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NATIONAL BUREAU OF STANDARDS REPORT

65^5

PROGRESS REPORT

ON

VENTILATION STUDIES AT LOCHRAVEN HOSPITAL

FOR THE PERIOD

(September 1, 1958 to June 30, 1959)

by

Carl W. Coblentz

Paul R. Achenbach

Edward F. Kramer

Report to

Department of Medicine and Surgery

Veterans Administration

Washington, D. C.

<QJBS>

0. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards'; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

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problems; invention and development of devices to serve special needs of the Government; and the

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research, development, engineering, instrumentation, testing, evaluation, calibration services, and

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Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards. Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1000-20-10433 September 21, 1959

NBS REPORT

6545

PROGRESS REPORT

ON

VENTILATION STUDIES AT LOCHRAVEN HOSPITAL

FOR THE PERIOD

(September 1, 1958 to June 30, 1959)

ty

C. W. Coblentz, P. R. Achenbach, E. F. Kramer

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Department of Medicine and Surgery

Veterans Administration

Washington, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ST

intended for use yvithin the

to additional evaluation and i listing of this Report, either the Office of the Director, N< however, by the Government

to reproduce additional copit

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

rogress accounting documents

mally published it is subjected

reproduction, or open-literature

»ion is obtained in writing from Such permission is not needed,

prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

- 2 -

(f) The effect of opening windows on the natural convection

air exchange in individual rooms.

(g) The effect of wind velocity and direction on the ventilation of individual rooms and the wing as a unit.

It was planned that the helium tracer gas technique, thermocouple anemometers, and other apparatus for measuring air exchange

and air velocity would be used in carrying out this investigation.

2. DESCRIPTION OF TEST SITE AND APPARATUS

Four rooms, on the fourth floor of wing B in the Lochraven

Hospital were used for most of the observations. The four rooms.

No. 4-19, 4-20, 4-21, and 4-23, were in line on one side of the

hall as indicated in Fig. 1. All four rooms had a northern exposure and. were heated by steam convectors located under the

windows. The heat output of the convectors was manually adjustable

by a hand valve accessible to the occupant of the room. The occupants were free to open the windows as desired.

During the heating season, the fresh air for this ward was

introduced at the end of the hall by means of a blower and thermostatically-controlled steam convector unit that was installed underneath the window. This convector is also indicated in Fig. 1.

Since the patient rooms were equipped with manually-controlled steamheated convectors, it was not possible to balance the temperature

In these rooms with that in the hall during the test, when the doors

of the rooms were closed.

The infiltration meter used for the tests consisted of twelve

sensing probes and cables connected to a console containing the

regulating and bridge circuits for measuring the relative helium

concentrations at selected intervals. Each sensing probe consisted

of an aluminum block with two identical cylindrical cavities containing matched thermistors. One cavity was hermetically sealed,

the other ventilated by natural convection of the helium-air mixture

in the room in which it was located. By Incorporating the two

heated thermistors in a bridge circuit, the thermal conductivity

of the helium-laden air could be used to monitor the decreasing

helium concentration in a room as a result of fresh air leakage.
.

;
I AYOUT OF TEST AREA

- 3

-

The thermocouple anemometer used for air velocity measurements was designed and built by the National Bureau of Standards

for directional measurements of low air velocity. It incorporated two pairs of hot and cold junctions heated by a small alternating current. Small diameter wire was used for two of the

junctions and larger wire for the other two. Thus the small

junctions were heated more by the alternating current than the

larger ones, and a small thermoelectric emf was produced which

could be related to the air velocity over the junctions by calibration. This type of instrument is especially sensitive at low

air velocities in the range from 5 to 100 feet per minute.

The Lochraven Hospital contained a pilot ward consisting of

6 patient rooms and two lavatories separated from the main corridor of wing 4-B by an auxiliary corridor. Two doors connected

the main and auxiliary corridors. This ward was occupied by

patients with active tuberculosis and was used by the medical

research staff for studies designed to show whether or not live

tuberculosis organisms could be carried from the rooms through the

ventilating system to the upper floor and produce tuberculosis

infection in guinea pigs who breathed the air.

