Download Negative pressure in rooms

醫院負壓隔離病房之維護
衛生署 疾病管制局
中區傳染病防治醫療網
王任賢 指揮官
Negative Pressure rooms..
With current
methods, the
entire room is
potentially
contaminated by
infectious
droplets
Mechanical ventilation
•
Is created by using a fan to force air
exchange and to drive air flow
•
Works by generating negative pressure
in the room to drive airflow inward
To be effective, it is essential that:
•
•
•
All doors and windows kept closed
A minimum of 12 ACH is maintained
The ventilation system is well-designed,
maintained and operated
Principles of ventilation
Which is an easier way
to extinguish the
flame?
• Inhale (pull, exhaust)
• Exhale (push, supply)
Hospital Ventilation
Guidelines and Standards
CDC’s recommendations

Engineering Control

Local Exhaust Ventilation (i.e. source control)

General Ventilation

Air cleaning (HEPA filter, UVGI)
CDC’s recommendations

General Ventilation considerations

Dilution and removal of contaminants

Air-flow patterns within room

Air-flow direction in facilities

Negative pressure in rooms

TB isolation rooms
CDC’s recommendations for
Airborne Infection Isolation (AII)

Isolation of Patient infected with organisms
spread via airborne droplet nuclei <5 um in
diameter

≥ 6ACH for construction before 2001
≥
≥ 12 ACH for new construction
as of 2001


Negative pressure from corridor into the room

Air preferably exhausted to outside

Air may be recirculated, return air filtered through
HEPA
WHO Hospital Infection Control Guideline for
SARS and Recommendations in Descending
Order of Preference

Negative pressure rooms with the door closed

Single rooms with their own bathroom facilities

Cohort placement in an area with an independent
air supply, exhaust system and bathroom
facilities
Two ways to dilute and remove
contaminated air
First
choice:
Single
pass
Re-circulation + HEPA filtration
Rooms in a health facility
Designs to provide air mixing
exhaust
Airflow patterns are
affected by:
•
•
•
•
Air temperature
hcw
Location of furniture
Space configuration
supply
Movement of health
care workers (hcw)
exhaust
hcw
Short circuiting
•
Clean air is removed
before it is mixed
with room air
•
Contaminated air in
the room is not
effectively diluted or
removed
supply
exhaust
Nurse room
(Positive)
200 m3/h
225 m3/h
135 m3/h
135 m3/h
225 m3/h
200 m3/h
What is negative pressure?
Patient room
(Negative)
25 m3/h
Genesis of Negative Pressure
System
負壓系統的誕生
負壓抽氣扇
Negative Pressure Exhaust Fan
吸音板 – 減少噪音
Sound Absorption Board – Reduce Noise
防風防雨 – 防止空氣倒流
Fan Cowl – Reduce Back Pressure
輕便趟門加強負壓效果
Light Weight Folding Door
演進期
隱藏式天花抽氣扇
Recess type exhaust fan
HEPA過瀘器 0.3 微米 99.97%效率
HEPA Filter 0.3 Micron 99.97% efficiency
防回流氣閘
Non-return Damper
成熟期
DUCT
SupplySUPPLY
AirAIRDuct
送風喉
4-BED WARD MODULE
４人病房
Exhaust
AirDUCT
Duct
EXHAUST AIR
c/w AIR GRILLES
c/w air grilles
抽風喉
Negative pressure room
•
Air flows into room, from higher to lower
pressure
•
•
•
10% flow differential is minimum required
Keep doors and windows closed
Monitor to ensure negative pressure is
maintained
AII Rooms
AII Rooms
•
•
•
•
Maintain continuous negative pressure (2.5 Pa) in
relation to the air pressure in the corridor and ensure
monitoring
Ensure that rooms are well sealed
Provide ventilation to ensure > 12 ACH for new and
renovated rooms and > 6 ACH for existing rooms
Direct exhaust air to the outside, away from air intake
and populated areas. If this is not practical, air from
the room can be recirculated after passing through a
HEPA filter, ?UVGI
Guidelines
•
2001 AIA “Guidelines for Design and Construction of
Hospital and Health Care Facilities - ????NEW July 2006
•
2003 CDC “Guidelines for Environmental Infection
Control in Health-Care Facilities”
•
2004 JCAHO “Environment of Care – Essentials for
Health Care” Fourth Edition
The Americans
Institute of Architects
(AIA)
Joint Commission
on Accreditation of
Healthcare
Organizations
(JCAHO)
What about an anteroom?
AIA Guidelines Section: 7.2.C Airborne Infectious
Isolation Rooms does not require anterooms. The
requirement for an anteroom was dropped in the 199697 edition of the Guidelines on the basis of a study.
CDC Guideline: Does not require anteroom. For Viral
Hemorrhagic Fever and Smallpox, use AII preferably
with an anteroom – if not available use industrial-grade
HEPA filters to provide additional ACH
JCAHO EC Standard: No reference to anterooms
ASHRAE’s Design Manual
(American Society of Heating, Refrigeration, and Air-conditioning Engineers)
“HVAC Design Manual for Hospitals
and Clinics” 2003
Chapter 12: Room Design
On negative air pressure, as is required for
Airborne Infectious Isolation Rooms:
“…Through dilution, a 500 cubic feet anteroom (for
example) with an AVM of 50 cubic feet would
experience a 90 percent reduction in the transmission
of contaminated air to and from the isolation room. An
anteroom is recommended as a means of controlling
airborne contaminant concentration via containment
and dilution of the migrating air.”
Why add an anteroom or airlock?
•
•
•
To provide a barrier against loss of pressurization, and
against entry/exit of contaminated air into/out of
isolation room when the door to the airlock is opened
To provide a controlled environment in which
protective garments can be donned without
contamination before entry into and exit out of room
To provide a controlled environment in which
equipment and supplies can be transferred fro the
isolation room without contaminating the surrounding
area
Anterooms
Negative Pressure System
Verification
TB transmission in a TB dispensary,
Russia
Checking airflow in
the TB dispensary
Exhaust ventilation
Where does the air go?
Where does the air go?
Exhaust
Supply
Exhaust
Supply
Routine monitoring, recording

