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FEBRUARY 20U

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HEATING/PIPING/AIR CONDITIONING

EGB: Benefits of Whole-Building Design Utilizing Plant Effluent for Heating and Cooling

ENGINEERING

Excerpt from the book "The Ecological Engineer: Glumac": Kelley Engineering Center

Design of a Specialized

Airborne-Infection­ Isolation Suite

Lessons learned from the design of new National Institutes of Health facility By fARHAD MEMARZADEH, PhD, PE,

and DEBORAH E. WILSON, DrPH, CBSP,

National Institutes of Health,

Bethesda, Md.,

and KRISHNAN RAMESH, PE,

Affiliated Engineers Inc.,

Rockville, Md.

ria used for the SCSU, which can be applied for any other type of alrborne-infection-isolation suite (AIlS). General Design Features The SCSU receives air via the main clinical supply-air system, wruch is served by air-handling units located in another part of the building. Trus is a manifolded system providing supply air to all patient rooms and support spaces (Figure 1). All clinical spaces are served by a non-recirculating (100-percent exhaust) HVAC system. All general clinical spaces, as welJ as the adjacent Vaccine Evaluation Clinic (VEC), are served by general exhaust systems consisting of multiple exhaust fans connected to a common exhaust­ air manifold. Dedicated isolation-room exhaust systems consist of multiple exhaust fans connected to a common exhaust-air manifold. If one fan fails, the remaining fans

A b iocbntainment patient-care unit (BPCU) is a facil­ ity designed and operated to maximize patient care with app opriate infection-control practices and procedures. A PCU is secure, is physically separated from other patient-care areas, and has special air-handling systems. 1 The National Institutes of Health's Speclll Clinical Studies Un" (SCSU) Vaccine Evaluallon Clinic new Special Clinical Studies Unit (SCSU) (Illcludes occupallonal~xposure Isolation room, patient room, and nursing support) in Bethesda, Md., is a rughJy specialized BPCU, housing patients with extremely infectious diseases transmissible by respiratory aerosolization, direct con­ tact with primary body fluids, or dried infectious particles from body fluids. The SCSU has three patient rooms plus an occupational-exposure isola­ tion room (OETR).1t is equipped to meet all clinical-care needs, including basic medical observation, minor surgical procedures, and intensive care. Thus, planning had to address housekeeping, • Welded stainless-s18e1 ductwork security, emergency evacuation, and the use of experimental therapeutics. T1Us article will discuss design crite- FIGURE 1. a...t .....ment of mechanical systems.

Director of the National Institutes of Health's (NIH's) Division of Technical Resources, Farhad Memarzadeh, PhD, PE, consults on matters related to biocontainment and medical research laboratories around the world. He has written four books and more than 60 scientific research and technical papers pubJ.ished in peer-reviewed journals and been a guest and keynote speaker for more than 50 international scientific and engineering conferences and symposia. Deborah E. Wilson, DrPH, CBSP, is director of the NIH's Division of Occupational Health and Safety and founder and director of the National Biosafety and Biocontain­ ment Training Program. She is a career U.S. Public Health Service Commissioned Officer. Krishnan Ramesh, PE, is a managing prindpal of Affiliated Engineers Inc. He has extensive experience planning, engineering, and designing biological and chemical research laboratories and vivaria nationwide and is a technical contributor to the NIH Design Requirements Manual for Biomedical Laboratories and Animal Research Facilities. 24

I8ta\C &NGINDRING

FEBRUARY 2011

compensate to provide the required design exhaust-air quantity. The VEe is exhausted through the general clinical exhaust system, while the sesu is exhausted through a dedicated system. Exhaust air from all sesu spaces, including the OEIR, is manifolded in the dedicated exhaust system. The dedicated system is equipped with high-efficiency-particulate-air (HEPA) filters prior to exhaust fans and discharges outside (Figure 2). At both entrances to the sesu are vestibules maintained at negative pressure relative to the adjoining corridors. The OEIR has an ante­ room maintained at negative pres­ sure relative to the rest of the sesu to mitigate the risk of release of an airborne agent. The negative pres­ sure of the patient rooms, the OEIR, and the sesu is monitored and alarmed at the nurses' station.

