Evaluation of draught in surgical operating theatres ... - Emerald

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JFM
9,1
64
Received April 2010
Accepted May 2010
PRACTICE BRIEFING
Evaluation of draught in surgical
operating theatres: proposed
revision to (NEN)-EN-ISO-7730
Paul Roelofsen
Grontmij/Technical Management, Amersfoort, The Netherlands
Abstract
Purpose – The purpose of this paper is to show that it is advisable to evaluate draught in an operating
theatre in a different manner than the method according to NEN-EN-ISO-7730. The NEN-EN-ISO-7730 is
an international standard for the analytical determination and interpretation of the thermal comfort of
the human body and the local thermal comfort like for instance draught.
Design/methodology/approach – Using a CFD computer program, it is possible to evaluate
draught in an operating theatre in the design stage, according to different mathematical draught models.
Findings – It would seem advisable to begin with the draught model developed by Griefahn.
The model does, however, need to be modified to include the effects of temperature sensation and the
direction of the air stream, so that it becomes applicable to a thermally cool environment (PMV , 0) and
a vertical air stream, the air pattern prescribed for an operating theatre.
Originality/value – It can be demonstrated that by implementing the proposal in this paper in a CFD
program, the possibility exists to be able to evaluate, in a responsible fashion, the results for a much
broader range of parameters than is currently possible by means of the NEN-EN-ISO-7730.
Keywords Operating theatres, Temperature, Air, International standards
Paper type Research paper
Journal of Facilities Management
Vol. 9 No. 1, 2011
pp. 64-70
q Emerald Group Publishing Limited
1472-5967
DOI 10.1108/14725961111105736
Introduction
In The Netherlands, almost all surgical operating theatres are provided with a supply air
plenum having dimensions of 1.2 £ 2.4 meter. The application of such a plenum is
extremely important in order to ensure that filtered clean air flows from the whole plenum
area vertically downwards over the open incision of the patient and, to a certain extent,
also over the operating team and tables upon which the surgical instruments are laid out.
Nowadays, due to new insights into infection prevention, the air distribution within
an operating theatre proposes to use a much larger supply air plenum of 3.5 £ 3.5 meter
together with a proportionally larger supply air quantity. In this manner, the operating
table, the operating team and the surgical instrument tables are fully enveloped by the
clean, filtered air from the ceiling. As a consequence, the surroundings and adjacent
rooms become less critical objects since the chances of bacterial contamination are
significantly reduced.
Such developments, therefore, not only have an impact on the technical installations but
also on the layouts of the surgical departments (College bouw ziekenhuisvoorzieningen,
2003).
Owing to the larger plenum and supply air volume, the members of the surgical team
would now be “washed over” with cooled air, and as a consequence of the differing

activity levels and clothing, it is appropriate to consider any effects of unwelcome
draughts which may occur.
Draught
Draught is defined as an unwelcome cooling of a part of the human body as a result of
air movement.
Draught, conforming to NEN-EN-ISO 7730
Currently, it is conventional to determine the effects of comfort, caused by draught,
through the use of a mathematical skin model, whereby the percentage of complainants
can be calculated and predicted using the parameters of air temperature, the average air
speed and air turbulence intensity, in accordance with NEN-EN-ISO 7730 (2005)
(Figure 1). The NEN-EN-ISO-7730 is an international standard for the analytical
determination and interpretation of the thermal comfort of the human body and the local
thermal comfort like for instance draught.
This draught model was based upon a study of 150 test persons, in an air temperature
between 208Cand268C, an average (horizontal) air speed of between 0.1 and 0.4 m/s and
a turbulence intensity between 10 and 70 per cent. The model is specifically applicable to
occupants with a low activity level, i.e. in the main seated (metabolism

