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