Vaccine Evaluation Clinic

Special Clinical Studies Un" (SCSU)

• Welded stainless-steel ductwork

Hlgll-efficiency-particulate·alr filtration unij

AGURE 2. Dual-use-Isolation-roocn Interoollillechlnlcil syste....

SCSU Design Features Design features specific to the sesu include: .. Walls (outside of the OEIH) sealed to minimize uncontrolled

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Circle 168 FEBRUARY 2011

NPAC ENGINEERING

25

DESIGN OF A SPECIALIZED AIRBORNE-INFECTION-ISOLATION SUITE

Galvanlzed·steel ductwork Welded stainless-steel ductwork •

Best fuel efficiency of any firetube

AGURE 3. Dual-use Isolation room.

Completely integrated • Self-closing exit doors. • Balanced ventilation air to main­ tain negative pressure (inflow of air) relative to the corridor (between public corridor and the SCSU). • Exhaust-air grilles located low on patient-room walJs. • Pressure-monitoring system continuously indicating airflow from adjacent spaces into the SCSU. • Displays of relative space pres­ surization at the corridor and vesti­ buJes. • Remote alarms at the nurses' station. • Twelve-air-changes-per-hour (ACH) minimum ventilation rate of non-recirculating air (100-percent outdoor air) for the SCSU and OEIR. • Dedicated toilet, bath, and hand­ washing facilities in each patient room. • Dedicated exha ust-air system serving the SCSU and OEm. The dedicated constant-volume exhaust system consists of three vari­ able-speed exhaust fans. Each fan is designed at 50 percent of capacity to provide the required level of redun­ dancy and reliability and 20-percent reserve-airflow capacity to account for final air-balance adjustments and future needs. The fans operate con­ tinuously, their speed controlled with variable-frequency drives based on a

static-pressure sensor in the exhaust ductwork. Discharge from the fans is manifolded to ensure a high stack­ discharge velocity. One of the exhaust fans receives life-safety branch power; the other two receive general standby-equip­ ment branch power. In the event of normal power loss, life-safety power is restored within 10 sec, and the first fan is re-engaged and ramps up to satisfy required minimum exhaust and directional airflows. Shortly thereafter, power to the other fans is restored, and the fans arere-engaged . Air distribution to individual spaces! rooms is by constant- and/or vari­ able-volume, pressure-independent supply and exhaust air terminals to each temperature- and/or pressure­ control zone. Pairs of supply and ex­ haust venturi-style air-term.inal units track airflow to ensure the specified pressurization (directional airflow) is maintained. The onJy prerequisite for the air terminals to operate properly is sufficient duct static pressure. Th.is is monitored via differential-pressure switches across each air valve. Addi­ tionally, automatic bubble-tight iso­ lation dampers are provided in the supply duct to each zone. AU exhaust air-terminal units are low-leakage (less than 3 cfm at 1 in. water), with high-speed actuators

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Minimum excess air across the operating range

