3 4 A S H R A E J o u r n a l a s h r a e . o r g F e b r u a r y 2 0 0 3

ROOMFOR CRITICAL ENVIRONMENTS

n HVAC design area that has not yet developed a standard “rule-of-thumb” is the quantitative determination of differential pressure

and airflow for “proper” room pressurization. This article investigatescurrent design guidelines and field practices for room pressurization.In particular, the author explores current literature that addresses thedefinition of “proper” pressurization.

The article then examines some prac-tical in-field design considerations fortwo types of facilities, a tuberculosisBSL-3 research lab and a health-carehematopoietic stem cell transplant unit.In addition to field tests, the author pro-vides a methodology for practitioners forverifying airflow direction, into or out ofthe room. The author concludes with rec-ommended guidelines or “rules-of-thumb” values that may be a usefulreference in designing rooms that requirea proper negative or positive pressure.

Review of Literature and GuidelinesChapter 12 in the 2001 ASHRAE Hand-

book — Fundamentals provides a good

treatise on air contaminants. Commonroom contaminants to be contained in-clude airborne/aerosolized infectiousdiseases in hospitals and vivariums;chemical and biological spills in labora-tories; and explosive dusts in manufac-turing facilities.

Common rooms that strive to excludecontaminants include protective isola-tion rooms in hospitals for immuno-compromised patients; clean rooms forindustrial and pharmaceutical manufac-turing; barrier rooms for nude mice invivariums; and food-processing rooms ina food supply facility. The method toachieve directional airflow is via the con-trol of the supply and exhaust airflows

within and adjacent to the concernedroom.

The salient question is how much thedifferential airflow should be to achieve“proper” room pressurization/directionalairflow? This leads to the prerequisitequestion: What is “proper” pressuriza-tion/directional airflow?

Room Pressurization FundamentalsRoom Pressurization FundamentalsRoom Pressurization FundamentalsRoom Pressurization FundamentalsRoom Pressurization Fundamentals

Room pressurization depends on theability of air to build up within a room.The leakage into or out of room is a keyfactor. Chapter 26 of the 2001 ASHRAEHandbook—Fundamentals presents aleakage function relationship that corre-lates a room or building envelope air leak-age to the differential pressure producingthe flow.

ASHRAE defines the leakage functionwith the presentation of the “power lawequation” (Equation 32) as:

( )nPcQ ∆=

About the Author

Brian Wiseman, P.E., is president of AirflowDirection Inc., Saugus, Mass.

AAAAABy Brian Wiseman, P.E., Member ASHRAE

PRESSURE

Copyright 2003, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permissionfrom ASHRAE Journal, February 2003. This article may not be copied nor distributed in either paper or digital form without ASHRAE’s permission.

F e b r u a r y 2 0 0 3 A S H R A E J o u r n a l 3 5

Room Pressurization

where Q is the volumetric rate of flow through an orifice. Cis a flow coefficient that depends on the geometry of the ori-fice. C is empirically determined using a fan pressurizationtest, similar to the duct leakage test performed by air balanc-ers. ∆P is the pressure differential across the orifice and n is thepressure exponent, commonly around 0.65 per ASHRAE. Fig-ure 1 shows the characteristic “infiltration curve” that repre-sents the power law equation. Thus, if the gaps around a closeddoor and gaps to adjacent spaces are modeled as an orifice andyou know: a) the differential pressure you want to obtain, b)the geometric coefficient of the gaps, and c), the empiricalexponent n, you can calculate the differential airflow. How-ever, what is the required differential pressure and related dif-ferential airflow to “properly” contain or keep outcontaminants?

Recommended Differential PressureRecommended Differential PressureRecommended Differential PressureRecommended Differential PressureRecommended Differential Pressure

The Centers for Disease Control’s “Guidelines for Prevent-ing the Transmission of Mycobacterium Tuberculosis in Health-Care Facilities” states a minimum differential pressure ∆P of0.001 in. w.c. (0.249 Pa) is required to achieve a directionalairflow into or out of a room.However, this value is chal-lenged as insufficient basedon potential thermal stratifi-cation in a room, room sup-ply air diffusion and, as thisarticle will show, door swingsand eddies.

Chapter 15, Clean Spaces,in the 1999 ASHRAE Hand-book — HVAC Applications,states a differential room tocorridor pressure ∆P of 0.05in. w.c. (12.45 Pa) is consid-ered to be a widely used stan-dard.