The ventilating system of the pilot ward consisted of a blower and duct system in a roof laboratory above the ward which

recirculated large quantities of air through the pilot ward and

diverted a smaller amount through the animal chambers before discharging it outdoors. In this system the fresh air supplied to

the pilot ward equalled the amount diverted through the animal

chambers. The windows of the pilot ward were carefully sealed

with plastic sheeting and masking tape so the blower would produce a small negative pressure in the pilot ward relative to the

main corridor. Several measurements of the ventilation rate in

the pilot ward were made in 1956 using the tracer gas procedure.

Recently,, a second animal chamber was installed in the roof

laboratory to compare the rate of infection of the animals by

the air from the pilot ward with and without germicidal lamps in

the ducts supplying the animal chambers. A method for delivering

equal volumes of air to the two chambers was required. The recirculating feature of the ventilating system was also blocked off

and only the amount of air needed for fresh air makeup in the pilot

ward was supplied to the animal chambers.

-4-

3. TEST PROCEDURES

3.1 Tracer Gas Techniques

In initiating the project,, the first two months were used for

building a new infiltration meter that was better adapted to this

particular testing work than the model then on hand. It used

aluminum for housing the sensing elements instead of brass, which

was more pervious to helium gas, and was designed for a greater

sensitivity to reduce the amount of helium required as a tracer

gas. A complete recalibration was required due to the fact that

the indicating meter used in the first model was no longer available from the factory and another kind of micro-ammeter had to be

adapted to the new apparatus.

During the first visit to the hospital on October 22, 1958,

it was found that the clearance between the doors and the floor

was so small that the cables for the sensing probes could not be

put through the closed doors between hall and patient rooms. A

semi-permanent installation, therefore, was necessary and the

cables were placed in the false ceiling of the halls and then

through holes in the walls which led into the four patient rooms

designated as the preliminary test area.

The first investigation to be made was the determination of

the air exchange between these patient rooms and the hall. This

was to be accomplished by introducing helium as a tracer gas into

one or several of the rooms. Four rooms in the 4-B ward. Nos.

4-19j> 4-20, 4-21 and 4-23^ were equipped with 3 sensing probes

each. The console was placed against the corridor wall between

rooms 4-23 and 4-24. Three cables terminated in each of the four

rooms about 3 ft above the floor; the probes were connected to

these ends. The other ends of the cables were arranged to hang

down through an opening in the false ceiling for connection to

the console during the test; and to be stored above the false ceiling when not in use.

The temperature in the hall and in the rooms was determined

with thermometers, at the outset. It was found that this was not

satisfactory, however, and a series of 19 thermocouples was installed bn the walls of the hall and of the four rooms with the

junctions about 1 1/2 inches off the wall.

-5-

The method used for determining the air exchange between the

patient rooms and the corridor, when the doors are open, was a modification of the tracer gas method as used for determining the

air change rate of an enclosure. The air change rate of an enclosure is usually defined as the ratio of the hourly rate at

which the air enters (or leaves) the enclosure to the volume of

the enclosure.

The rate of change in concentration of a tracer gas caused by

infiltrating outside air can be expressed by the formula:

-V (dc/dt) = Kc (l)

where: V = volume of the enclosure

c = concentration of tracer gas at time t

K = average volume of air infiltration per unit time

for the time interval

When c = c Q at t = 0, the solution of the above equation is

c - c e- KtA (2)

or Kt/V = In (c Q/c) (3)

which indicates that the number of air changes occurring during

the time t is equal to the natural logarithm of the ratio of the

tracer gas concentrations at the beginning and at the end of this

time interval.

3.2 Air Plow Measurements with an Anemometer

A series of tests was made to determine the air flow rates

through the open door of one room by use of a thermocouple anemometer. These tests were made to confirm the results obtained

with the tracer gas method, as there was some question whether

or not opening of the doors for only two minutes would produce a higher air exchange rate between room and corridor than if the

door was open continuously.

- 6 -

For this purpose the air velocity was measured at 6 inches

and 18 inches below the top of the door and also the same distances

from the floor. At the same time the direction of the air flow was

determined with a smoke gun.

Similarly, the air flow through the doors of the first 12

rooms of the 4-B ward (see Fig. l) and the flow from this wing

toward the center of the building was measured using the thermocouple anemometer. This test was conducted at an outside temperature of 94°F with practically no wind. Almost all of the

windows in the ward were open.