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Circle 170 FEBRUARY 2011

HPAC ENGINDRING

27

DESIGN OF A SPECIALIZED AIRBORNE-INFECTION-ISOLATION SUITE

(Iess-than-1-sec fulJ response time) to stay within 5 percent of airflow set point. The air-terminal units' controllers are linked between supply and exhaust. If duct static pressure falls below levels required for accurate tracking, the supply-air bubble-tight dampers close, and the exhaust-air valves are commanded to a minimum position, maintaining directional airflow. The control devices operate autonomously, even in the event communications with the overall building control system are dis­ rupted. All of the contro.llers and bubble-tight dampers are provided uninterruptible power to ensure the air-terminal units track each other to maintain the specified airflow differential. All serviceable compo­ nents, such as air terminals, exhaust valves, and reheat coils, are located in the interstitial space outside of the patient-care/containment area. AU exhaust ductwork for the SCSU and negative-pressure examination room on the room side of the HEPA filter is made of welded stainless steel (Figure 3). The supply ductwork is made of galvanized steel augmented with welded stainless steel. Bubble­ tight dampers are provided on all supply ducts branching from the interstitial level to SCSU patient rooms and the OEIR. These are fast-acting pneumatic actuators that close upon a loss of exhaust airflow. Ductwork from the bubble­ tight dampers to air devices is made of welded stainless steel. Backflow preventers are installed in domestic-water piping running to the SCSU. When the SCSU is in isola­ tion mode, oxygen, medical vacuum, and medical air are provided via local dedicated units . HEPA filtration is provided on the main plumbing vents leaving the SCSU. Emergency power is provided for critical branch, life-safety, and standby equipment in the SCSU and for exhaust fans on the interstitial level as appropriate. Electrical services for the OEIR 28

HPAC ENGINEERING

FEBRUARY 2011

are sealed airtight to mInimize outside penetrations. A third in­ ner layer of sheetrock prevents air migration that can occur as the result of required utility boxes and

associated penetrations_

Room Control Sequences Under normal conditions, sup­ ply- and exhaust-air valves oper­

•

Air·handllng units, N+ 1 redundancy

Two exhaust fans on emergency power ---"--1-;:;:"'[ One exhaust fan on life-safety power ----1-.:;;;1'1 Main-building clinical exhaust

+------".

Exhaust air to main building

Exhaust air to SCSU exhaust fans Supply air from main building

SUppiy air from G:D-----'~---... main building

Vaccine Evaluatloll Clinic

Special Clinical Studies Unit (SCSU) Occupational-exposure Isolation room

RGURE 4. ManHolded supply-air syste", and dedicated exhaust-air system for the SCSU.

Air-handling units. N+1 redundancy

I I~

•

Two exhaust fans on emergency --""---l~'"

power

One exhaust fan on life-safety power - - - - 1 ' 771 Main-building clinical exhaust + - - - - , Exhaust air to SCSU exhaust fans Supply air from main buUding

Exhaust air to main building

Supply air from main building

...

_~_

GIi.-,---.. . ·• •

Vaccine EvalllUon Clinic

Exhaust air to SCSU exhaust fans

.--0( +-­ _

Supply air from main building

Occupatlonal-exposure Isolation room (OEIR)

OEIR airteroom

Special Clinical Stadles Unit (SCSU) RGURE 5. ManHolded supply-air system and dedicated exhaust-air system for the SCSU.

DESIGN OF A SPECIALIZED AIRBORNE-INFECTION-ISOLATION SUITE

ate at "constant" airflow set points. The fixed differential between sup­ ply- and exhaust-airflow set points provides directional airflow and room pressurization_ For example, an exhaust-airflow set point of 700 cfm and supply-airflow set point of 600 cfm provides tOO-cfm inward airflow, maintaining a room at negative pressure. As long as the "measured" differential pressure across the supply- and exhaust-air valves is within an acceptable range (0.6 in. wg to 3.0 in. wg), air valves maintain their respective constant­ airflow set points, maintaining direc­ tional airflow and room pressuriza­ tion. Differential-pressure switches across each supply- and exhaust-air valve continuously monitor airflow. If the differential pressure across either the supply- or exhaust-air valve in any room drops below 0.3 in. wg, the bubble-tight damper on

~I~

Airflow-tracking

control

1-----------, I I

· h--de H1\1.."... ncyparticulate-air filtration unit

I I

I I I

l___ ~

Venturi supply-air valve

to sesu

exhaust fans

Bubble-tight

damper

Supply air

Exhaust air ~

Transfer air from anteroom, 100 elm

Galvanized-steel _ ductwork Welded stainless- ~ steel ductwork

PaUent room

RGURE 6. Patient·room airflow.

the supply duct to that room closes immediately. The supply-airflow and exhaust-airflow set points are reset to emergency-mode minimum values.

