Air Pressure Control Valves and Air Pressure Stabilisers

Door leakage and door protection in Operating Theatre Suites

Door leakage across closed doors (based upon HTM 03-01 figures)

Differential pressure - Pa
Door type 5 10 15 20 25 30 40
Single 0.03 0.05 0.06 0.06 0.07 0.07 0.08
Double 0.04 0.08 0.10 0.11 0.12 0.13 0.14
Hatch per lin. meter of 3mm gap 0.004 0.008 0.01 0.011 0.012 0.012 0.013

The leakages shown above are based upon the following door sizes :

Single doors - 2.01m high x 0.8m wide with gaps of 3mm on the top and sides and 4mm on the bottom. Total gap 0.01766 m2

Double doors - 2.01m high x 1.8m wide with gaps of 3mm on the top and sides, 4mm on the bottom and 2mm between leaves. Total gap 0.02688 m2.

Where doors are of different sizes or their gaps are not as above use the following formula.

Leakage = 0.827 x area of gap in m2 x sq. rt. of the differential pressure in Pa

Door Protection volumes in m3/s

Room Class Door type Dirty Transitional Clean Sterile
Sterile Single door
Double door		 0.47
0.95		 0.39
0.75		 0.28
0.57		 0 or 0.28
0 or 0.57
Clean Single door
Double door		 0.39
0.75		 0.28
0.57		 0 or 0.28
0 or 0.57		 -
Transitional Single door
Double door		 0.28
0.57		 0 or 0.28
0 or 0.28		 - -
Dirty Single door
Double door		 0
0		 - - -

Achieving Door Protection

The purpose of door protection is to provide a sweep of air across key open doorways to prevent, as far as possible the backflow of air from areas of lower cleanliness and thus the ingress of bacteria and other contaminants. Door protection volumes and velocities for standard Theatre layouts are indicated below.

Door location Room Classifications Door
Size		 Min*
flow
m3/s		 Min *
velocity
m/s
Lay up Prep - Theatre Sterile - Sterile Single 0.28 0.175
Lay up Prep - C. Corridor Sterile - Transitional Single 0.39 *1 0.243
S.P.S. Prep - C. Corridor Sterile - Transitional Single 0.39 0.243
S.P.S. Prep - Theatre Sterile - Sterile Single 0 *2 0
Theatre - C. Corridor Sterile - Transitional Double 0.75 0.208
Theatre - Anaesthetic Sterile - Clean Double 0.57 0.158
Theatre - Disposal Sterile - Dirty Single 0.47 0.293
Scrub - C. Corridor Sterile - Transitional Single 0.39 0.243
Anaesthetic - C. Corridor Clean - Transitional Double 0.57 0.158
C. Corridor - Disposal Transitional - Dirty Single 0.28 0.175

Notes

* These values are the minimum design values and in practice are exceeded in some cases.

*1 This volume is achieved by a supply of 0.34 m3/s in the Lay up, augmented by door leakage across the Theatre - Lay up door. This will be 0.06 m3/s as the pressure in the Lay up with the door to the Corridor open is 3 Pa.

*2 S.P.S Preps normally have a single door to the Theatre which is fitted with a door transfer grille. This should be sized to pass 0.23 m3/s when the Prep to Corridor door is open. Door leakage across the Prep - Theatre door will be 0.06 m3/s (single door @ 22 Pa) in this condition thus providing a total of 0.39 m3/s for door protection across the S. P. S. Prep to Corridor door.

There should be no door between Scrub and Theatre.

Double doors should be avoided between the Theatre and Disposal unless the nett inflow to the Theatre (supply plus inflow from Prep) is increased to at least 0.95 m3/s.

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