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66
The application of the aforementioned comfort draught model would not appear to be
appropriate for evaluating discomfort due to draughts in an operating theatre.
The following parameters used in the comfort model, therefore, cannot be applied
and need to be re-assessed:
.
the metabolic rate and the activity;
.
the temperature sensation (m.n. PMV , 0); and
.
the direction of airflow.
Influences of metabolism and activity upon the sensation of draught
Studies carried out by Toftum (1994) (Figure 2) and Griefahn (1999) (Figure 3) give an
indication as to how far the metabolism and externally transmitted activity heat
influences draught.
The draught models of Toftum and Griefahn are based upon the draught model
conforming to NEN-EN-ISO-7730.
In Table I, a comparison is shown between the applicable parameter ranges for the
various draught models.
From Table I, it would appear that the draught model formulated by Griefahn has
the largest applicable parameter range. The Griefahn experiments show that the model
which had been developed by them had the largest correlation with the experimental
results. Discomfort, due to draught, formulated by Griefahn, may be calculated using
the following formula:
Draught rating (%)
25.00000
23.43750
21.87500
20.31250
18.75000
17.18750
15.62500
14.06250
12.50000
10.93750
9.375000
7.812500
6.250000
4.687500
3.125000
1.562500
0.000000
Probe value
2.017788
Average value
5.177231
Figure 2.
Conforms to Toftum
(1994)
FLAIR
OPERATING THEATRE

Draught rating (%)
25.00000
23.43750
21.87500
20.31250
18.75000
17.18750
15.62500
14.06250
12.50000
10.93750
9.375000
7.812500
6.250000
4.687500
3.125000
1.562500
0.000000
Probe value
3.714398
Average value
9.530385
Surgical
operating
theatres
67
FLAIR
OPERATING THEATRE
Figure 3.
Conforms to Griefahn
(1999)
Draught model
Metabolism
(W/m 2 )
Air temperature
(8C)
Average air speed
(m/s)
Turbulance intensity
(%)
NEN-EN-ISO-7730 (2005) < 70 20-26 0.1-0.4 10-70
Toftum (1994) 104-129 11-20 0.1-0.4 10-40
Griefahn (1999) < 60-156 11-23 0.1-0.4 20-90
Table I.
Applicable ranges for
the draught models
PD ¼ðtsk 2 taÞ ·ðva 2 0:05Þ 0:623 ·ð3:143 þ 0:37 ·va·TuÞ·ð1 2 0:0061 ·ðM 2 W 2 70ÞÞ
where
PD ¼ the percentage dissatisfaction as a result of draught (per cent);
t sk
t a
v a
Tu
M
¼ 32.3 þ 0.079 * t a 2 0.019 * (M 2 W) (8C);
¼ the air temperature (8C);
¼ the average air speed (m/s);
¼ the turbulence intensity (per cent);
¼ metabolic rate (W/m 2 ); and
W ¼ externally transmitted, activity related, heat rate (W/m 2 ).

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Influence of temperature upon sensitivity to draught
Another study carried out by Toftum and Nielsen (1996) showed that the sensation of
cooler/colder temperatures (PMV , 0) significantly increases discomfort.
Consequently, the percentage dissatisfaction, as a result of the sensation of draught,
was greater as a result of cooler/colder temperatures than by neutral (PMV < 0)
temperature. This also seems to explain why persons, active in a cooler environment,
complain of draught even when the average air speed is lower.
The influence of the temperature sensation upon discomfort, as a result of draught,
is calculated by the following formula presented by Toftum:
PD cool
100
¼
PD neutral ð1 þ expð2b:TMV cool 2 lnðPD neutral =ð100 2 PD neutral ÞÞÞ :PD neutralÞ
where
PD neutral ¼ percentage dissatisfaction as a result of draught with a neutral
temperature sensation (PMV < 0) (per cent);
PD cool
ß
¼ percentage dissatisfaction as a result of draught in a cooler environment
(per cent);
¼ regression coefficient: 20.829 (2); and
TMV ¼ temperature sensation in a cool environment (PMV , 0) (2).
Influence of air flow direction upon draught
All the previously mentioned draught models are based upon a horizontal air stream.
Other studies (Zhou, 2004; Mayer and Schwab, 1990) indicate that the air stream
direction has a dramatic effect upon the feeling of draught discomfort. Occupants
subject to an airflow in a downward direction appear to be less conscious of draughts
than when in a horizontal air stream.
The influence of the flow direction upon discomfort as a result of draught is
expressed in the following formula, developed by Genhon Zhou, below:
PD flow direction
PD neutral
¼ expðd:ðta 2 24ÞÞ ½2Š
where
PD flowdirection
d
t a
¼ percentage dissatisfaction as a result of flow direction (per cent);
¼ coefficient, conforming to Table II (2); and
¼ air temperature (8C).
Table II.
Coefficient (d) dependent
upon the flow direction
Flow direction
d
Vertically downwards 0.12
Horizontal 0
Vertically upwards 20.05