When the main supply-duct static pressure and main exhaust-duct static pressure J"ise above 0.85 in. wg, the bubble-tight damper opens, sup-

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FEBRUARY 2011

HPAC ING..EERlNG

29

DESIGN OF A SPECIALIZED AIRBORNE-INFECTION-ISOLATION SUITE

ply- and exhaust-airflow set points are reset to their normal values, and the room reverts to normal opera­ tion. The room control sequences are illustrated in figures 4-6.

Particle Dynamics Clinically applicable distinctions are made between short-range airborne-infection routes (between individuals less than 3.28 ft apart) and long-range routes (within a room, between rooms, or between individuals greater than 3.28 ft apart). Small droplets may partici­ pate in short-range transmission, but are more likely than large drop­ lets to evaporate to become drop­ let nuclei. True long-range aerosol transmission becomes possible when droplets of infectious material are small enough to remain airborne almost indefinitely and be transmit­ ted over long distances. There is

Breathing zone around bed

RGURE 7. SCSU ventilation system.

essential agreement that particles with an aerodynamic diameter of 5 lJlTI or less are aerosols, while par­ ticles with an aerodynamic diameter of 20 llm are large droplets.

Methodology For the SCSU, computational fluid dynamics and particle tracking were

used to study the influence ofventiJa­ tion flow rate (12 ACH and 16 ACH), exhaust location (high exhaust, low exhaust, and the combination of high and low exhausts), and patient posi­ tion (sitting and lying) on the removal of aerosol generated by a cough. The model suite consisted of three rooms-main isolation room w ith

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DESIGN OF A SPECIALIZED AIRBORNE-INFECTION-ISOLATION SUITE

Rllllll: 3 . .. Balilrolfl

Room

V.ntllII

Alalll: I lila IIItInom Room

lInatNng

1

Sitting

12

Low

22"10

24"10

54"10

Brutlll•• 9%

42"10

6"10

Lying

12

Low

21"10

20/.

77%

7%

35% 29%

23%

2

4"10

67%

7%

3

Sitting

16

Low

27%

7%

66%

6"10

40%

7%

53%

5%

4

Lying

16

Low

26%

4%

71%

8"10

35%

6%

60%

7%

5

Sitting

12

I.Ai

15%

19%

66"10

12%

26%

200/.

55%

10%

6

Lying

12

I.Ai

13%

1%

85%

11 "10

24%

3"10

73%

11 %

7

Sitting

16

I.Ai

16%

18"10

66"10

13"10

30"10

200/.

50%

8%

8

Lying

16

I.Ai

15"10

1%

84%

8%

25%

4%

71%

14%

9

Sitting

12

High

13%

19"10

68%

14%

24%

21 %

55%

10%

10

Lying

12

Hi~

45%

3%

52%

6%

52%

5%

43%

7%

11

Sitting

16

High

24%

14%

62%

13"10

37%

17%

46%

8%

12

Lying

16

High

21%

1%

78%

9%

34%

64%

10%

20/.

TABLE 1. Case description and status of 3,000 particles 3 min and 5 min after a cough.

patient bed, bathroom, and ante­ room-connected via door gaps. A patient's cough was assumed to release 3,000 droplet nuclei with diameters of 3 llm. 2, 3 Further, the particles were assumed to be 93°F when released from the mouth.4

Results Three thousand particles were tracked individually for 5 min, with the number of particles removed from the room recorded every min­ ute. The location of each particle remaining in the room was recorded . Particular attention was pajd to the number of particles remaining in the breathing zone of the main room and the breathing zone around the bed where health-care workers were

most likely to be. The breatillng zone of the main room was defined as the space 3.6 ft to 5.75 ft from the floor; the breathing zone around the bed was defined as the space 9 in. from the edges of, and 3.6 ft to 5.75 ft above, the bed (Figure 7). Table 1 shows the percentage of particles removed from the suite 3 min and 5 min after a cough and the percentages of particles remaining in the bathroom, the main room, and the breathlng zone of the main room. During the first 3 min, the system removed 13 percent to 45 percent of the 3,000 particles. Withln 5 min, the percentage of particles removed increased to 25 to 55 percent, whlch is consistent with estimates 5 that, assuming a well-mixing condition,