The American Institute ofArchitects’ “Guidelines forthe Design and Constructionof Hospital and Health CareFacilities” states a minimum ∆P of 0.01 in. w.c. (2.49 Pa) differ-ential is required.

When Ahmed, Mitchell and Klein1 simulated a model of thedynamics of laboratory pressurization, they used a ∆P of 0.05in. w.c. (12.45 Pa) based on three references in their article.

Burns and Milburn2 researched regulatory authority for re-quired differential pressures for biological facilities. Theyfound no quantitative values of pressure in the Federal Stan-dard 209C through E (currently cancelled and replaced withISO 14644) and current good manufacturing practices (GCMPs)defined in federal regulations 21 CFR, parts 210 and 211 (Fed-

eral Register 1995). Burns and Milburn did find a 1987 U.S.Food and Drug Administration publication that stated a ∆P of0.05 in. w.c. (12.45 Pa) is acceptable.

Recommended Differential AirflowRecommended Differential AirflowRecommended Differential AirflowRecommended Differential AirflowRecommended Differential Airflow

Aside from the previous references, the author made otherinitial searches of quantitative references on room pressur-ization/directional airflows. The search includedANSI/ASHRAE Standard 62-2001, Ventilation for Accept-able Indoor Air Quality; the 1999 ASHRAE Handbook—HVACApplications, Health Care Facilities; and the National Re-search Council’s “Prudent Practices in the Laboratory,” RoomPressure Control Systems. Each of these references providesa good qualitative description of room pressurization. Par-ticular attention is drawn to the ASHRAE Handbook, wherethe qualitative pressure relationship of many types of roomsare detailed and act as a good reference. However, a quantita-tive guide was not found for differential airflows to achieveroom pressurization/directional airflow.

The American Conference of Governmental Industrial Hy-gienists (ACGIH) Industrial Ventilation, A Manual of Recom-

mended Practice addresses aquantitative design differen-tial airflow. It states “theproper flow differential willdepend on the physical con-dition of the area, but a gen-eral guideline would be to seta 5% flow difference but noless than 50 cfm (24 L/s)”(emphasis added).

The American IndustrialHygiene Association (AIHA)publication “Clarificationsof ANSI/AIHA Z9.5 Standardfor Laboratory Ventilationtakes a position that controlsusing room differential air-flow setpoints are preferredover controls that use roomdifferential pressure. The text

suggests a 10% offset between the supply and exhaust airflowsand notes this value has no general validity. The text focuseson the containment or exclusion requirements of an open doorversus a closed door and the effect on the overall differentialairflow to obtain a 50 fpm (0.254 m/s) velocity through anopen door.

The text suggests and rightly so, that an open door designcriteria is impractical considering a 3 ft (0.9 m) × 7 ft (2.13 m)door would yield 1,050 cfm (495 L/s) makeup air through thedoor. Often, most communicating corridors are egress corri-dors and for smoke control purposes, most building codes pro-

Inside of a positive pressure isolation room.

3 6 A S H R A E J o u r n a l a s h r a e . o r g F e b r u a r y 2 0 0 3

hibit the communicating corridor from providing any signifi-cant transfer air to the adjacent rooms. Therefore, the high airvolume required to contain or keep out contaminants throughan open door would violate the code.

The text suggests the use of an airlock for critical applica-tions, thereby obviating the potential for a continuous opendoor path from the room to the communication corridor. Asseen later in this article, an airlock or anteroom is a good idea.

A National Institutes of Health (NIH) publication, ResearchLaboratory Design Policy and Guidelines, recommends a mini-mum of 94 cfm (44 L/s) of negative makeup air per lab moduleto adjacent non-lab spaces.

So far, in search of a design differential airflow to put onthe drawings, it seems that a 5% to 10% differential cfm is anaccepted guide. However, what about the air balancer whohas a 5% to10% balancing tolerance? Is a design airflowdifferential of 5% to 10%enough? In a typical health-careinfectious isolation room, a mini-mum of 12 total air changes perhour (all air exhausted out of theroom) is recommended in theAIA/HHS “Guidelines for Designand Construction of Hospital andHealth Care Facilities.” A typical12 ft (3.66 m) × 12 ft (3.66 m)room by 8 ft (2.44 m) ceilingwould have 230 cfm (109 L/s) ofexhaust air. At 10% differential,the supply air would be a maxi-mum of 207 cfm (98 L/s). The airbalancer could set the supply to228 cfm (108 L/s) and the exhaustto 207 cfm (98 L/s) and the roomwould be positive. The projectspecifications, of course, mustdictate a +0%/–10% for the sup-ply and +10%/–0% for the ex-haust. But is 23 cfm (11 L/s) ofmakeup air enough for a 12 ft (3.66 m) × 12 ft (3.66 m) infec-tious isolation room?

