. This assessment served to capture the immediate impression o f odor intensity. The judge then chose from the Dravnieks olfactometer a concentration o f the woody-pungent alcohol 1-butanol that matched the odor intensity in the chamber. The level o f butanol chosen from the olfactometer served as the primary psychophysical judgment. The judge also assessed whether or not the odor was acceptable. Air temperature in the chamber was 2 0 - 2 2 °C and relative

Figure 3 depicts the buildup and decay of body odor for test and control conditions. Each data point in the semilog plot is the geometric mean o f approximately 90 evaluations obtained from the use o f the olfactometer during a 20-min interval. Both functions rise in much the same way during the overlapping 90 min of occupancy and, as expected, diverge thereafter. The constant displacement between the functions before and during occupancy has no obvious explanation. However, it is hardly surprising that an odor stimulus specifiable only in terms o f chamber conditions, number o f occupants, ventilation rate, etc., should vary somewhat. Also, the composition o f occupant groups were not identical in the test and control sessions, although the occupants were all from the same base group o f 7 men and 9 women. In any case, the form o f the function, particularly in the decay period, holds the major interest here. Figure 4 depicts the buildup (3) and decay (4) of body odor in the experimental conditions when a background odor level (pre-occupancy judgments) equivalent to 20 IxL/L butanol has been subtracted. If body odor had been stable, the decay would have followed the dashed line corresponding to the air infiltration o f 0.46 h -1. The steeper decay means that body odor was not stable. From linear regression on the post-occupancy data points, the slope of the decay was determined to be - 1.22 h-~ (r = - 0.99). This slope represents - ( n , + n,) in (4). Since n, = 0.46, n= can be calculated as na = (1.22 - 0.46)h -t = 0.76h -~. The time constant for the decomposition o f body odor (the time required for the concentration o f the body odor to reach l/e o f its initial value) is ~" = 1/n,, = 79 rnin. This corresponds to a half-life o f ln2 • ~ = 55 min. There was excellent agreement between odor intensity obtained from the use o f Yaglou's scale and from the use o f the olfactometer. Figure 5 shows the rela-

204

G . H . Clausen et al.

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Intensity

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(ppm

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Butonol)

Fig. 6. Percentage of dissatisfied as a function of odor intensity (equivalent butanol concentration).

(rain)

Fig. 4. Odor intensity expressed as butanol concentration, as a function of time for test sessions. The background odor level o f 20 ~tl.,/L butanol has been subtracted. Acceptalbility equalled 100% at the start of occupancy, fell to 68% at the end of occupancy, and then rose to 100% by the end of the test.

tion between the two modes of evaluation. It can be expressed by the equation:

sity expressed in Yaglou's scale value (0 = no odor, 1 = slight odor, 2 = moderate odor, 3 = strong odor, 4 = very strong odor, 5 = overpowering odor). Figure 6 depicts percent dissatisfaction (i.e., judgments of unacceptable) against the log of odor intensity expressed in terms of equivalent butanol concentration. The straight line indicates a log-normal distribution of percent dissatisfaction.

~8 = 12.8 e ~-ae¢', Discussion

where ~n is the odor intensity expressed in equivalent butanol concentration (p,L/L) and ~ r is the odor inten-

400 300

Odor Intensity

/

200

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70

E

50

Q"

30

•

20 I 10 " 0

i

I 1.0 Yoglou's

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Scole

Fig. 5. Odor intensity in terms of equivalent butanol concentration versus odor intensity expressed in Yaglou's scale values.

The outcome indicated that body odor is much more stable than that measured by Yaglou and Witheridge (1963), and less stable than recent results by Cain et al. (1983) and Fanger and Berg-Munch (1983) would imply. It was not possible in the present study to distinguish between adsorption on surfaces and chemical conversion of body odor as the reason for the decay n~. Adsorption implies an actual reduction in airborne concentration, whereas conversion implies the creation of less odorous constituents. Oxidized products, for instance, commonly have less odor. The high rate of recirculation in the present study may have had some influence on the degree of adsorption. Further studies like the present, but without recirculation, are recommended. Furthermore, field studies in spaces with actual furnishings, but with less recirculation, will help decide the generality of the present estimate of half-life. It will be of particular interest to discover whether the remarkably rapid decay found by Yaglou and Witheridge (1937), but not confirmed by more modern studies, will occur under one set of circumstances or another.