_ 3mln 5 min 1,600 , . . . . - - - - . . . . , - - - - - - . , . - - - - - - ,

en

,....----...,..-----..,...."""'!"'.. ,. - --

1,600

1.400

I-------+-------+-------f

1,400 1 - - - - - - + - - - - - - +

1,200

1-- - ---.---.-+------+-------1

1,200

1,000

en

.90!

.~ ~

99 percent of particles will be removed after 9 min at 16 ACH. Note the percentage of particles in the bathroom is much higher when a sitting patient coughs than when a lying patient coughs. The reason is the rustribution of particles in the air current and the location of the bathroom. Figure 8 shows the number of particles removed 3 min and 5 min after the cough of a sitting patient and a lying patient. The combina ­ tion of low and high exhausts was least effective in removing particles. Generally, with the exception of Case 10, the most particles were removed with low exhaust and high flow, With a lying pat ient, 12 ACH (Case 10) removed more particles than 16 ACH

1------+------+

1,000 1 - - - - --1

.90!

~

800

~

600

800 600

400

400

200

200

o

o Case 1 Case 3 Low exhaust

Case 5 Case 7 Low and high exhaust

Case 9 Case 11 High exhaust

Sitting patient

Case 2 Case 4 Low exhaust

Case 6 Case 8 Case 10 Case 12 Low and high exhaust High exhaust

Lying patient

RGURE 8. Number of parUcles removed 3 min and 5 min after a cough. FEBRUARY 2011

HPAC ENGINEERING

31

DESIGN OF A SPECIALIZED AIRBORN E-INFECTlON-ISOLATION SUITE

(Case 12) with high exhaust. This can be explained by the flow pattern above the patient determined by the downward forced convection from the ceiling diffusers above the bed and the upward flow of the cough from the mouth of the lying patient. With greater downward flow (16 ACH, rather than 12 ACH) from the ceiling diffuser, the upward move­ ment of droplets carried by the cough of a lying patient couJd be suppressed and, thus, have difficulty reaching high exhausts. For a sitting patient, particles in the breathing zone generaUy were reduced from minutes 3 to 5 (Figure 9). For a lying patient, they sometimes

increased, depending on the ventila­ tion system and flow rate. Figure 10 shows the combination of low and high exhausts resulted in a higher number of particles in the breathing zone around the bed, especially in the cases (6 and 8) of a lying patient. High exhausts with a high flow rate (Case 12) did not remove particles around the bed effectively. Figure 10 indicates fewer particles around the bed with low exhausts. The nwnber of particles below the breathing zone was higher with low exhausts than with high exhausts (Figure 11). High exhausts with high flow rates (Case 12) did not seem to remove particles around the bed

450

450

400

400

350

..

Conclusions Conclusions that can be drawn from the study include: • Low exhaust outperforms other exhaust locations in terms of particle removal and number of particles remaining around a bed. • Increasing ventilation flow from 12 to 16 ACH generally helps to remove particles from an isolation

350

..

300

300

.JI

250

.JI

250

~

200

~

200

~

effectively. The number of particles above the breathing zone was higher with a lying patient regardless of flow rate and exhaust location (Fig­ ure 12). This was attributed primarily to the initial upward momentum of the cough jet.

~

150

150

100

100

50

50

0

0 Case 1 Case 3 Low exhaust

Case 5 Case 7 Low and high exhaust

Case 9 Case 11 High exhaust

Case 2 Case 4 Low exhaust

Sitting patient

Case 6 Case 8 Case 10 Case 12 Low and high exhaust High exhaust Lying patient

FIGURE 9. Number of particles remaining In breathing zone.