4. TEST RESULTS

The ventilation rates of rooms 4-lSh 4-21, and 4-23 were observed a number of times between November 1958 and April 1959^

for a total of 27 measurements under heating conditions. These

measurements were made with the doors closed and with the doors

open using the helium tracer gas technique. The temperature difference between the corridor and the room was observed in most

cases. Table 1 summarizes the results of these tests.

Some correlation between ventilation rate and the temperature

difference between the corridor and room can be seen in Table 1

when the doors were open, but there are a number of inconsistencies. It would be expected that the difference in air density

caused by temperature difference would be the principal motive

force for air exchange through the open doors, but outdoor wind

velocity and direction probably had some effect. The measured

air flow through the open doors ranged from 55 to 337 cfm per degree temperature difference with an average of 115 cfm per degree.

The median value for air exchange through the open doors was 80 cfm

per degree temperature difference.

The ventilation rate with closed doors ranged from 7 to 68 cfm

with an average value of 23 cfm for all the tests. The ventilation rate with closed doors would be more closely related to the

outdoor temperature, wind velocity and direction, and to the tightness of window closure.

Table 1 indicates that the higher values of ventilation with

doors closed, occurred when the wind was from the southeast or

southwest which would tend to increase the static pressure at the

outdoor air intake of the steam convector in the hall.

Ventilation

of

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-8 -

Thus the average air change rate in the rooms with the doors

closed, which was probably not all fresh air from outdoors, was

about one per hour, whereas the average air change rate between

corridor and each room with the doors open was about six per hour

in terms of the room volume.

During winter conditions, the air delivery of the steam convector unit at the end of the hall was 1080 cfm with the air filters clean. One measurement made with the filters dirty indicated an air delivery for the convector unit of only 375 cfm of which

about 100 cfm was recirculated air.

Fig. 2 is an illustration of the method of evaluating the test

data when using the tracer gas technique. Referring to equation ( 3 ) cited in the Test Procedure, it is seen that the logarithm of the

ratio of the initial and final helium concentration will be a

constant if the rate of fresh air leakage is a constant, that is,

if the forces producing air leakage remain steady. Thus the value

of the concentration of helium plotted against time on semilogarithmic paper would be a straight line. In Fig. 2, the rate

of air leakage with the doors closed can be determined from the

slope of the straight line through the plotted points for the

period from 0 to 20 minutes. The break in the line shown at 20

minutes was caused by an arbitrary change in amplification of the

bridge circuit signal, but the slope of the decay curve remained

constant as long as the doors remained closed.

The doors were opened for 2 minutes at 25 minutes after the

start of the test. About 7 minutes were required after closing the

door to re-establish a well-mixed condition in the room between

the helium-laden air and the air entering from the corridor, after

which the decay curve returned to the same slope as before the doors

were opened. The change in concentration caused by opening the door

can be evaluated by the distance separating the center and right

hand portions of the decay curve at constant slope. For the test,

illustrated in Fig. 2, the ventilation rate with the door closed

was 31 cfm and with the door open was 216 cfm.

When measuring the air flow through an open door with the

thermocouple anemometer, it was found that the velocity fluctuated

considerably and even changed direction sometimes during a single

set of observations. It was necessary, therefore, to take the

average of a number of observations to obtain useful values. When

the magnitude and direction of the air flow was plotted against

VENTILATION WITH OPEN AND CLOSED DOORS

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-9-

height above the floor, it was found that the velocity pattern

was approximately a straight line with a neutral zone somewhat

above the center of the door opening at which there was a negligible air motion. This pattern is illustrated in Fig. 3 which

represents the average results of nine tests in room 4-23 with

a temperature difference of 1.3°F between room and corridor.

The height of the door was 83 inches and the width 42 inches.

Based on the indicated velocity pattern in Fig. 3* the neutral

zone was about 50 inches above the floor for these conditions.