Review of Applied PracticesDifferential Airflows and PressuresDifferential Airflows and PressuresDifferential Airflows and PressuresDifferential Airflows and PressuresDifferential Airflows and Pressures

Ahmed, et al.1 applied ASHRAE’s power law equation intheir modeling analysis of the dynamics of laboratory pres-surization. Ahmed also calculated a typical leakage value forK =1,000, which Ahmed finds represents a moderately tightenvelope. Ahmed found for a typical laboratory module of30 ft (9.14 m) × 25 ft (7.62 m) by 10 ft (3.05 m) ceiling,maintaining 0.05 in. w.c. (12.45 Pa), a K value =1,000, thedifferential airflow theoretically should be 153 cfm (72 L/s)

through the closed door gaps leading into the room. Coogan3

applied the same modeling approach as Ahmed and foundthat the infiltration curve described in ASHRAE is a goodapproach. Values between 150 cfm (71 L/s) and 300 cfm (142L/s) were found to “properly” achieve a negative pressurerelative to the adjacent rooms.

Dale Hitchings4 offers the equation: Offset design

= 2 ε S Fmax

where the offset is the differential airflow cfm, ε is the instru-ment error for measuring the airflows (typically 5%), S is asafety factor between 0.5 and 2.0 (typically 1.1) and F is themaximum designed supply or exhaust flow rate. For a lab ex-hausting 5,000 cfm (2360 L/s), the offset would be 550 cfm(260 L/s). The author finds that in a typical 500 ft2 (46.45 m2)lab module with one door and a 1,000 cfm (472 L/s) fumehood exhaust, the transfer would equate to about 110 cfm (52L/s) through the door to the lab.

Kenneth Gill5 has found that 75cfm (35 L/s) to 100 cfm (47 L/s)makeup air through one door to anegative healthcare patient isola-tion room works well. This rangeallows 100 fpm (0.508 m/s) mini-mum through typical openingssuch as the door undercut. Gill6

further finds in an application forjail TB isolation rooms that 130cfm (61 L/s) of transfer air throughthe door undercut worked well andprovided 0.05 in. w.c. (12.45 Pa)differential pressure with the singledoor to the room closed.

Gaslon and Guisbond7 presentsubstantive information on roomventilation and air change ratesfor sepsis control in a health-caresetting. Regarding any differen-tial pressures or airflows, Gaslonrefers to the previously mentioned1994 CDC guideline differential

pressure value of 0.001 in. w.c. (0.249 Pa).Andrew Streifel8 has published a preferred minimum differ-

ential cfm of 125 cfm (59 L/s) for a sealed positive or negativeisolation room as well as a minimum of 0.01 in. w.c. (2.49 Pa)and an ideal differential pressure of 0.03 in. w.c. (7.47 Pa).Streifel bases this on a room with about 0.5 ft2 (0.047 m2) ofleakage and 12 ACH.

Room Door SwingRoom Door SwingRoom Door SwingRoom Door SwingRoom Door Swing

Sansone and Keimig9 state that swinging doors should openin the same direction of airflow. Sansone and Keimig base theirconclusion on eddies that travel around the edge of a travelingdoor, from higher pressure to lower pressure. If the door travel

–100

–200

–300

–400

–500

Infiltration Flow (cfm)

500

400

300

200

100

–0.1

–0.0

8

–0.0

6

–0.0

4

–0.0

2

0.02

0.04

0.06

0.08

0.1

Pressure Drop (in. w.c.)

Figure 1: Infiltration curve (power law equation).

Room Pressurization

F e b r u a r y 2 0 0 3 A S H R A E J o u r n a l 3 7

creates a high pressure on the leading side of the door, then tominimize eddies, the pressure on the leading side should be asless as possible. Thus, a door opening into a negative room isbetter than opening into a positive room. The author’s find-ings differ from this conclusion. The smoke tests describedlater, indicate the room is transiently pressurized or depressur-ized, depending on the direction of door swing. Once the dooris opened more than a foot, the anteroom or corridor is virtu-ally the same pressure as the concerned room. Therefore, anycontaminants that were pushed out of a negative room withthe door opening into it would remain in the anteroom or worse,the corridor.

