31
Class II Biological Safety Cabinets
The time required to carry out formalin decontamination is outlined below:
No.
Process
Time
1
Set-up & sealing the BSC to make it air tight
1 hour
2
Formalin vaporization
½ hour
3
Formalin contact time to obtain target log of 4-6 kill
8 – 10 hours
4
Ammonia vaporization to neutralize formalin
½ hour
5
Ammonia contact time to neutralize formalin
2 hours
6
Exhausting the ammonia residue
1 hour
7
Tear-down & cleaning the (substantial) residue
1 hour
TOTAL without ammonia neutralization
10½ – 12½ hours
TOTAL with ammonia neutralization
14 – 17 hours
Ammonia is used to neutralize formaldehyde. OSHA prescribes the ammonia STEL is 35 ppm for 15 minutes
exposure, 4 times a day, minimum of 60 minutes in between exposure.
Due to the adverse health effect of formalin gas, its use has been banned in some countries such as Germany,
Austria, and Switzerland. Other European countries are expected to follow suit. Two primary candidates to
replace formalin decontamination are chlorine dioxide gas and hydrogen peroxide vapor.
6.1.2.
Chlorine Dioxide Decontamination
Chlorine dioxide decontamination is performed by injecting chlorine gas (Cl
2
) into a cylinder filled with solid
sodium chlorite (NaClO
2
), which generates the greenish-yellow chloride dioxide gas (ClO
2
). Chlorine dioxide
decontamination is much faster than formalin. Being a true gas, it spreads quickly, without the need of pulsing
the BSC’s blower. It can rapidly kill the micro-organisms with high efficacy with just 1 hour contact time. User
must note that the concentration of chlorine gas inside the cabinet must decrease to a safe level (e.g. by using
scrubber system) before user should open the air tight seal. The Short-Term Permissible Exposure Limit (STEL)
for Chlorine Dioxide gas is 0.3 ppm. The time required for the entire process of chlorine dioxide
decontamination is as follows:
No.
Process
Time
1
Set-up & sealing the BSC to make it air tight
1 hour
2
Chlorine dioxide gassing
½ hour
3
Chlorine dioxide contact time
1 hour
4
Chlorine dioxide “scrubbing”
½ hour
5
Tear-down & cleaning the (minimal) residue
½ hour
TOTAL
3½ hours
Chlorine dioxide has the PEL of 0.1 ppm, compared to 0.75 ppm for formalin. In both processes airtight BSC
sealing is required to protect personnel from the gas exposure.
6.1.3.
Hydrogen Peroxide Decontamination
Hydrogen peroxide (H
2
O
2
) decontamination is performed by flash vaporization of an aqueous peroxide
mixture, creating a vapor that is distributed throughout the inside the BSC.
STERIS and BIOQUELL are two major vendors of hydrogen peroxide generators. There are significant
differences in operating principles.
•
The STERIS principle is to avoid condensation on surfaces to minimize corrosion and optimize vapor
distribution. The relative humidity inside the BSC must be lowered to 30% so that the remaining 70%
relative humidity can be occupied by the hydrogen peroxide vapor.
Summary of Contents for Class II
Page 26: ...16...
Page 64: ...54 8 2 AC2 _S_ Engineering Drawing...
Page 66: ...56 8 4 AC2 _D_ Engineering Drawing...
Page 67: ...57 Class II Biological Safety Cabinets...
Page 68: ...58 8 5 AC2 _G_ Engineering Drawing...
Page 70: ...60 8 7 AC2 2N7 Engineering Drawing A C 2 2 N 7 E n g i n e e r i n g D r a w i...
Page 71: ...61 Class II Biological Safety Cabinets...
Page 73: ......