The indicated air flow from the room to the hall would be

42 x 50 x 13.3

2 x 14'4' 97 cfm and

the flow from hall to room would be 42 x 33 x 8.75

2 x 144 42 cfm

corresponding to a net exchange of 55 cfm. The direction of air

flow in the upper and lower parts of the doorway would depend on

the relative temperature levels in the two spaces. The difference

between the inward and outward flow through the connecting door

would be equal to the window leakage, if the remainder of the room

was airtight. The following table shows the results obtained with

this method during several sets of observations.

Table 2

Air Flow Measurements Through Door

(Determined with an Anemometer)

Temp. Diff.

°F

Air Flow

into room

Rate, cfm

from room

No . of

Tests

1.3 42 97 9

3.2 67 455 7

3.3 48 509 15

AIR FLOW THROUGH OPEN DOOR

-IpSimilarly, the air flow through the doors of the first 12

rooms in Ward 4-B and the flow in the corridor from this wing

toward the center of the building was measured when the outdoor

temperature was about 94 °F . There was practically no wind and

the windows in most of the patient rooms were open. The air

velocities were not steady at any point and, at times,, the flow

changed direction at a given station, so the measurements only

indicate the order of magnitude of the air exchanges.

The net air flow rate through the windows in the patient

rooms was computed as the difference between the inward and outward flow to the room at the hall door. The air movement toward

the corridor and from the corridor at each of the 12 door openings is shown in Table 3. Fig. 7 shows a floor plan of the test

area in which the values of Table 3 and also the air flow rates

determined in the corridor are marked as arrows with the respective flow rates in cfm. In many cases, there was one-way flow

only at the door, but in a few cases there was two-way flow. In

6 of the 12 rooms there was flow only from the room to the corridor, in amounts ranging from 317 to 2380 cfm, whereas the air

flow was entirely from corridor to room in 3 other cases, in

amounts ranging from 195 to 1463 cfm. The net air movement toward

the corridor for the twelve rooms was 5373 cfm and an additional

2835 cfm was recirculated between rooms and corridor. The total

air exchange between corridor and rooms represented about 8l air

changes per hour with respect to the corridor volume. There was

undoubtedly more fresh air exchange through the windows in the

patient rooms, in most cases, than is indicated by the net air

exchange at the doors in Table 3 , because there were movable frames

at three heights in each window. This would provide a ready means

for two-way air flow at the windows under the influence of stack

effect in the rooms.

In addition to the net flow of 5373 cfm from the 12 rooms

toward the hall, an additional 2449 cfm entered the corridor through

the window at the end of the hall indicating a total rate of air

movement of 7822 cfm toward the center of the building. Measurements of the air flow in the corridor toward the center of the

building at a distance of 72 ft from the end, indicated a flow

rate of 6926 cfm toward the center of the building of which 606 cfm

was flowing through the space above the false ceiling in the corridor.

Thus a discrepancy of about 900 cfm is indicated between the air

movement in the corridor toward the center of the building as measured

72 ft from the end and the sum of the net air movement through the

- 11 -

Table 3

Room Air Flow through Doors in Patient Rooms, cfm

Number To Corridor From Corridor Net Air Exchange

19 317 0 317

20 453 0 453

21 0 195 195

23 0 806 806

24 47 57 10

25 1536 0 1536

30 0 1463 1463

32 2380 0 2380

34 1684 0 1684

36 1028 129 899

37 324 185 139

38 439 0 439

- 12 -

room doors and that entering the window at the end of the hall.

This difference Is not unexpected considering the fluctuations

observed during the measurements.

It had been planned that the air movement from one patient

room to the adjacent one by way of the corridor would be measured

during the series of tracer gas studies summarized in Table 1.

Only in two of the fourteen tests was a trace of helium detected

in the next room when the doors were closed after the 2-minute

opening period. Since a flow of about 60 cu ft of air (heliumcontaminated) from one room to the next room would have produced

a measurable deflection on the indicating meter of the instrument

in the second room,, it appears that this air flow rarely reached

a rate of 30 cfm.

This conclusion was corroborated by the measurements of the

air velocities in the door areas by means of an anemometer. It

was found that on the same side of the corridor the air movement

from corridor to rooms was always either through the lower or

through the upper part of the doors, depending on whether the

hall or the rooms were warmer and upon the direction of the wind.