The operation of ventilation
systems should be regularly
monitored

Is the air moving? Is it
moving in the right direction?

Record performance and
dates of all routine
monitoring activities
Maintenance and inspection
of natural ventilation systems



Are the windows
open?
Designate a
person to routinely
inspect
Record results
Air Pressure Balancing

To prevent escape of droplet nuclei,
negative pressure

To maintain pressure relationship – clean
to dirty
Monitoring Negative Air Pressure
•
Pressure-measuring
devices
- Measure pressure at the
bottom of the door
- Audible warning with a
time delay
- Check continuous
monitoring devices at
least monthly using
smoke tubes
Airflow Pattern

Air flowing from corridor, through anteroom into isolation room

Temperature differential
Vaneometer (風速計)
Smoke Trail Test (STT)

Air flow – Vertical

Air flow - Horizontal
Negative pressure evaluation
•
•
•
•
Smoke tube
Pressure sensor
Flutter strips
Velocity meter
Smoke Test
•
•
Checked daily
•
If room air cleaners are
used they should be
running
•
Door must be closed
Hold 2 inches from
bottom of door
Smoke test to visualize air movement
Air Purification Systems



Air filtration system
Ultra-Violet light
Ozone
Air filtration System
Some common air contaminants Size (Microns)

Pollen :
5 – 100

Virus :
0.001 – 0.05

Aerosol :
0.005 – 50

Human Hair :
70 – 100

Bacteria :
0.35 – 10

Tobacco smoke :
0.01 – 0.5

Household dust :
0.05 – 100
Air filtration System - Air Filters


Pre-filters

Washable panel filter ＜ 50%

Disposable filter ＜ 50%
Final filters


High Efficiency Filter (Bag filter) = 85~95%
High Efficiency Particulate Air (HEPA)
filter = 0.3 micron & 99.97%
Ultra-Violet (UV) Light – nm- nanometer

Vaccum UV – UVV 90-200 nm

Short Wave UV – UVC 200-280 nm

Middle Wave UV – UVB 280-320 nm

Long Wave UV – UVA 320-400 nm

Greatest Germicidal Effectiveness – 250265 nm
Ultra-Violet – Factors Affecting
Killing Rate

Air Velocity – Higher velocity, more UVC
energy

Temperature – Within the system, too
cold, too hot, too humid, etc.

Relative Humidity (RH) – Higher RH,
more UVC energy

UV Light source location – Before or
after the object e.g. ducting, fan coil
units
Ultra-Violet - UV Lamp Efficiency
(Information source from RoboClean (HK) Co., Ltd.)
Ultra-Violet - Safety

Avoid exposure to UV rays e.g. eyes,
skin problem

Improve Ventilation when UVV is used (
generation of Ozone)

Avoid direct exposure of plastic
material
UV Radiation
•
Used to supplement other engineering
controls
•
Duct Irradiation
•
-
To recirculate air from an isolation room back into
the room.
-
Used in general use areas where air is recirculated
back into general ventilation
Upper Room Air Irradiation
-
Mounted on ceiling or wall
Ozone (O3) -臭氧之功能

殺菌

防腐

保鮮

解毒

醫療

增氧

美容

漂白
Ozone (O3) -臭氧的濃度國制上的標準

國際臭氧協會規定 0.05ppm(10小時/日)

美國國家標準規定(FDA) 0.05ppm (8小時/日)

德國國家標準規定0.10ppm

日本國家標準規定0.10ppm

法國國家標準規定0.12ppm
Measuring Equipment
a) Air Flow Measurement
 Anemometer
b) Temperature Measurement
 Thermometer
同心同德
工程人員
Engineering team
醫生
Doctors
感染控制組
Infection control
team
護士
Nurses
醫院行政
Hospital Administration
懇請賜教