Sansone and Keimig found that increased door swing ve-locities affect the containment or exclusion of contaminantsin a room and recommend slowdoor opening and closing. Ourfindings described below agreewith this. The traveling speedcontrol can be accomplishedwith an adjustable, off-the-shelfdampened door closure.

Real-World ExperienceThe author’s experience is in

design and testing of HVAC sys-tems for health-care and labora-tory facilities, with particularattention towards proper airflowdirections, into or out of rooms.Tests were performed for roompressure vs. differential airflowin two types of facilities, ahealth-care hematopoietic stemcell transplant unit and a tuber-culosis BSL-3 research lab. Inaddition to the quantitative testresults, the tests present a meth-odology for practitioners for verifying the airflow directioninto or out of the room.

Room Pressure for ContainmentRoom Pressure for ContainmentRoom Pressure for ContainmentRoom Pressure for ContainmentRoom Pressure for Containment

To determine a minimum practical containment pressure,we performed tests on two, ±200 ft2 (18.58 m2) tuberculosisbiosafety level 3 research lab rooms. The wall, floors and allpenetrations were sealed, including the electrical conduitswhere they met the boxes. The windows were inoperable. Thelight fixtures were surface mounted. There was one door enter-ing into each of the BSL-3 rooms. The doorjambs were notsealed and there was a 0.5 in. (12.7 mm) door undercut.

Because aerosolized TB containment was so critical, wespecified and installed an airflow direction indicator10 as shownin Figure 2.

The indicator’s translucent tube penetrates the wall with aslight incline up into the room. The sphere inside the tube rollsin the direction of airflow. When the door is closed and there isproper negative room pressure, the sphere is sucked into theroom, up the tube’s incline and the sphere can be seen insidethe room. When the room door is open, the tube’s incline rollsthe sphere out into the anteroom and thus provides a self-check feature, each time the door is opened.

For the first BSL-3 room tested, we set up the differentialairflow corresponding to a 10% differential. The indicator sphereproperly rolled into the room with the door closed. For thisroom, the door swung into the room. When the door was opened,the sphere was rapidly pushed out into the vestibule. The indi-cator sphere was to roll out of the room slowly, down the tube’s

incline. The investigators sus-pected the room was tran-siently under positive pressure.We performed a smoke test towatch the eddies around thetop and latch side edges of thedoor. When we opened thedoor, the smoke trailed thedoor travel and portions of thesmoke in the door’s wake werepushed out of the room. Thetrail of smoke can be seen inFigure 3.

The airflow direction indi-cator was sensitive and visualin showing the transient rever-sal of airflow direction throughthe doorway. We performed thesame test with the door clos-ing and the room went furthernegative. With the negativecondition, the smoke was con-tained and therefore the clos-

ing of a door that swings into a negative room has no detriment.We proceeded to perform the transient door test on another

BSL-3 negative pressure room where the door opened out intothe corridor. When the door was opened, the eddy smoke trailsfollowed the door in the beginning of the door travel, but thesmoke was sucked back into the room as shown in Figure 4.

The next set of tests explored the capture velocity of a par-tially opened door as a function of room differential pressure.The tests were done on the first BSL-3 lab room. The differentialpressure was set with the door closed, using a micromanometer.The door was opened and held partially open to observe thetrail of the smoke plume in the plane of the door. Figure 5 showsthe smoke plume not being captured at 0.001 in. w.c. (0.249 Pa).Figure 6 shows the plume being about to be captured at 0.003in. w.c. (0.747 Pa). The capture significantly improved at a dif-

Figure 2 (left): Airflow direction indicator. Figure 3 (right):Indicator above door that is opening into negative room,smoke is not contained.

Figure 4 (left): Door opening out of positive room, smoke iscontained. Figure 5 (right): Smoke plume is not captured ata negative room ∆∆∆∆∆P of 0.001 in. w.c. (0.249 Pa). Arrow pointsto leading edge of plume.

3 8 A S H R A E J o u r n a l a s h r a e . o r g F e b r u a r y 2 0 0 3

ferential pressure of 0.008 in. w.c. (1.992 Pa), shown in Figure 7.The purpose of this test was to challenge the 0.001 in. w.c. (0.249Pa) stated in the CDC guidelines mentioned earlier. We recog-nize that people walking through the doorway will cause distur-bances and thus an anteroom is a good idea.

Regarding the differential airflow required to obtain 0.015in. w.c. (3.735 Pa) in the above BSL-3 rooms, the airflow differ-ential was equal to about 150 cfm (71 L/s) differential, of whichwas made up through the 0.5 in. (12.7 mm) door undercut.