Calculation results
To give an idea of how the calculated results differ from each other and with the aid of
a CFD computer program, the percentage dissatisfaction has been calculated for each
model in an operating theatre with a supply air plenum of 3.5 £ 3.5 m.
The following parameters, for a surgeon (Melhado et al., 2005), have been used:
.
Metabolism: 128 W/m 2 .
.
Mechanical efficiency: 0.086 (2).
.
Intrinsic clothing resistance: 0.95 clo.
Surgical
operating
theatres
69
Conclusion and advice
It is evident that the draught model conforming to NEN-EN-ISO-7730 is not applicable
for evaluating draughts in an operating theatre or in any other situations where
occupants are not performing a calmly sitting activity (M

JFM
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Advice
.
To further investigate in how far the influence of the air direction, of which the
sensation of draught could be a function of the metabolism, may not be being
fully taken into account in the Griefahn formula.
.
The (NEN-EN-)ISO 7730, pertaining to draught, should be reviewed and
improved upon, for example, in the manner mentioned herein.
References
College bouw ziekenhuisvoorzieningen (2003), In Perspectief nr.5, available at: www.
bouwcollege.nl/Pdf/CBZ%20Website/Publicaties/In%20perspectief/inperspectief5.pdf
Griefahn, B. (1999), Wirkung und Bewertung von Zugluft am Arbeitsplatz, Institut für
Arbeitsphysiologie an der Universität, Dortmund.
Melhado, M.A., Beyer, P.O., Hensen, J.M. and Siqueira, L.F.G. (2005), “Study of the thermal
comfort, of the energy consumption and of the indoor environment control in surgery
rooms”, Proceeding Indoor Air, Tsinghua University, Beijing.
Mayer, E. and Schwab, R. (1990), “Untersuchung der physikalischen Ursachen von Zugluft”,
Gesundheits Ingenieur – Haustechnik – Bauphysik – Umwelttechnik, Vol. 111 No. 1,
pp. 17-30.
NEN-ISO-7730 (2005), “Ergonomics of the thermal environment – Analytical determination and
interpretation of thermal comfort using calculation of the PMV and PPD indices and local
thermal comfort criteria”, available at: www.bouwcollege.nl/Pdf/CBZ%20Website/
Publicaties/In%20perspectief/NEN_EN_ISO_7730 (2005 dec).pdf
Toftum, J. (1994), Traekgener i det industrielle arbejdsmiljø, laboratoriet for varme-og
klimateknik, Danmarks Tekniske Universitet, Copenhagen.
Toftum, J. and Nielsen, R. (1996), “Draught sensitivity is influenced by general thermal
sensation”, International Journal of Industrial Ergonomics, Vol. 18, pp. 295-305.
Zhou, G. (2004), “Impact of airflow direction on perceived draught discomfort”, available at:
www.ie.dtu.dk/resresults.asp?ID¼25
Further reading
CR-1752 (1999), “Ventilatie van gebouwen – Ontwerpcriteria voor de binnenomstandigheden”,
available at: www.bouwcollege.nl/Pdf/CBZ%20Website/Publicaties/In%20perspectief/
NPR1752.pdf
Fanger, P.O. and Christensen, N.K. (1984), Perception of Draught in Ventilated Spaces,
Laboratory of Heating & Air Conditioning, Technical University of Denmark.
Corresponding author
Paul Roelofsen can be contacted at: paul.roelofsen@grontmij.nl
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