Body odor in enclosed spaces

205

1.0

nv

5.0 h-I o LO

0.5

0.5

~

o O0

i

i

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T i m e o f f e r Start of Occupancy (hours) Fig. 7. Decay ratio as a function of time shown for different air changes n , in the case of constant occupancy beginning at t = 0. (Half-life of body odor equal to 55 min).

The influence of instability can be quantified by introducing the term "stability ratio c~." The stability ratio of a gas is the ratio of actual to theoretical concentration assuming stability. For a perfectly stable contaminant, the stability ratio will equal 1, but for an unstable contaminant, the stability ratio will fall below 1 and will be a function of time and infiltration rate. In the case of constant occupancy beginning at t = 0 (with no odor at the outset) and infiltration rate nv, the stability ratio can be expressed as: n, (1 - e -t". + ".~') ot = (nv + n,)(1 - e-".t)"

decayed rapidly provided at least qualitative confirmation of that conclusion. Yaglou and Witheridge did not estimate an exact decay rate. It is possible, however, to ask what decay would be necessary to produce the anticipated proportionality between number of occupants in a space and ventilation requirements found in the earlier study by Yaglou et al. (1936). A simple, graphical procedure yielded n~ = 2.4 h-1, or a halflife of app. 17 rain. This value of n, is substantially higher than that seen by Yaglou and Witheridge (1937) (under 5 min), but well below that measured here or estimated from the data of Cain et al. (1983) or Fanger and Berg-Munch (1983). Indirect estimates of decay, such as that mentioned above or that computed from the growth curves of Cain et al. (1983), will inevitably suffer from some inaccuracy. Further investigation may enable us to discover whether disparities between the older and newer work represent merely systematic and ultimately predictable variation that derives from how the decay of body odor depends on the materials in a space, rate of recirculation, and environmental factors. Whatever the eventual outcome, the answer has important policy implications for deciding ventilation requirements in places of nonsmoking occupancy. Acknowledgements--Supported by grant ES 00354 from the U.S. Nationai Institutes of Health and by the Department of Energy in Denmark. We thank Mr. Tarik Tosun for technical assistance.

(5)

References Figure 7 depicts the stability ratio for body odor as a function of time for different values of nv given the conditions stated above and assuming a half-life of body odor of 55 min. For steady-state conditions, Eq. (5) leads to: nv nv q- n,"

In an everyday situation, e.g., in a lecture hall with an air change of nv = 1.0 h -~, a typical stability ratio might equal about 0.6. Hence, the effective concentration of body odor might be only 60% of what would be expected if body odor were stable. Yaglou and Witheridge (1937) attributed the departure of ventilation requirements from proportionality during varying densities of occupancy to the instability of occupancy odor. Their finding that body odor

ASTM (1981) Recommended practice for referencing suprathreshold odor intensity. ASTM E 544-75, American Society for Testing and Materials, Philadelphia, PA. Berglund, L. G. and Cain, W. S. (1981) A ventilation and odor test facility, Int. J. Biometeor. 2,5, 3 , 2 4 3 - 2 4 8 . Cain, W. S., Leaderer, B. P., Isseroff, R., Berglund, L. G., Huey, R. J., Lipsitt, E. D. and Perlman, D. (1983) "Ventilation requirements in buildings: Control of occupancy odor and tobacco smoke odor", Atmospheric Environment, 17, 6, 1183 - 1197. Fanger, P. O. and Berg-Munch, B. (1983) Ventilation requirements for the control of body odor. Proceedings of an Engineering Foundation Conference on Management of Atmospheres in Tightly Enclosed Spaces, pp. 45-50. ASHRAE, Atlanta. Leaderer, B. P., Cain, W. S., Isseroff, R., and Berglund, L. G. (1984) Ventilation requirements in buildings. II. Particulate matter and carbon monoxide from cigarette smoking, Atmos. Environ.

18, 1, 99-106. Turk, A. (1963) Measurements of odorous vapors in test chambers: Theoretical, ASHRAE J. 9, 55-58. Yaglou, C. P., Riley, E. C., and Coggins, D. I. (1936) Ventilation requirements, ASHVE Trans. 42, 133-162. Yaglou, C. P. and Witheridge, W. N. (1937) Ventilation requirements (Part 2), A S H V E Trans. 43, 423-436.