Room Pressure for a Protective EnvironmentRoom Pressure for a Protective EnvironmentRoom Pressure for a Protective EnvironmentRoom Pressure for a Protective EnvironmentRoom Pressure for a Protective Environment

The next test performed was on a health-care stem cell trans-plant positive pressure isolation room (±200 ft2 [18.58 m2]).The elevator lobby/entry airlock leads to the suite of isolationrooms. The airlock protects the suite against building pressurefluctuations caused by the elevator shafts. The entry door was4 ft (1.2 m) wide with top and side seals and a 0.75 in. (19 mm)nominal undercut.

The photo on Page 35 shows the inside the room where onthe left, was a bathroom with a separate door that had side andtop seals but no bottom seal (good for air change rate). The 2 ft(0.61 m) x 2 ft (0.61 m) fluorescent lights were recessed solidacrylic lense and the windows were non-operable. The ceilingwas gasketed lay-in tile frame. The high-hat light fixtures wereheat-removal type of which were changed after the test to fix-tures with lenses.

The walls and floor penetrations were sealed to best of gen-eral construction standards that can be from excellent to suffi-cient. Two access panels, later sealed, penetrated thecorridor-to-room wall above the ceiling. The toilet exhaustwas common to other toilet exhausts. A special sink in thepatient room (not bathroom) had an open gap drain to anotherspace below (no P-trap) for sanitation purposes.

The room supply was via a pressure independent primary airHEPA filtered fan-powered series box. The return to the fan-pow-ered box was in the room. The house exhaust for the room wasserved by a pressure independent exhaust box. The supply andexhaust airflows were measured with an air volume hood. Thedifferential pressures were measured by placing the static probein the middle of the room, routing the tube through the doorundercut and connecting the probe to the digital manometer out-side the room. An airflow direction indicator was placed above theentry door to show when the room was under positive pressure.

We conducted various airflow versus differential pressuretests on the room. Table 1 summarizes the tests in two states:the entry door to the positive pressure isolation room com-pletely sealed and then with the undercut to the entry door notsealed. The bathroom/toilet exhaust and the house exhaustwere not physically altered but they slightly responded to theroom pressure changes caused by our alterations of the pri-mary air supply to the room.

After performing the above tests on the positive pressureisolation room, we conducted tests on the remaining isolationrooms to determine the differential airflow to obtain a mini-mum 0.01 in. w.c. (2.49 Pa). The differential airflow rangedfrom 150 cfm (71 L/s) to 400 cfm (189 L/s).

Based on this empirical experience, we arrived at a roomdifferential airflow at 300 cfm (142 L/s) for rooms of this con-struction and with door seals all-around, 400 cfm (189 L/s)with no door bottom seal with a closed bathroom door.

Door Swings and AnteroomsDoor Swings and AnteroomsDoor Swings and AnteroomsDoor Swings and AnteroomsDoor Swings and Anterooms

Based on the BSL-3 lab test observations of door swingeffect on room pressure, we recommend for a negative orpositive pressure room that the entry doors be gasketed, slid-ing break-away doors. If a standard swing door is used, werecommend it swing out of the room for a negative room andswing into the room for a positive room. This may not alwaysbe practical. For example, hospital isolation room doors thatare located off the main corridor cannot swing out into thecorridor. In such cases, we advise a room be found that canincorporate an anteroom.

An airlock (anteroom) should be used whenever possible.The anteroom “traps” any escaped air from a negative roomand isolates corridor air from a positive room. Because theanteroom is a trap, it should incorporate a high air change rateof around 12 ACH or higher and the differential cfm should bezero or neutral to allow overall desired directional airflow be-tween the corridor and the concerned room.

Figure 6: Smoke plume starting to be captured at a roomdifferential pressure of 0.003 in. w.c. (0.747 Pa). Arrow pointsto leading edge of plume.

Figure 7: Smoke plume showing definite capture at a roomdifferential pressure of 0.008 in. w.c. (1.992 Pa). Arrow pointsto leading edge of plume.

Room Pressurization

F e b r u a r y 2 0 0 3 A S H R A E J o u r n a l 3 9

Conclusion and SummaryBased on the tests on the three rooms, some

basic points for designing for proper room pres-surization based on differential airflow settingsinclude: seal the room, meet or exceed mini-mum codes for air change rates, incorporate in-dustry regulations and practice for minimumair change rates and room pressure. However, asa minimum, strive for 0.01 in. w.c. (2.49 Pa) to0.05 in. w.c. (12.45 Pa) differential pressure andconsider an initial 400 cfm (189 L/s) room dif-ferential capacity with throttling capability.