If helium-contaminated air left one room through the upper portion

of its door and air moved into the next room through the lower

part of its door. It appears likely that only through very considerable turbulence in the corridor would it be possible for a

significant amount of air to flow from one room into the adjacent

one. Only if the temperature gradient between the two rooms and

the corridor was opposite in direction could a considerable air

movement from one room to the next one be expected. This was the

case in one of the two instances when helium was detected in the

next room.

5. VENTILATION OF THE PILOT WARD

In order to evaluate the infectivity of the air from the pilot

ward when circulated through the animal chambers, the air change

rate of the ward had to be kept constant. The ventilation rate

should be set at the minimum required for the needs of the patients in the pilot ward. A ventilation rate of 30 cfm per patient,

that is, a total ventilation rate of 180 cfm was selected.

The large Trane ventilating blower which had been used for

recirculation of large quantities of air to the pilot ward was

by-passed and a new blower, ILG type PE-4 rated at 195 cfm with

-13-

2 3/4 in. W.G. pressure drop, was installed. An orifice plate, of

a size calculated to produce about 1 in. W.G. pressure drop, was

provided in each of the 10 in. diameter ducts to the animal chambers. This arrangement was intended to produce equal flows of air

to both animal chambers even when one of them was open for servicing. Several tests of the ventilation of the pilot ward were

made with this arrangement which led to the detection of a leak

in one of the window seals. In order to reduce the transmission

of blower noise into the ward through the duct system, a 5-ft

length of sound-absorbing duct was installed, and the blower was

mounted on, an elastic pad.

The ventilation rate determined in the pilot ward by means of

the helium decay method was 0.886 air changes per hour. Since the

total volume- of the ward was 11,320 cu ft, this corresponded to a rate of 167 cfm. This flow rate was corroborated by the manufacturer’s flow-pressure curve for the pressure observed across

the blower. This curve indicated an air flow rate of 176 cfm for

the observed pressure drop of 3.00 in. W.G. across the blower;

which was 9 cfm, or 5 percent, higher than the value determined

with the helium decay method. This agreement was considered satisfactory. It also indicated that all of the air that passed through

the blower had come from the pilot ward, a fact which could not be

determined otherwise, since the ducts were so enclosed in the ceiling that a visual inspection of their tightness was not possible.

When the decay rate of E coll bacteria passing with the air

stream through the blower was determined by the medical research

staff at Lochraven Hospital, it was found that the rate was excessive and was impeding the bacteriological test procedure. The

high speed of the blower (3400 rpm) was considered a possible cause

of the destruction of the bacteria. It was, therefore, decided to

return to the original large blower system which could be reconnected to the ducts without too much alteration. The discharge

pressure of this blower at its operating speed of 212 rpm was determined to be 0.07 in. W.G. with the discharge blocked. The ventilation of the pilot ward was measured by the helium decay method with

the blower operating at this speed. Two tests were conducted on one

day which indicated ventilation rates of 263 cfm and 280 cfm, respectively. This ventilation rate was higher than desired, and the

variation of 17 cfm between the two values was thought to have, been

caused by the small pressure drop in the ventilating system and the

changes in the outside temperature between the morning and afternoon test.

-14-

An attempt was made to stabilize the flow rate by introducing a flow resistance in the system. The orifice plates in

the 10 in. duct were increased to 7 1/2 inches in diameter which

was calculated to produce a pressure drop of approximately 0.01

in. W.G. at an air flow rate of 120 cfm in the duct to each

animal chamber. This flow resistance was introduced to reduce

the air flow through the blower, somewhat, and also to assist in

stabilizing the flow rate. Three tests made under this condition

indicated flow rates (ventilation of the pilot ward) of 217 cfm,

232 cfm and 233 cfm, respectively.

The decay measurements originally conducted inside the pilot

ward represented too great a hazzard for the test personnel who

had to spend about 5 hours in the ward. Therefore, the installation

of the instrumentation was discontinued in the ward and it was moved

up to the roof laboratory where several probes were placed in the

ventilating duct from the ward. Fig. 4 and Fig. 5 show graphs of

the observed concentration rates. It will be noted that the plotted

observations in Fig. 4, which was conducted inside the pilot ward,

fall much closer to the straight line on semi-logarithmic paper

than those of Fig. 5 which were determined from the roof laboratory. The cause of the fluctuating decay rate in this study could

be due to inadequate mixing of the helium in the ward since the

deviations from the straight line coincide on all three probes.

