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 3 mm 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 3 mm on the top and sides and 4 mm on the bottom. Total gap 0.01766 m2

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


Protecting individual doors.

The protection mechanism for individual doors is examined below based upon the assumption that only one door is open at any time. Within the overall supply volumes available it is not possible to provide protection for more than one open door at a time.

Lay-up Prep - Corridor door open.

Single door - Required flow 0.39 m3/s. (Sterile) - (Transitional)


A Lay-up Prep has a supply of 0.34 m3/s which due to the room pressure falling to 3 Pa is now directed across the open doorway and is augmented by the inward door leakage from the Theatre of 0.06 m3/s across a single door @ 22 Pa differential and thus the volume is achieved.

Lay-up Prep - Theatre door open.

Single door - Required flow 0.28 m3/s. (Sterile) - (Sterile)


Although both rooms are classified as Sterile the Lay up Prep is "more sterile" and therefore door protection is required. As there is a supply of 0.34 m3/s in the Lay up and the door leakage to the Corridor is reduced to 0.06 m3/s when the Lay up to Theatre door is open the required volume of 0.28 m3/s is available.

S.P.S Prep - Corridor door open.

Single door - Required flow 0.39 m3/s. (Sterile) - (Transitional)


When this door is open the pressure in the S.P.S. Prep drops to 3 Pa but there is insufficient supply volume to enable the door protection volume to be achieved unless the door transfer grille between Theatre and S.P.S. Prep is sized to pass 0.23 m3/s in the reverse direction to that of normal flow, which in itself is not entirely desirable. This figure is arrived at by taking the supply to the Prep of 0.1 m3/s plus the inward door leakage from the Theatre which will be 0.06 m3/s in this situation from the required door protection volume.

Theatre - Anaesthetic door open

Double door - Required flow 0.57 m3/s. (Sterile) - (Transitional)


When this door opens the pressure in the combined Theatre/ Anaesthetic becomes 17 Pa, which causes the stabilisers between Theatre and Exit Bay and Scrub and Corridor to close down diverting air across this doorway. The door leakage across the Anaesthetic to Theatre door increases to 0.1 m3/s and the stabiliser between Anaesthetic and Corridor has to be sized to handle 0.47 m3/s (@ 14 Pa differential) to provide an outflow path.

Theatre - Exit Bay door open

Double door - Required flow 0.75 m3/s. (Sterile) - (Transitional)


The pressure in the Theatre falls to 3 Pa when this door opens thus causing the stabilisers to the Anaesthetic and in the Scrub to close so diverting all the Theatre supply air across the doorway. In an S.P.S. Prep layout the Theatre has a supply of 0.75 m3/s which is adequate. In a Lay-up Prep layout the Theatre supply is normally only 0.65 m3/s but the Prep is supplying additional air to the Theatre and thus there is sufficient air to achieve protection.

Scrub - Corridor door open

Single door - Required flow 0.39 m3/s. (Sterile) - (Transitional)


Opening this door causes the pressure in the Theatre to fall to 3 Pa thus closing the stabilisers in the Theatre and diverting the required airflow across this door.

Theatre - Disposal door open

Single door - Required flow 0.47 m3/s. (Sterile) - (Dirty)


Opening this door causes the pressure in the Utility to rise to + 25 Pa but does not affect the pressure in the Theatre. Provided there is sufficient extract i.e. 0.41 m3/s and that the rise in pressure will now cause outflow to the Corridor of 0.06 m3/s a flow of 0.47 m3/s can be obtained across the Theatre to Utility door.

Where the Disposal adjoins the Dirty Corridor its extract is 0.1 m3/s which is insufficient to produce the required flow across the Theatre to Disposal door. It is therefore necessary to size the door transfer grille in the Disposal to Dirty Corridor door to pass 0.37 m3/s.

Anaesthetic - Corridor door open

Double door - Required flow 0.57 m3/s. (Clean) - (Transitional)


Opening this door causes the pressure in the Anaesthetic to fall from 14 Pa to 3 Pa (i.e. common pressure with the Corridor). The door leakage from the Theatre to Anaesthetic door increases to 0.1 m3/s and the stabiliser between Theatre and Anaesthetic has to be able to pass 0.47 m3/s (@ 22 Pa differential) to give the required flow of 0.57 m3/s across the open doorway.

Clean Corridor - Disposal door open

Single door - Required flow 0.28 m3/s (Transitional) - (Dirty)


Where the Disposal adjoins the Clean Corridor the extract required is 0.41 m3/s. The pressure in the disposal will become 3 Pa nominal when the door from the Clean Corridor is open reducing the inward leakage from the Theatre to 0.06 m3/s and thus there is sufficient extract volume to comfortably achieve door protection.

Disposal Corridor

Disposal Single door - Required flow 0 m3/s (Dirty) (Dirty)


No door protection flow is required.