When designing the HVAC system to obtainthe desired room pressurization/directional air-flow for ±200 ft2 (18.58 m2) rooms, considerthese points (this article is not intended to sub-stitute for an HVAC design by a registered, li-censed professional engineer):

• Rooms should have a minimum negative orpositive pressure of 0.01 in. w.c. (2.49 Pa) where0.05 in. w.c. (12.45 Pa) or higher is preferred.Codes and industry regulations and practicemay dictate specific limits.

• Rooms should have a differential airflow to obtain the 0.01in. w.c. (2.49 Pa) or higher. For ±200 ft2 (18.58 m2) rooms, thebest approach is to have the differential capability of 400 cfm(189 L/s) and the ability to throttle down the differential tosatisfy the 0.01 in. w.c. (2.49 Pa) or higher. For 0.01 in. w.c.(2.49 Pa), the author has seen 400 cfm (189 L/s) of differentialairflow for a room thought to be well sealed. Another roomrequired only 150 cfm (71 L/s) of differential airflow. The rangedepends on ceiling, wall and window tightness, door seals andthe existence of other supply or exhausts in the room.

• Air balancer specs for positive rooms should be(+10%/–0%) for supply, (+0%/–10%) for exhaust. Negative roomsshould be (+10%/–0%) for exhaust, (+0%/–10%) for supply.

• For negative rooms, the makeup air should be provided viaa supply outside the room. For positive rooms, exfiltration ofair should be accommodated by an exhaust outside the room.

• All room penetrations above and below the ceiling and theductwork should be well sealed.

• The ceiling should be tight as possible, preferably sheetrockor concrete deck.

• Specify surface mount or recessed vapor-tight, or non-re-turn-air light fixtures.

• Each entry door to the room should be sealed on its top andsides (including astragal vertical joint seal for leaf or doubledoors) and include an adjustable bottom seal.

• A sliding entry door is preferred over a swing door. If aswing door is used, it should open out of a negative room oropen into a positive room.

• Anterooms should be used whenever possible with 12 airchanges per hour (ACH) minimum (codes and industry regula-

tions and practice may dictate higher values) and a neutral pres-sure where the supply and exhaust airflow quantities are equal.

• An airflow direction indicator should be installed to visu-ally see the dynamics of the room pressurization.

References1. Ahmed, O., et al. 1993. “Dynamics of laboratory pressur-

ization.” ASHRAE Transactions 99(2):223–229.2. Burns, J.T. and W.F. Milburn. 1999. “Specification and

performance of testing and balancing in biologics facilities.”ASHRAE Transactions.

3. Coogan, J.J. 1996. “Effects of surrounding spaces on roomspressurized by differential flow control.” ASHRAE Transactions102(1):18–25.

4. Hitchings, D.T. 1994. “Laboratory space pressurizationcontrol systems.” ASHRAE Journal. 36(2):36–40.

5. Gill, K.E. 1994. “HVAC design for isolation rooms.” Heat-ing/Piping/Air Conditioning. February, pg. 45.

6. Gill, K.E. 1997. “Tuberculosis isolation room design us-ing CDC guidelines.” Heating/Piping/Air Conditioning.September, pg. 69.

7. Galson, E.L. and J. Guisbond. 1995. “Hospital sepsis con-trol and TB transmission.” ASHRAE Journal, 37(5):48–52.

8. Streifel A J. 2000. “Health-care IAQ: guidance for infectioncontrol.” Heating/Piping/Air Conditioning. October, pg. 28.

9. Sansone E.B. and S.D. Keimig. 1987. “The influence ofdoor swing and door velocity on the effectiveness of direc-tional airflow.” ASHRAE IAQ ’87. May, pg. 372–381.

10. Airflow Direction Inc. ADI Indicator is protected underone or more U.S. Patents U.S. [5,291,182], [5,410,298],[5,798,697] [5,661,461] and Canada Patent [2,107,396].

Table 1: Delta-cfm vs. Delta-P for positive pressure isolation room withbathroom inside isolation room.

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)25(011 )04(58 )29(591 )432(594 )241(003 )94.2(010.0+

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)25(011 )04(08 )09(091 )632(005 )641(0135400.0+)121.1(

)24(09 )24(09 )58(081 )703(056 )222(074 )47.3(510.0+