Evaluation of Dry Fogging System for Microbial Inactivation
Carol Stansfield
Senior Biosafety Officer
Safety & Environmental Services
Canadian Science Centre for Human and Animal Health,
Winnipeg, Manitoba
Objectives
• Dry fog: An Overview
• Preliminary Studies
• Dry fog in a Containment Level 4 laboratory
• Dry fog vs computer
• Conclusions
Dry Fogging System
• Fog particle size: ~7.5
• 1/10 Minncare (Peracetic acid solution, MarCor,
USA)
– 22% Hydrogen peroxide, 4.5% Peracetic acid
Mechanism
• PAA is a strong oxidizer
• Oxidation of microbial cell proteins and enzyme
systems
• Not deactivated by peroxidase, catalases that
break down H2O2
Dry Fogging System
Advantages of PAA/Dry Fog System
• No residue/toxic byproducts (H2O, O2, CO2)
• Effective at low temperature (10°C)
• Portable (Dry Fog System)
• Rapid Decontamination
• Rapid Aeration
• High soil load tolerance
Dry Fogging System
Disadvantages of PAA
• Material compatibility
• Compatibility to electronics?
HCOH, GCD, DFS & VHP
HCOH GCD DFS VHP
Health Risk Carcinogen Non-carcinogen Non-carcinogen Non-carcinogen
Humidity Requirement 65 - 80% 65 - 80% 65 - 80% 10 - 60%
Microbicidal Activity Broad Broad Broad Broad
Neutralization Yes No, scrubbed or vented out No, aerated out No, catalytically destroyed
Real time con. Monitoring None Yes None Yes
By-products Hexamine (powder) Chlorites and chlorates H2O, O2, CO2 H2O, O2
EPA registration No Yes Yes Yes
Compatible to electronics No ? ? Yes
Aeration time Long Shortest Short Long
Cost $ $$$ $$ $$$$
Dry Fogging System (Portable)
Ikeuchi, USA • AKIMist “D” • 1-4 Nozzles • 2.5 - 12 L/hr • $5000 USD • 19L reservoir
Dry Fogging System (Mini)
MarCor, USA • MiniDry Fog System • 1 Nozzle • 500 mL/hr • $5000 USD • 500 mL reservoir
DFS Decontamination Process
3 Step Process
1. Dry Fogging
• Up to 75-80% RH.
2. Decontamination
• Overnight (~18 hours) for laboratory decons.
3. Aeration
• Down to <1ppm Hydrogen Peroxide.
DFS: Decontamination Cycle
0
20
40
60
80
9:41 AM 10:31 AM 11:21 AM 12:11 PM 1:01 PM 1:51 PM
RH % Temp °C
DFS: Process Validation
• Chemical Indicators (CI)
Changes from white to grey or black
Indicates a concentration greater than 1%
• Biological Indicators (BI) Spores of Geobacillus stearothermophilus (≥106)
Detection
• Dräger Polytron 2 w/H2O2
Sensor
• Dräger Pac III w/H2O2 Sensor
• Dräger H2O2 Detection Tubes
• Safe concentration: <1ppm
Small Scale Experiments: Setup
Small Scale Experiments: Setup
Disinfectant Testing: QCT
• Quantitative Carrier Test
Soil load (BSA, Mucin,
Tryptone)
Brushed stainless steel
Dried test inoculum
DFS: Effect of Soil Load
NG 30 min 6.0 Geobacillus stearothermophilus spores*
NG Overnight 5.8 Bacillus atrophaeus spores
NG 1 hour 6.2 Staphylococcus aureus
NG 1 hour 6.9 Escherichia coli
NG 2 hours 5.9 Vesicular stomatitis virus
Result Exposure Initial titre** Microbial agents
* Biological Indicator spore strips, contain no protein soil load
** titres are in LOG10
NG: No Growth
Dry Fogging Experiments: Setup
• Simulated lab space
• Metal framing,
polypropylene sheets
• ~700 ft3
Dry Fogging Experiments: Setup
CFIA CL4 Lab Decon using DFS
BI Locations
DFS: Main Lab vs. Autoclave Room
0
10
20
30
40
50
60
70
80
90
100
10
:00
12
:06
14
:12
16
:18
18
:24
20
:30
22
:36
0:4
2
2:4
8
4:5
4
7:0
0
9:0
6
11
:12
13
:18
15
:24
17
:30
19
:36
21
:42
23
:48
1:5
4
4:0
0
6:0
6
0
10
20
30
40
50
60
70
80
90
100
AUTOCLAVE ROOM TEMPERATURE
AUTOCLAVE ROOM RELATIVE-HUMIDITY
MAIN LAB RELATIVE-HUMIDITY
MAIN LAB TEMPERATURE
DFS: RH & Temp
0
10
20
30
40
50
60
70
80
90
1001
0:0
0
10
:35
11
:10
11
:45
12
:20
12
:55
13
:30
14
:05
14
:40
15
:15
15
:50
16
:25
17
:00
17
:35
18
:10
18
:45
19
:20
19
:55
20
:30
21
:05
21
:40
Re
lati
ve H
um
idit
y (%
RH
)
0
10
20
30
40
50
60
70
80
90
100
Tem
pera
ture
(°C
)
Relative Humidity
Temperature
Results: Failed BIs
What happened?
• The fog failed to rise to ceiling
• Raise fogger arm higher, articulating head fogger
• Heat from lab equipment caused stratification of T
• Higher temp will ↓H, prevent dry fog from contactng surface
• Add fans to circulate air, ↓heat load
• May not have achieved desired RH at ceiling
• Add fans to circulate air
Is Dry Fogging System Compatible to Electronics?
• Test Vehicle: Dell Inspiron 560
Sheet metal Plastic Aluminum Copper
Decon Chamber
Validation Conditions (RH)
0
10
20
30
40
50
60
70
80
90
10010:2
9
11:5
0
13:1
1
14:3
2
15:5
3
17:1
4
18:3
5
19:5
6
21:1
7
22:3
8
23:5
9
1:2
0
2:4
1
4:0
2
5:2
3
6:4
4
8:0
5
9:2
6
(HU
MID
ITY
%)
Validation Plan
PCs (5)
Control
PC (1)
Test Pcs
(4)
Powered on (2)
Powered off (2)
1 1
1 1
No more exposure,
only testing (1)
No more exposure,
only testing (1)
Results • BIs
PC, power on---> BI pass (3/3)
PC, power off---> BI pass (2/3)
• Physical
No visual evidence of corrosion, discoloration
• Functional
No evidence of functional impairment by PC-Doctor
Conclusions:
• Potential use for Dry fog/PAA in decontamination
of high containment laboratories and sensitive
electronics
• PAA able to penetrate soil load
• More validation studies required
Acknowledgements
• Jay Krishnan, Senior Biosafety Officer NML
• Laura Landry, Biosafety Officer NML
• Greg Fey, Containment Services PHAC
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