6. DISCUSSION AND CONCLUSIONS

The average air exchange rates observed during the heating

season in the four test rooms of Ward 4-B are shown diagrammatically

on the floor plan in Fig. 6 for a selected group of tests. By

making certain assumptions, the concentration of a contaminant or

contagion in any one of the rooms or at any station in the corridor

under steady state conditions can be computed for selected rates

of generation of contagion in each room and ventilation with fresh

air. The following assumptions were made for the present analysis:

(a) the air exchange rate through each of the windows was

equal to the average value observed for four of the

rooms,

(b) the air exchange rate between each room and the corridor was equal to the average value observed for the

four test rooms.

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VENTILATION PATTERN UNDER HEATING CONDITIONS

AVERAGE

AIR

FLOW

THROUGH

WINDOWS

23

CFM

-15-

(c) the fresh air supply rate through the hall convector

was equal to that measured when the filter in the

convector was clean,

(d) the fresh air entering the windows left each room by

way of the door to the corridor,

(e) the air entering the rooms through the windows and

doors was thoroughly mixed with the room air,

(f) the air exchanged between corridor and rooms was

thoroughly mixed with the corridor air, downstream

from the door opening, and

(g) one unit per minute of contagion or tracer gas was

introduced into each room.

The values for the concentration of contagion or tracer gas

in units per thousand cubic feet of air in a ward with ten rooms

located symmetrically on each side of the corridor for the conditions assumed above are summarized in Table, 4. Under steady

state conditions these concentrations would be independent of the

size of the rooms and corridor sections, and depend only on the

magnitudes of the air exchange rates.

Table 4

Concentration of Contaminant Along The Corridor

and In The Rooms of A Hospital Ward

(Under ventilating conditions shown in Fig. 6)

Order of Location of

Room Pairs on each

Side of Corridor

Concent rat ion of Contaminant

units per 1000 cu ft

Room Corridor

1 3.00 1.78

2 4 . 66 3.40

3 6.17 4.92

4 7.58 6.33

5 8.90 7.64

6 10.10 8.84

7 11.22 9.97

8 12.27 11.03

9 13.25 12.05

10 14.20 12.98

- 16 -

The equations used to determine the concentrations shown

in Table 4 are:

C rm

1 ) Qc + ^

Qc +

C

n = 2mb

m T 7

Qh 1 2m Qp

where

:

m = the number of the symmetrically-placed pair of rooms

on either side of the corridor numbered from the end

of the corridor

Qr = rate of fresh air entry at each room window,, cfm

Qc = rate of air exchange between corridor and each room, cfm

\

Qh

= rate of fresh air entry through hall convector,

Nsd’m

b = number of units of contagion or tracer gas per minutK

released in each room \

C-p = concentration of contaminant in rooms m x m

C

Q = concentration of contaminant in corridor space between

m rooms m and m + 1.

It will be noted that the concentration in the first pair of

rooms, which exchanged uncontaminated air with the corridor, was

only 21 percent of that in the tenth pair under steady state conditions and 23 percent of the concentration in the corridor just

after the tenth room door. The corridor concentration outside a given room door ranged from a minimum percentage of 59.3 of the

concentration in the corresponding room for room 1 to a maximum

percentage of 91.4 for room 10. The concentrations in the various

rooms and parts of the corridor would be changed somewhat, if the

-17-

hospital wing were pressurized so the flow of air through the

window cracks was outward instead of inward as assumed for this

analysis

.

Since the air leakages through all of the windows and the air

exchanges through all of the hall doors were not equals there wou}.cl

be variations from the values of concentration summarized in

Table 4. Also,, imperfect mixing of the air in the corridor might

cause the concentration of contaminant to be higher near the

ceiling than near the floor, or vice versa, depending on the

relative temperature levels in the corridor and rooms. However,

the analysis of the winter time ventilation pattern illustrated

in Fig. 6 reveals two important conclusions; first, that the high

air exchange rate through the doors to the corridor causes the concentration of contaminants in the corridor to approximate that in

the rooms and; second, the concentration of contaminants increases

many fold from the fresh air inlet to the points of air exhaust

toward the center of the building.