_

'"

3mln

5min

160

160

140

140

120

120

100

100

'"

.tI

.JI

~ ~

~

80

~

60

60

40

40

20

20

0

0 Case 1 Case 3 Low exhaust

Case 5

Case 7

Low and hiOh exhaust

Case 9

Case 11 HIgh exhaust

Sitting patient

FIGURE 10. Number of particles remaining In breathing zone around bed. 32

80

HPAC ENGINEERING

FEBRUARY 2011

Case 2 Case 4

Low exhaust

Case 6 Case 8 Case 10 Case 12 Low and high exhaust HiOh exhaust Lying patient

DESIGN OF A SPECIALIZED AIRBORNE·INFECTION·ISOLATION SUITE

1,000

900

800

800 700 .; ~ ~

700 600 •W 500 t ~ 400

....

600 500 400 300 200 100

o

Case 1 Case 3 Low exhaust

Case 5 Gase 7 Low and high exhaust

Case 9 case 11 High exhaust

300 200 100 0 Case 2 Gase4 Low exhaust

Sitting patient

case 6 Case 8 Case 10 Case 12 Low and high exhaust High exhaust Lying pallent

RGURE U. Number of particles below breaUllng zone•

• 3 min 5 min 2,000 - - - - - . . . . . . , . . . - - - - - - - - - - . . . . . , 1,800 1 - - - - - - - - - l - - - - - - + - - - - - - - 1 1,600 1 - - - - - - - + - - - - - - + - - - - - - - 1

1,400 1 - - - - - - + - - - - - - + - - - - - - - 1 ,; 1,2001-------+--------+--------1 ~ 1,000 1 - - - ­ ~ 8OOJ--­ 6001---­

Gase 1 Gase 3 Low exhaust

Case 5 Case 7 Low and high exhaust

Case 9 Gase 11 High exhaust

Case 2 Gase 4 Low exhaust

Sitting patient

Case 6 Case 8 Case 10 case 12 Low and high exhaust High exhaust Lying patient

RGURE 12. Number of particles above breathing zone.

room (except in cases of high exhaust and a lying patient coughing), but not necessarily a breathing zone. • The number of particles in a bathroom resulting from a cough in a main room is dependent on air-current particle distribution and bathroom location. Standard operating procedures are extremely important and shouJd be developed as part of the planning process, with consideration given to facility purpose and features .

References 1) Smith, P.W., et al. (2006) . De­ signing a biocontainment unit to care for patients with serious com­

municable diseases : A consensus statement. Biosecurity and Bioterror­ ism: Biodefense Strategy, Practice, and Science, 4, 351-365. Retrieved

from http://www.eunid.eu/public/ bioconteniment%20unit.pdf 2) Fennelly, K.P " Martyny, J.W., FuJton, K.E., Orme, I.M., Cave, D.M., & Heifets, L.B. (2004). Cough-gen­ erated aerosols of Mycobacterium tubercuJosis: A new method to study infectiousness . American Journal of Respiratory and Critical Care Medicine, 169, 604-609. 3) Fitzgerald, D., & Haas, D.W. Mycobacterium tuberculosis. In: Mandell, Douglas, and Bennett's principles and practice of infectious

diseases (6th ed .). (2005). Philadel ­ phia: Churchill Livingstone. 4) Hoppe, P. (1981) . Temperature of expired air under varying climatic conditions. International Journal of Biometeorology,25,127-132. 5) Centers for Disease Control and Prevention. (2005, December 30) . Guidelines for preventing the trans­ mission of mycobacterium tubercu­ losis in health-care settings, 2005 .

Morbidity and Mortality Weekly Report, 54, 20. Did you find this article useful? Send comments and suggestions to Executive Editor Scott Arnold at scott.arnold@

penton. com. FEBRUARY 2011

HPAC ENGINEERING

33