Figure 7 shows diagrammatically the air exchanges that occurred through the doors between the various patient rooms and the

corridor during a hot summer day when the outdoor temperature was

about 94°F, with practically no wind, and with most of the windows

open. In this figure the flow of air through the windows is shown

as equal to the net exchange through the corresponding door.

Actually, more fresh air could have moved through the windows than

is indicated because there were three movable frames in each window at different levels. The air flow vectors in Fig. 7 indicate

a rather free exchange of air between spaces and reveals no simple

pattern. For purpose of analysis it was assumed that the air exchange was so unrestricted that the twelve rooms could be considered

as one large room with 12 units of contaminant and a total of

10,350 cu ft of fresh air introduced per minute. Under steady

state conditions, this would correspond to an average concentration of 1 . 16 units of contaminant per thousand cubic feet of air

for the whole space. This value is about one third that computed

for the first pair of rooms under winter conditions. Undoubtedly,

the average and local concentrations would vary considerably with

the wind during summer conditions when the windows were open.

The data in Table 4 and Fig. 6 show that the high rate of air

exchange between patient rooms and the corridor cause the concentration of air-borne contaminants to be nearly as high in the corridor

as in the adjoining rooms during winter conditions. The contaminants in the corridor would be carried toward the main part of the

VENTILATION PATTERN UNDER SUMMER CONDITIONS

\

j=

=n

\\

\Y

- 18 -

hospital to the several air exhaust openings In service rooms,

etc. Reduction of the concent ration in the corridors or in the

corridors and patient rooms could be accomplished in three ways,

(l) by dilution with fresh air, ( 2 ) by isolating the contaminants

in the patient rooms where they originate, or ( 3 ) by using germicidal means in the corridors or in the rooms or both to destroy

the contaminants.

The dilution method has been widely used in tuberculosis

hospitals in the past. The possibilities of dilution with fresh

air are illustrated, in principle, by the earlier analysis of

the winter and summer air exchanges, shown in Fig. 6 and Fig. 7 . However, very large quantities of heat would be needed to warm

the necessary fresh air during winter conditions and, if comfort

were desired in the summer time, very large air conditioning

equipment would be required.

The contamination in the corridors could be materially reduced, if not eliminated, by keeping the doors to the patient

rooms closed, except during entry, and maintaining a slight positive pressure in the corridor. However, this would cause the level

of contamination in the patient rooms to rise significantly unless

the air exchange through the windows was increased by a factor of

ten or more which would again significantly increase the heat

requirements. If the window leakage was not increased the nurses

and hospital staff would be subjected to the higher concentration

of contamination for the periods of time they spent in the patients’

rooms

.

High efficiency air filters, ultraviolet radiation, glycol

vaporizers, and lithium chloride brine dehumidifiers have all been

used to reduce the pathogenic microorganisms in an air stream

either by killing them or filtering them out of the air. The

relative merit of these different types of equipment has not been

established. However, a proposed pilot installation of germicidal lamps was discussed with the research medical staff at the

Lochraven Hospital that would coordinate the germicidal function

of the lamps with the observed pattern of air movement between

the patient rooms and corridor in Ward 4-B. This arrangement involved placing the lamps above a grating in the corridor over the

doorway and opposite an opening in the wall of the room over the

doorway in a location that would irradiate all of the air passing

through the doorway and also direct ultraviolet radiation into the

room in the zone between eye level and the ceiling. A grating in

-19-

the opening over the doorway prevented seeing the source of radiation from anywhere in the room and the overhead grating in the

corridor prevented seeing the source of radiation, except from

directly beneath the lamp. Air exchanged between the patient rooms

and corridor would pass through the radiation zone whether the poqjp

was cooler or warmer than the corridor.

This proposal was further developed by the research staff at

the hospital and a pilot installation is being made in Wing 4-B

to determine the effectiveness of the system in controlling the

spread of living microorganisms. When the installation is completed, further measurements of the air flow patterns over the

germicidal lamps and in the patient rooms will be made.

USCOMM-NBS-DC
.

*
U.S. DEPARTMENT OF COMMERCE

tr.-.l.ii.k II. MurlliT. S.-.ntury NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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